• #### Testing the equation of state for viscous dark energy

Some cosmological scenarios with bulk viscosity for the dark energy fluid are considered. Based on some considerations related to hydrodynamics, two different equations of state for dark energy are assumed, leading to power-law and logarithmic effective corrections to the pressure. The models are tested with the latest astronomical data from Type Ia supernovae (Pantheon sample), measurements of the Hubble parameter $H(z)$, Baryon Acoustic Oscillations and Cosmic Microwave Background radiation. In comparison with $\Lambda$CDM model, some different results are obtained and their viability is discussed. The power-law model shows some modest results, achieved under negative values of bulk viscosity, while the logarithmic scenario provide good fits in comparison to $\Lambda$CDM model.
Dark energyLambda-CDM modelBaryon acoustic oscillationsCosmic microwave backgroundSupernova Type IaVolume viscosityViscosityHubble parameterConfidence regionCosmological parameters...
• #### Galactic ionising photon budget during the Epoch ofReionisation in the Cosmic Dawn II simulation

Cosmic Dawn ("CoDa") II yields the first statistically-meaningful determination of the relative contribution to reionization by galaxies of different halo mass, from a fully-coupled radiation-hydrodynamics simulation of the epoch of reionization large enough ($\sim 100$ Mpc) to model global reionization while resolving the formation of all galactic halos above $\sim 10^8 \msol$. Cell transmission inside high-mass haloes is bi-modal -- ionized cells are transparent, while neutral cells absorb the photons their stars produce - and the halo escape fraction $\fesc$ reflects the balance of star formation rate ("SFR") between these modes. The latter is increasingly prevalent at higher halo mass, driving down $\fesc$ (we provide analytical fits to our results), whereas halo escape luminosity, proportional to $\fesc \times {\rm SFR}$, increases with mass. Haloes with dark matter masses within $6\cdot 10^{8} \msol < \mh < 3\cdot 10^{10} \msol$ produce $\sim 80$% of the escaping photons at z=7, when the Universe is 50% ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10% of the photon budget then, despite their high $\fesc$. High mass haloes are too few and too opaque, contributing $<10$% despite their high SFRs. The dominant mass range is lower (higher) at higher (lower) redshift, as mass function and reionization advance together (e.g. at z$=8.5$, x$_{\rm HI}=0.9$, $\mh < 5.10^9 \msol$ haloes contributed $\sim 80$%). Galaxies with UV magnitudes $M_{AB1600}$ between $-12$ and $-19$ dominated reionization between z$=6$ and 8.
ReionizationStar formation rateGalaxyVirial massIonizing radiationLuminosityStar formationEpoch of reionizationHigh massStar...
• #### Cosmological constraints from galaxy-lensing cross correlations using BOSS galaxies with SDSS and CMB lensingver. 2

We present cosmological parameter constraints based on a joint modeling of galaxy-lensing cross correlations and galaxy clustering measurements in the SDSS, marginalizing over small-scale modeling uncertainties using mock galaxy catalogs, without explicit modeling of galaxy bias. We show that our modeling method is robust to the impact of different choices for how galaxies occupy dark matter halos and to the impact of baryonic physics (at the $\sim2\%$ level in cosmological parameters) and test for the impact of covariance on the likelihood analysis and of the survey window function on the theory computations. Applying our results to the measurements using galaxy samples from BOSS and lensing measurements using shear from SDSS galaxies and CMB lensing from Planck, with conservative scale cuts, we obtain $S_8\equiv\left(\frac{\sigma_8}{0.8228}\right)^{0.8}\left(\frac{\Omega_m}{0.307}\right)^{0.6}=0.85\pm0.05$ (stat.) using LOWZ $\times$ SDSS galaxy lensing, and $S_8=0.91\pm0.1$ (stat.) using combination of LOWZ and CMASS $\times$ Planck CMB lensing. We estimate the systematic uncertainty in the galaxy-galaxy lensing measurements to be $\sim6\%$ (dominated by photometric redshift uncertainties) and in the galaxy-CMB lensing measurements to be $\sim3\%$, from small scale modeling uncertainties including baryonic physics.
GalaxyMilky WayCross-correlationCovarianceCosmological parametersPlanck missionCMB lensingSloan Digital Sky SurveyBaryon Oscillation Spectroscopic SurveyMock catalog...
• #### Fundamental Plane of BOSS galaxies: Correlations with galaxy properties, density field and impact on RSD measurements

Fundamental plane of elliptical galaxies can be used to predict the intrinsic size of galaxies and has a number of plausible application to study cosmology and galaxy physics. We present a detailed analysis of the fundamental plane of the SDSS-III BOSS LOWZ and CMASS galaxies. For the standard fundamental plane, we find a strong redshift evolution for the mean residual and show that it is primarily driven by the redshift evolution of the surface brightness of the galaxies. After correcting for the redshift evolution, the FP residuals are strongly correlated with the galaxy properties and some observational systematics. We show that the variations in the FP between the central and satellite galaxies, that have been observed in the literature, can primarily be explained by the correlation of the FP with the galaxy luminosity. We also measure the cross correlations of the FP residuals with the galaxy density field. The amplitude of the cross correlations depends on the galaxy properties and environment with brighter and redder galaxies showing stronger correlation. In general, galaxies in denser environments (higher galaxy bias ) show stronger correlations. We also compare FP amplitude with the amplitudes of intrinsic alignments of galaxy shapes (IA), finding the two to be correlated. Finally, using the FP residuals we also study the impact of intrinsic alignments on the constraint of growth rate using redshift space distortions. We do not observe any significant trends in measurements of the growth rate $f$ as function of the amplitude of FP-density correlations, resulting in null detection of the effects of IA on the RSD measurements.
GalaxyMilky WayCross-correlationRedshift-space distortionLuminosityIntrinsic alignmentSurface brightnessBaryon Oscillation Spectroscopic SurveyVelocity dispersionTwo-point correlation function...
• #### Reionization with galaxies and active galactic nuclei

In this work we investigate the properties of the sources that reionized the intergalactic medium (IGM) in the high-redshift Universe. Using a semi-analytical model aimed at reproducing galaxies and black holes in the first 1.5 Gyr of the Universe, we revisit the relative role of star formation and black hole accretion in producing ionizing photons that can escape into the IGM. Both star formation and black hole accretion are regulated by supernova feedback, resulting in black hole accretion being stunted in low-mass halos. We explore a wide range of combinations for the escape fraction of ionizing photons (redshift-dependent, constant and scaling positively with stellar mass) from both star formation ($\langle f_{\rm esc}^{\rm sf} \rangle$) and AGN ($f_{\rm esc}^{\rm bh}$) to find: (i) the ionizing budget is dominated by stellar radiation from low stellar mass ($M_*<10^9 {\rm M_\odot}$ ) galaxies at $z>6$ with the AGN contribution (driven by $M_{bh}>10^6 {\rm M_\odot}$ black holes in $M_* > 10^9 {\rm M_\odot}$ galaxies) dominating at lower redshifts; (ii) AGN only contribute $10-25\%$ to the cumulative ionizing emissivity by $z=4$ for the models that match the observed reionization constraints; (iii) if the stellar mass dependence of $\langle f_{\rm esc}^{\rm sf} \rangle$ is shallower than $f_{\rm esc}^{\rm bh}$, at $z<7$ a transition stellar mass exists above which AGN dominate the escaping ionizing photon production rate; (iv) the transition stellar mass decreases with decreasing redshift. While AGN dominate the escaping emissivity above the knee of the stellar mass function at $z \sim 6.8$, they take-over at stellar masses that are a tenth of the knee mass by $z=4$.
Active Galactic NucleiGalaxyReionizationStar formationStellar massIonizing radiationBlack holeAccreting black holeStarLuminosity...
• #### The Expansion of the Universe is Faster than Expected

The present rate of the expansion of our Universe, the Hubble constant, can be predicted from the cosmological model using measurements of the early Universe, or more directly measured from the late Universe. But as these measurements improved, a surprising disagreement between the two appeared. In 2019, a number of independent measurements of the late Universe using different methods and data provided consistent results making the discrepancy with the early Universe predictions increasingly hard to ignore. We review key advances realized by 2019: -- The local or late Universe measurement of the Hubble constant improved from 10% uncertainty twenty years ago to under 2% by the end of 2019. -- In 2019, multiple independent teams presented measurements with different methods and different calibrations to produce consistent results. -- These late Universe estimations disagree at 4$\sigma$ to 6$\sigma$ with predictions made from the Cosmic Microwave Background in conjunction with the standard cosmological model, a disagreement that is hard to explain or ignore.
Expansion of the UniverseThe early UniverseStandard cosmological modelCalibrationConjunctionHubble constant measurementCosmological modelCosmic microwave backgroundHubble constantUniverse...
• #### Early-type galaxy density profiles from IllustrisTNG: I. Galaxy correlations and the impact of baryonsver. 2

We explore the isothermal total density profiles of early-type galaxies (ETGs) in the IllustrisTNG simulation. For the selected 559 ETGs at $z = 0$ with stellar mass $10^{10.7}\mathrm{M}_{\odot} \leqslant M_{\ast} \leqslant 10^{11.9}\mathrm{M}_{\odot}$, the total power-law slope has a mean of $\langle\gamma^{\prime}\rangle = 2.011 \pm 0.007$ and a scatter of $\sigma_{\gamma^{\prime}} = 0.171$ over the radial range 0.4 to 4 times the stellar half mass radius. Several correlations between $\gamma^{\prime}$ and galactic properties including stellar mass, effective radius, stellar surface density, central velocity dispersion, central dark matter fraction and in-situ-formed stellar mass ratio are compared to observations and other simulations, revealing that IllustrisTNG reproduces many correlation trends, and in particular, $\gamma^{\prime}$ is almost constant with redshift below $z = 2$. Through analyzing IllustrisTNG model variations we show that black hole kinetic winds are crucial to lowering $\gamma^{\prime}$ and matching observed galaxy correlations. The effects of stellar winds on $\gamma^{\prime}$ are subdominant compared to AGN feedback, and differ due to the presence of AGN feedback from previous works. The density profiles of the ETG dark matter halos are well-described by steeper-than-NFW profiles, and they are steeper in the full physics (FP) run than their counterparts in the dark matter only (DMO) run. Their inner density slopes anti-correlates (remain constant) with the halo mass in the FP (DMO) run, and anti-correlates with the halo concentration parameter $c_{200}$ in both types of runs. The dark matter halos of low-mass ETGs are contracted whereas high-mass ETGs are expanded, suggesting that variations in the total density profile occur through the different halo responses to baryons.
Early-type galaxyIllustrisTNG simulationGalaxyAGN feedbackStellar massDark matterInner slopeDark matter fractionStrong gravitational lensingDark matter halo...
• #### Testing Galaxy Formation Simulations with Damped Lyman-${\alpha}$ Abundance and Metallicity Evolutionver. 2

We examine the properties of damped Lyman-$\alpha$ absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: {\sc Simba} and {\sc Technicolor Dawn}. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multi-frequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Ly-$\alpha$ forest mean transmission at $z>5$. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at $z\geq 3$, and both reproduce the observed neutral hydrogen cosmological mass density, $\Omega_{\rm HI}(z)$. However, the DLA abundance and metallicity distribution are sensitive to the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB and/or slow outflows under-produces the observed DLA abundance, but yields broad agreement with the observed DLA metallicity distribution. By contrast, faster outflows eject metals to larger distances, yielding more metal-rich DLAs whose observational selection may be more sensitive to dust bias. The DLA metallicity distribution in models adopting an ${\rm H}_2$-regulated star formation recipe includes a tail extending to $[M/H] \ll -3$, lower than any DLA observed to date, owing to curtailed star formation in low-metallicity galaxies. Our results show that DLA observations play an imporant role in constraining key physical ingredients in galaxy formation models, complementing traditional ensemble statistics such as the stellar mass and star formation rate functions.
MetallicityUltraviolet backgroundStar formationGalaxyStellar massGalaxy FormationStar formation rateStarMean transmitted fluxSupernova...
• #### Cosmic Reionization On Computers: The Galaxy-Halo Connection between $5 \leq z \leq10$

We explore the connection between the stellar component of galaxies and their host halos during the epoch of reionization ($5 \leq z\leq10$) using the CROC (Cosmic Reionization on Computers) simulations. We compare simulated galaxies with observations and find that CROC underpredicts the abundance of luminous galaxies when compared to observed UV luminosity functions, and analogously the most massive galaxies when compared to observed stellar mass functions. We can trace the deficit of star formation to high redshifts, where the slope of the star formation rate to stellar mass relation is consistent with observations, but the normalization is systematically low. This results in a star formation rate density and stellar mass density that is systematically offset from observations. However, the less luminous or lower stellar mass objects have luminosities and stellar masses that agree fairly well with observational data. We explore the stellar-to-halo mass ratio, a key quantity that is difficult to measure at high redshifts and that models do not consistently predict. In CROC, the stellar-to-halo mass ratio {\it decreases} with redshift, a trend opposite to some abundance matching studies. These discrepancies uncover where future effort should be focused in order to improve the fidelity of modeling cosmic reionization. We also compare the CROC galaxy bias with observational measurements using Lyman-Break Galaxy (LBG) samples. The good agreement of simulation and data shows that the clustering of dark matter halos is properly captured in CROC.
Cosmic Reionization On ComputersGalaxyStellar massMilky WayUV luminosity functionStellar mass functionLuminosityStar formation rateStar formationGalaxy bias...
• #### The properties of the interstellar medium of galaxies across time as traced by the neutral atomic carbon [CI]

We report ALMA observations of the neutral atomic carbon transitions [CI] and multiple CO lines in a sample of $\sim30$ main sequence galaxies at $z\sim1$, including novel information on [CI](2-1) and CO(7-6) for 7 of such normal objects. We complement our observations with a collection of $>200$ galaxies with coverage of similar transitions, spanning the $z=0-4$ redshift interval and a variety of ambient conditions from local to high-redshift starbursts. We find systematic variations in the [CI]/IR and [CI]/high-$J$ ($J=7$) CO luminosity ratios among the various samples. We interpret these differences as increased dense molecular gas fractions and star formation efficiencies in the strongest high-redshift starbursts with respect to normal main sequence galaxies. We further report constant $L'_{\rm [CI]2-1}$/$L'_{\rm [CI]1-0}$ ratios across the galaxy populations and redshifts, suggesting that gas temperatures $T_{\rm exc}$ traced by [CI] do not strongly vary. We find only a mild correlation with $T_{\rm dust}$ and that, generally, $T_{\rm exc} \lesssim T_{\rm dust}$. We fit the line ratios with classical PDR models, retrieving consistently larger densities and intensities of the UV radiation fields in submm galaxies than in main sequence and local objects. However, these simple models fall short in representing the complexity of a multiphase interstellar medium and should be treated with caution. Finally, we compare our observations with the Santa Cruz semi-analytical model of galaxy evolution, recently extended to simulate submm emission. While we confirm the success in reproducing the CO lines, we find systematically larger [CI] luminosities at fixed IR luminosity than predicted theoretically. This highlights the necessity of improving our understanding of the mechanisms regulating the [CI] emission on galactic scales. We release our data compilation to the community.
GalaxyMain sequence starLuminosityInterstellar mediumAtacama Large Millimeter ArrayActive Galactic NucleiStar formation rateLuminous infrared galaxyMilky WayLine emission...
• #### One-loop matching in the SMEFT extended with a sterile neutrino

We study the phenomenology of the simplest renormalisable model that, at low energy, leads to the effective field theory of the Standard Model extended with right-handed neutrinos ($\nu$SMEFT). Our aim is twofold. First, to contextualise new collider signatures in models with sterile neutrinos so far studied only using the bottom-up approach. And second and more important, to provide a thorough example of one-loop matching in the diagrammatic approach, of which other matching techniques and automatic tools can benefit for cross-checks. As byproducts of this work, we provide for the first time: (i) a complete off-shell basis for the $\nu$SMEFT and explicit relations between operators linked by equations of motion; (ii) a complete basis for the low-energy effective field theory ($\nu$LEFT) and the tree-level matching onto the $\nu$SMEFT; (iii) partial one-loop anomalous dimensions in the $\nu$LEFT. This way, our work comprises a new step forward towards the systematisation of one-loop computations in effective field theories, especially if the SM neutrinos are Dirac.
Effective field theory of the Standard ModelEffective field theorySterile neutrinoInfrared limitNeutrinoWilson coefficientsHiggs bosonLarge Hadron ColliderAnomalous dimensionCollider...
• #### Concluding Remarks at the Multifrequency Behaviour of High Energy Cosmic Sources -- XIII Workshop -- II

I summarise the concluding remarks I gave at the Multifrequency Behaviour of High Energy Cosmic Sources - XIII Workshop. That was not a summary talk and was meant to be provocative. I first give what I think the main message of the workshop was, then provide some (biased) highlights, touch upon the upcoming new facilities and the issues of "quantity vs. quality" and productivity in astronomy, and finally conclude with a look to the future. Astronomers who did not attend the workshop might still find the first two topics appealing and the last two thought-provoking.
BlazarBlack holeActive Galactic NucleiNeutrinoGravitational waveLuminosityBroad-line regionIceCube Neutrino ObservatoryLaser Interferometer Gravitational-Wave ObservatoryMagnetar...
• #### Gravitational radiation by magnetic field: application to millisecond magnetarsver. 2

We investigate the direct contribution of the magnetic field to the gravitational wave generation. To do so, we study the post-Newtonian energy-momentum tensor of the magnetized fluid and the post- Newtonian expansion of the gravitational potential in the wave zone. We show that the magnetic field appears even in the first post-Newtonian order of the multipole moment tensor. Then, we derive an explicit relativistic correction containing the magnetic field contribution to the well-known quadrupole formula. As an application of this derivation, we explicitly prove that the magnetic field of millisecond magnetars can be a promising source of the gravitational waves. We show that this type of gravitational wave is strong enough to be detected by the next generation of detectors.
MagnetarGravitational waveGravitational radiationRelativistic correctionMultipole momentsPost-Newtonian expansionQuadrupoleMagnetic fieldTensorPotential...
• #### Holographic Space-time and Quantum Information

The formalism of Holographic Space-time (HST) is a translation of the principles of Lorentzian geometry into the language of quantum information. Intervals along time-like trajectories, and their associated causal diamonds, completely characterize a Lorentzian geometry. The Bekenstein-Hawking-Gibbons-'t Hooft-Jacobson-Fischler-Susskind-Bousso Covariant Entropy Principle, equates the logarithm of the dimension of the Hilbert space associated with a diamond to one quarter of the area of the diamond's holographic screen, measured in Planck units. The most convincing argument for this principle is Jacobson's derivation of Einstein's equations as the hydrodynamic expression of this entropy law. In that context, the null energy condition (NEC) is seen to be the analog of the local law of entropy increase. The quantum version of Einstein's relativity principle is a set of constraints on the mutual quantum information shared by causal diamonds along different time-like trajectories. The implementation of this constraint for trajectories in relative motion is the greatest unsolved problem in HST. The other key feature of HST is its claim that, for non-negative cosmological constant or causal diamonds much smaller than the asymptotic radius of curvature for negative c.c., the degrees of freedom localized in the bulk of a diamond are constrained states of variables defined on the holographic screen. This principle gives a simple explanation of otherwise puzzling features of BH entropy formulae, and resolves the firewall problem for black holes in Minkowski space. It motivates a covariant version of the CKN\cite{ckn} bound on the regime of validity of quantum field theory (QFT) and a detailed picture of the way in which QFT emerges as an approximation to the exact theory.
DiamondEntropyHamiltonianBlack holeProper timeAnti de Sitter spaceDegree of freedomQuantum informationQuantum field theoryManifold...
• #### Turbulence in a self-gravitating molecular cloud core

Externally driven interstellar turbulence plays an important role in shaping the density structure in molecular clouds. Here we study the dynamical role of internally driven turbulence in a self-gravitating molecular cloud core. Depending on the initial conditions and evolutionary stages, we find that a self-gravitating core in the presence of gravity-driven turbulence can undergo constant, decelerated, and accelerated infall, and thus has various radial velocity profiles. In the gravity-dominated central region, a higher level of turbulence results in a lower infall velocity, a higher density, and a lower mass accretion rate. As an important implication of this study, efficient reconnection diffusion of magnetic fields against the gravitational drag naturally occurs due to the gravity-driven turbulence, without invoking externally driven turbulence.
TurbulenceMolecular cloudInfall velocityDynamical frictionPressure supportDissipationRadial velocity profileMass accretion rateFreezingTurbulent motion...
• #### The orbital phase space of contracted dark matter halos

We study the orbital phase-space of dark matter (DM) halos in the AURIGA suite of cosmological hydrodynamics simulations of Milky Way analogues. We characterise halos by their spherical action distribution, a function of the specific angular momentum, and the radial action, of the DM particles. By comparing DM-only and hydrodynamical simulations of the same halos, we investigate the contraction of DM halos caused by the accumulation of baryons at the centre. We find a small systematic suppression of the radial action in the DM halos of the hydrodynamical simulations, suggesting that the commonly used adiabatic contraction approximation can result in an underestimate of the density by ~ 8%. We apply an iterative algorithm to contract the AURIGA DM halos given a baryon density profile and halo mass, recovering the true contracted DM profiles with an accuracy of ~15%, that reflects halo-to-halo variation. Using this algorithm, we infer the total mass profile of the Milky Way's contracted DM halo. We derive updated values for the key astrophysical inputs to DM direct detection experiments: the DM density and velocity distribution in the Solar neighbourhood.
Dark matter haloDark matterDark matter particleStandard Halo modelN-body simulationLaboratory dark matter searchNavarro-Frenk-White profileVelocity distribution functionMilky WayVelocity dispersion...
• #### Generation of Solenoidal Modes and Magnetic Fields in Turbulence Driven by Compressive Driving

We perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving to study generation of solenoidal velocity component and small-scale magnetic field. We mainly focus on the effects of mean magnetic field ($B_0$) and the sonic Mach number ($M_s$). We also consider two different driving schemes in terms of correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. The former has a longer correlation timescale of forcing vectors, which is comparable to large-eddy turnover time, than the latter. Our findings are as follows. First, when we fix the value of $B_0$, the level of solenoidal velocity component after saturation increases as $M_s$ increases. A similar trend is observed for generation of magnetic field when $B_0$ is small. Second, when we fix the value of $M_s$, HD and MHD simulations result in similar level of the solenoidal component when $B_0$ $\lesssim$ 0.2 (or Alfven Mach number of $\sim$ 5). However, the level increases when $B_0$ $\gtrsim$ 0.2. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of $B_0$ irrespective of $M_s$. Third, generation of solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Lastly, when initial conditions are same, the finite-correlated driving always produces more solenoidal velocity and small-scale magnetic field components than the delta-correlated driving. We additionally analyze the vorticity equation to understand why higher $M_s$ and $B_0$ yield larger quantity of the solenoidal velocity component.
TurbulenceVorticityMach numberMagnetohydrodynamic turbulenceMagnetohydrodynamicsMagnetic field strengthMagnetic energy densityMagnetic pressureIntra-cluster mediumVortex stretching...
• #### The Transverse-Traceless Spin-2 Gravitational Wave Cannot Be A Standalone Observable Because It Is Acausalver. 3

We show, through an explicit calculation of the relevant Green's functions, that the transverse-traceless (TT) portion of the gravitational perturbations of Minkowski spacetime and of spatially flat cosmologies with a constant equation-of-state $w$ receive contributions from their isolated matter source(s) outside the past null cone of the observer. This implies the TT gravitational wave (GW) cannot be a standalone observable -- despite widespread (apparent) claims in the gravitational wave literature to the contrary. About a Minkowski background, all 4 of the gauge-invariant variables -- the two scalars, one vector and tensor -- play crucial roles to ensure the spatial tidal forces encoded within the gauge-invariant linearized Riemann tensor are causal. These gravitational tidal forces do not depend solely on the TT graviton but rather on the causal portion of its acceleration. However, in the far zone radiative limit, the flat spacetime TT' graviton Green's function does reduce to the causal tt' ones, which are the ones commonly used to compute gravitational waveforms. Similar remarks apply to the spin-1 photon; for instance, the electric field does not depend solely on the photon, but is the causal part of its velocity. As is known within the quantum theory of photons and linearized gravitons, there are obstacles to the construction of simultaneously gauge-invariant and Lorentz-covariant descriptions of these massless spin-1 and spin-2 states. Our results transparently demonstrate that the quantum operators associated with the helicity-1 photon and helicity-2 linear graviton both violate micro-causality: namely, they do not commute outside the light cone in flat and cosmological spacetimes.
Green's functionGravitational waveGravitonLight conesWave equationCurvature tensorTidal forceCausalityCosmologyPast light cones...
• #### The quantum vacuum in electromagnetic fields: From the Heisenberg-Euler effective action to vacuum birefringence

The focus of these lectures is on the quantum vacuum subjected to classical electromagnetic fields. To this end we explicitly derive the renowned Heisenberg-Euler effective action in constant electromagnetic fields in a rather pedagogical and easy to conceive way. As an application, we use it to study vacuum birefringence constituting one of the most promising optical signatures of quantum vacuum nonlinearity.
Heisenberg-Euler Effective ActionBirefringenceQuantum electrodynamicsPositronEffective actionLoop integralQuantum field theoryDegree of freedomFeynman diagramsOne-loop effective action...
• #### Geometric Inflation and Dark Energy with Axion $F(R)$ Gravity

We present a model of $F(R)$ gravity in the presence of a string theory motivated misalignment axion like particle materialized in terms of a canonical scalar field minimally coupled with gravity, and we study the cosmological phenomenology of the model, emphasizing mainly on the late-time era. The main result of the paper is that inflation and the dark energy era may be realized in a geometric way by an $F(R)$ gravity, while the axion is the dark matter constituent of the Universe. The $F(R)$ gravity model consists of an $R^2$ term, which as we show dominates the evolution during the early time, thus producing a viable inflationary phenomenology, and a power law term $\sim R^{\delta}$ with $\delta\ll 1$ and positive, which eventually controls the late-time era. The axion field remains frozen during the inflationary era, which is an effect known for misalignment axions, but as the Universe expands, the axion starts to oscillate, and its energy density scales eventually as we show, as $\rho_a\sim a^{-3}$. After appropriately rewriting the gravitational equations in terms of the redshift $z$, we study in detail the late-time phenomenology of the model, and we compare the results with the $\Lambda$CDM model and the latest Planck 2018 data. As we show, the model for small redshifts $0<z<5$ is phenomenologically similar to the $\Lambda$CDM model, however at large redshifts and deeply in the matter domination era, the results are different from those of the $\Lambda$CDM model due to the dark energy oscillations. For the late-time study we investigate the behavior of several well-known statefinder quantities, like the deceleration parameter, the jerk and $Om(z)$, and we demonstrate that the statefinders which contain lower derivatives of the Hubble rate have similar behavior for both the $\Lambda$CDM and the axion $F(R)$ gravity model.
AxionDark energyInflationary epochLambda-CDM modelDark matterInflationScalar fieldMisalignment mechanismCold dark matterFriedmann equations...
• #### Temporally Varying Universal Gravitational "Constant" and Speed of Light in Energy Momentum Squared Gravity

Energy Momentum Squared Gravity (EMSG) is a cosmological model where the scale factor is non vanishing at all times and hence does not favor big bang cosmology. However, the profile of density in the radiation dominated universe shows that EMSG supports inflationary cosmology. Inflationary cosmological models are successful in providing convincing answers to major cosmological issues like horizon problem, flatness problem and small value of cosmological constant but hitherto no model of inflation has been observationally confirmed. Owing to this, Varying Speed of Light (VSL) were introduced which are a class of cosmological models which disfavor inflation and propose an alternative route to solve these cosmological issues by just allowing the speed of light (and Newtonian Gravitational constant) to vary. VSL theories were motivated to address the shortcomings of inflation but do not address the shortcomings related to the initial big bang singularity. In this spirit, we present here a novel cosmological model which is free from both the "initial big bang singularity" and "inflation" by incorporating a mutually varying speed of light $c(t)$ and Newtonian gravitational constant $G(t)$ in the framework of EMSG. We report that in EMSG, for a dust universe ($\omega=0$), cosmological models for a time varying $c(t)$ and $G(t)$ and constant $c$ and $G$ are indistinguishable, whereas for a radiation dominated universe ($\omega = 1/3$), a mutually varying $c(t)$ and $G(t)$ provides an exiting alternative to inflationary cosmology which is also free from initial big bang singularity. We further report that for an ansatz of scale factor representing a bouncing cosmological model, the VSL theory can be applied to a quadratic $T$ gravity model to get rid of "inflation" and "big bang singularity" and concurrently solve the above mentioned cosmological enigmas.
Cosmological modelSpeed of lightScale factorBig Bang singularityInflationHorizon problemFlatness problemCosmological constantInflationary cosmologyBig Bang...
• #### Quantum Cosmology of Fab Four John Theory with Conformable Fractional Derivative

We study a quantization via fractional derivative of a nonminimal derivative coupling cosmological theory, namely, the Fab Four John theory. Its Hamiltonian version presents the issue of fractional powers in the momenta. That problem is solved here by the application of the so-called conformable fractional derivative. This leads to a Wheeler-DeWitt equation of second order, showing that a Bohm-de Broglie interpretation can be constructed. That combination of fractional quantization and Bohmian interpretation provides us a new quantization method, in which the quantum potential is the criterion to say if a quantum solution is acceptable or not to be further studied. We show that a wide range of solutions for the scale factor is possible. Among all of those, a bouncing solution analogous to the perfect fluid cosmology seems to deserve special attention.
QuantizationScale factorCosmologyHamiltonianQuantum cosmologyScalar fieldPerfect fluidFractional calculusHorndeski gravityAttention...
• #### About the symmetry of general relativity

In this work we use generalized deformed gauge groups for investigation of symmetry of general relativity (GR). GR is formulated in generalized reference frames, which are represented by (anholonomic in general case) affine frame fields. The general principle of relativity is extended to the requirement of invariance of the theory with respect to transitions between generalized reference frames, that is, with respect to the group GL^g of local linear transformations of affine frame fields. GR is interpreted as the gauge theory of the gauge group of translations T^g_M, and therefore is invariant under the space-time diffeomorphisms. The groups GL^g and T^g_M are united into group S^g_M, which is their semidirect product and is the complete symmetry group of the general relativity in an affine frame (GRAF). The consequence of GL^g -invariance of GRAF is the Palatini equation, which in the absence of torsion goes into the metricity condition, and vice versa, that is, is fulfilled identically in the Riemannian space. The consequence of the T^g_M -invariance of GRAF is representation of the Einstein equation in the superpotential form, that is, in the form of dynamic Maxwell equations (or Young-Mills equations). Deformation of the group S^g_M leads to renormalisation of energy-momentum of the gravitation field. At the end we show that by limiting admissible reference frames (by GL^g -gauge fixing) from GRAF, in addition to Einstein gravity, one can obtain other local equivalent formulations of GR: general relativity in an orthonormal frame, dilaton gravity, unimodular gravity, etc.
General relativitySymmetry groupSemidirect productTorsion tensorDiffeomorphismSuperpotentialGauge fixingOrthonormal frameDilatonGauge theory...
• #### Connection independent formulation of general relativity

A connection-independent formulation of general relativity is presented, in which the dynamics does not depend on the choice of connection. The gravity action in this formulation includes one additional scalar term in addition to the Einstein-Hilbert action. No conditions on the connection are imposed. Nevertheless, this formulation yields the Einstein equations, without adding the Gibbons-Hawking-York term even when a manifold has a boundary. Furthermore, this formulation yields a unified description of general relativity, teleparallel gravity, and symmetric teleparallel gravity.
General relativityTeleparallel gravityTorsion tensorManifoldLevi-Civita connectionEinstein-Hilbert actionAffine connectionScalar curvatureEinstein field equationsCovariant derivative...
• #### Gravity Induced Quantum Interference on Gravitational Wave Background

Gravity-induced quantum interference is an experiment that exhibits how a gravitational effect appears in quantum mechanics. In this famous experiments gravity was added to the system just classically. In our study we do the related calculations on a gravitational wave background. We realize that the effect of gravitational wave would be detectable in this quantum mechanical effect.
Gravitational waveInterferenceGravitational wave backgroundGravitational effectsGeodesicWave packetQuantum mechanicsKinematicsGeneral relativityDs meson...
• #### High-resolution spectroscopy of the GD-1 stellar stream localizes the perturber near the orbital plane of Sagittarius

The $100^\circ$-long thin stellar stream in the Milky Way halo, GD-1, has an ensemble of features that may be due to dynamical interactions. Using high-resolution MMT/Hectochelle spectroscopy we show that a spur of GD-1-like stars outside of the main stream are kinematically and chemically consistent with the main stream. In the spur, as in the main stream, GD-1 has a low intrinsic radial velocity dispersion, $\sigma_{V_r}\lesssim1\,\rm km\,s^{-1}$, is metal-poor, $\rm [Fe/H]\approx-2.3$, with little $\rm [Fe/H]$ spread and some variation in $\rm [\alpha/Fe]$ abundances, which point to a common globular cluster progenitor. At a fixed location along the stream, the median radial velocity offset between the spur and the main stream is smaller than $0.5\,\rm km\,s^{-1}$, comparable to the measurement uncertainty. A flyby of a massive, compact object can change orbits of stars in a stellar stream and produce features like the spur observed in GD-1. In this scenario, the radial velocity of the GD-1 spur relative to the stream constrains the orbit of the perturber and its current on-sky position to $\approx5,000\,\rm deg^2$. The family of acceptable perturber orbits overlaps the stellar and dark-matter debris of the Sagittarius dwarf galaxy in present-day position and velocity. This suggests that GD-1 may have been perturbed by a globular cluster or an extremely compact dark-matter subhalo formerly associated with Sagittarius.
GD-1 stellar streamRadial velocitySagittarius Dwarf Elliptical GalaxyStarDark matter subhaloStellar streamGlobular clusterMilky WayDark matterVelocity dispersion...
• #### The cosmic recombination history in light of EDGES measurements of the cosmic dawn 21-cm signal

The recent EDGES measurements of the global 21-cm signal from the cosmic dawn suggest that the kinetic temperature of the inter-galactic medium (IGM) might be significantly lower compared to its expected value. The colder IGM directly affects the hydrogen recombination of the universe during the cosmic dawn and dark ages by enhancing the rate of recombinations. Here, we study and quantify, the impact of the colder IGM scenario on the recombination history of the universe in the context of DM-baryonic interaction model which is widely used to explain the EDGES 21-cm signal. We find that, in general, the hydrogen ionisation fraction gets suppressed during the dark ages and cosmic dawn and the suppression gradually increases at lower redshifts. However, accurate estimation of the ionisation fraction requires knowledge of the entire thermal history of the IGM, from the thermal decoupling of hydrogen gas and the CMBR to the cosmic dawn. It is possible that two separate scenarios which predict very similar HI differential temperature during the cosmic dawn and are consistent with the EDGES 21-cm signal might have very different IGM temperature during the dark ages. The evolutions of the ionization fraction in these two scenarios are quite different. This prohibits us to accurately calculate the ionisation fraction during the cosmic dawn using the EDGES 21-cm signal alone. We find that the changes in the ionisation fraction w.r.t the standard scenario at redshift $z \sim 17$ could be anything between $\sim 0 \%$ to $\sim 36 \%$. This uncertainty remains even for a more precise measurement of the 21-cm signal from the cosmic dawn. However, the IGM temperature measured at two widely separated epochs should be able to constrain the ionisation fraction more accurately.
Cosmic DawnIntergalactic mediumEDGES experimentHydrogen 21 cm lineIGM temperatureRecombinationCosmic microwave backgroundDark AgesDark matterBrightness temperature...
• #### EDGES signal in presence of magnetic fieldsver. 2

We study the 21-cm differential brightness temperature in the presence of primordial helical magnetic fields for redshift $z=10-30$. It is shown that the gas temperature can be lowered to 3.2 degree Kelvin at $z=17$ by the alpha-effect due to the twisting of magnetic field lines by eddies generated due to the turbulence generated at earlier times. Using the EDGES results, we find the upper and lower limits on the primordial magnetic field to be $6\times 10^{-3}~{\rm nG}$ & $5\times 10^{-4}~{\rm nG}$ respectively. We also discuss the effect of Ly$\alpha$ background on the bounds. Our results do not require any new physics in terms of dark-matter.
EDGES experimentAlpha-effectCoolingX-ray heatingCosmological magnetic fieldDark matterHydrogen 21 cm lineTurbulenceKelvinHelical magnetic field...
• #### Gravitational waves from neutrino mass and dark matter genesis

We introduce a model in which the genesis of dark matter and neutrino masses is associated with a first order phase transition of a scalar singlet field. During the phase transition a source right-handed neutrino acquires a spacetime-dependent mass dynamically, a small fraction of which is converted via resonant oscillations into a very weakly mixed dark right-handed neutrino with the observed dark matter relic abundance. Neutrino masses are generated via a traditional two right-handed neutrino type-I seesaw between a third right-handed neutrino and the source neutrino. The gravitational waves produced during the phase transition have a peak frequency that increases with the dark matter mass, and are detectable at future gravitational wave interferometers for dark matter masses in the 1 MeV - 20 GeV range. For source right-handed neutrinos heavier than a GeV, successful leptogenesis is also possible.
Sterile neutrinoDark matterPhase transitionsGravitational waveNeutrino massDark matter particle massLeptogenesisLandau-Zener transitionType I seesawInterferometers...
• #### Hunting for ALPs with Lepton Flavor Violationver. 2

We examine the low-energy signatures of axion-like particles (ALPs) in lepton flavor violating (LFV) processes. By using a dimension-5 effective Lagrangian, we compute the most general ALP contributions to LFV decays of leptons and mesons. The provided expressions are valid for any choice of ALP mass and couplings. We explore the complementarity of different processes, identifying specific patterns to be experimentally tested. Constraints on LFV couplings are derived from existing data and prospects for forthcoming experiments are also discussed. As a by-product, we revisit the possibility of a simultaneous explanation of the observed discrepancies in the muon and electron $g-2$ through ALP interactions.
Axion-like particleLepton flavour violationALP couplingForm factorAxion massBranching ratioALP interactionsPseudoscalarStandard ModelDecay mode...
• #### Dispersive and Absorptive CP Violation in $D^0- \overline{D^0}$ Mixing

In the precision era, CP violation in $D-\bar D$ mixing is ideally described in terms of the dispersive and absorptive phases $\phi_f^M$ and $\phi_f^\Gamma$, parametrizing CP violation (CPV) in the interference of $D^0$ decays with and without dispersive (absorptive) mixing. These are distinct and separately measurable effects. This formalism is applied to (i) Cabibbo favored/doubly Cabibbo suppressed (CF/DCS) decays $D^0 \to K^\pm X$; (ii) CF/DCS decays $D^0 \to K_{S,L} X$, including the impact of $\epsilon_K$, and (iii) singly Cabibbo suppressed (SCS) decays. Expressions for the time-dependent CP asymmetries simplify: Indirect CPV only depends on $\phi_f^M$ (dispersive CPV), whereas $\phi_f^\Gamma$ (absorptive CPV) can only be probed with non-CP eigenstate final states. Measurements of the final state dependent phases $\phi_f^M$, $\phi_f^\Gamma$ determine the phases $\phi_2^M$ and $\phi_2^\Gamma$, which are the arguments of the dispersive and absorptive mixing amplitudes $M_{12}$ and $\Gamma_{12}$, relative to their dominant ($\Delta U=2$) $U$-spin components. $\phi_2^M$ and $\phi_2^\Gamma$ are experimentally accessible due to approximate universality: in the SM, $\phi_f^M-\phi_2^M$ and $\phi_f^\Gamma-\phi_2^\Gamma$ are negligible in case (i) above; and below $10\%$ in (ii), up to precisely known $O(\epsilon_K )$ corrections. In case (iii), the pollution enters at $O(\epsilon)$ in $U$-spin breaking and can be significant, but is $O(\epsilon^2)$ in the average over $f=K^+K^-$, $\pi^+\pi^-$. U-spin based estimates yield $\phi_2^M, \phi_2^\Gamma = O(0.2\%)$ in the SM. The current fit to the data thus implies an $O(10)$ window for new physics at $2\sigma$. A fit based on naively extrapolated experimental precision at the LHCb Phase II upgrade suggests that sensitivity to $\phi_2^{M,\Gamma}$ in the SM may be achievable in the precision era.
CP violationStandard ModelCP asymmetryLHCb experimentDecay widthInterferenceCP-oddBELLE IIQuantum chromodynamicsDecay rate...
• #### The signature of primordial black holes in the dark matter halos of galaxies

The aim of this paper is to investigate the claim that stars in the lensing galaxy of a gravitationally lensed quasar system can always account for the observed microlensing of the individual quasar images. A small sample of gravitationally lensed quasar systems was chosen where the quasar images appear to lie on the fringe of the stellar distribution of the lensing galaxy. As with most quasar systems, all the individual quasar images were observed to be microlensed. The surface brightness of the lensing galaxy at the positions of the quasar images was measured from HST frames, and converted to stellar surface mass density. The surface density of smoothly distributed dark matter at the image positions was obtained from lensing models of the quasar systems and applied to the stellar surface mass density to give the optical depth to microlensing. This was then used to assess the probability that the stars in the lensing galaxy could be responsible for the observed microlensing. The results were supported by microlensing simulations of the star fields around the quasar images combined with values of convergence and shear from the lensing models. Taken together, the probability that all the observed microlensing is due to stars was found to be ~0.0003. Errors resulting from surface brightness measurement, mass-to-light ratio and the contribution of the dark matter halo do not significantly affect this result. It is argued that the most plausible candidates for the microlenses are primordial black holes, either in the dark matter halos of the lensing galaxies, or more generally distributed along the lines of sight to the quasars.
Gravitational microlensingQuasarGravitational lens galaxyStarDark matterLight curveStellar populationsPrimordial black holeGalaxyMass to light ratio...
• #### UV & U-band luminosity functions from CLAUDS and HSC-SSP -- I. Using four million galaxies to simultaneously constrain the very faint and bright regimes to $z \sim 3$ver. 2

We constrain the rest-frame FUV (1546\AA), NUV (2345\AA) and U-band (3690\AA) luminosity functions (LFs) and luminosity densities (LDs) with unprecedented precision from $z \sim 0.2$ up to $z \sim 3$ (FUV, NUV) and $z \sim 2$ (U band). Our sample of more than 4.3 million galaxies, selected from the CFHT Large Area $U$-band Deep Survey (CLAUDS) and HyperSuprime-Cam Subaru Strategic Program (HSC-SSP) data lets us probe the very faint regime (down to $M_\mathrm{FUV}$, $M_\mathrm{NUV}$, $M_\mathrm{U} \simeq -15$) while simultaneously detecting very rare galaxies at the bright end down to comoving densities $<10^{-5}$ Mpc$^{-3}$. Our FUV and NUV LFs are well fitted by a single Schechter function, with faint-end slopes that are very stable up to $z\sim 2$. We confirm, but self-consistently and with much better precision than previous findings that the LDs at all three wavelengths increase rapidly with lookback time to $z\sim1$, and then much more slowly at $1<z<2$-$3$. Evolution of the FUV and NUV LFs and LDs at $z<1$ is driven almost entirely by the fading of the characteristic magnitude, $M^\star_{UV}$, while at $z>1$ it is due to the evolution of both $M^\star_{UV}$ and the characteristic number density $\phi^\star_{UV}$. In contrast, the U-band LF has an excess of faint galaxies and is fitted with a double-Schechter form; $M^\star_\mathrm{U}$ and both $\phi^\star_\mathrm{U}$ components, as well as the bright-end slope evolve throughout $0.2<z<2$, while the faint-end slope appears to be constant over $0.05 < z < 0.6$ (where the double-Schechter profile of the U-band LF is undeniable), at least. We present tables of our Schechter parameters and LD measurements that can be used for testing theoretical galaxy evolution models and forecasting future observations.
Luminosity functionGalaxyAbsolute magnitudeHyper Suprime-CamLuminosityStarCompletenessSchechter functionRedshift binsPhotometric redshift...
• #### Dynamical self-friction: how mass loss slows you down

We investigate dynamical self-friction, the process by which material that is stripped from a subhalo torques its remaining bound remnant, which causes it to lose orbital angular momentum. By running idealized simulations of a subhalo orbiting within an analytical host halo potential, we isolate the effect of self-friction from traditional dynamical friction due to the host halo. While at some points in a subhalo's orbit the torque of the stripped material can boost the orbital angular momentum of the remnant, the net effect over the long term is orbital decay regardless of the initial orbital parameters or subhalo mass. In order to quantify the strength of self-friction, we run a suite of simulations spanning typical host-to-subhalo mass ratios and orbital parameters. We find that the time-scale for self-friction, defined as the exponential decay time of the subhalo's orbital angular momentum, scales with mass ratio and orbital circularity similar to standard dynamical friction. The decay time due to self-friction is roughly an order of magnitude longer, suggesting that self-friction only contributes at the 10 percent level. However, along more radial orbits, self-friction can occasionally dominate over dynamical friction close to pericentric passage, where mass stripping is intense. This is also the epoch at which the self-friction torque undergoes large and rapid changes in both magnitude and direction, indicating that self-friction is an important process to consider when modeling pericentric passages of subhaloes and their associated satellite galaxies.
Dark matter subhaloOrbital angular momentum of lightDynamical frictionMass ratioFriction torqueSatellite galaxyGalaxyElliptical orbitNumerical simulationVirial radius...
• #### The Density Matrix Renormalization Group in Chemistry and Molecular Physics: Recent Developments and New Challengesver. 2

In the past two decades, the density matrix renormalization group (DMRG) has emerged as an innovative new method in quantum chemistry relying on a theoretical framework very different from that of traditional electronic structure approaches. The development of the quantum chemical DMRG has been remarkably fast: it has already become one of the reference approaches for large-scale multiconfigurational calculations. This perspective discusses the major features of DMRG, highlighting its strengths and weaknesses also in comparison to other novel approaches. The method is presented following its historical development, starting from its original formulation up to its most recent applications. Possible routes to recover dynamical correlation are discussed in detail. Emerging new fields of applications of DMRG are explored, in particular its time-dependent formulation and the application to vibrational spectroscopy.
Density matrix renormalization groupMatrix product statesHamiltonianConfiguration interactionComputer algebra systemOptimizationDensity functional theoryExcited stateCoupled cluster methodPerturbation theory...
• #### Operator product expansion coefficients in the exact renormalization group formalism

We study how to compute the operator product expansion coefficients in the exact renormalization group formalism. After discussing possible strategies, we consider some examples explicitly, within the $\epsilon$-expansions, for the Wilson-Fisher fixed points of the real scalar theory in $d=4-\epsilon$ dimensions and the Lee-Yang model in $d=6-\epsilon$ dimensions. Finally we discuss how our formalism may be extended beyond perturbation theory.
OPE coefficientsOperator product expansionWilson-Fisher fixed pointMomentum spaceConformal field theoryTwo-point correlation functionRenormalization groupPerturbation theoryGaussian fixed pointOne particle irreducible...
• #### The topological magnon bands in the Flux state in Sashtry-Sutherland lattice

We investigate low energy magnon excitations above the non-collinear flux state and non-coplanar canted flux state in a Heisenberg anti-ferromagnet with Dzyaloshinskii-Moriya interaction~(DMI) on a Sashtry-Sutherland lattice.While previous studies have shown the presence of topological magnetic excitation in the dimer and ferromagnetic phases on the Shastry-Sutherland lattice, our results establish the non-trivial topology of magnons in the anti-ferromagnetic flux and canted flux states. Our results uncover the existence of a multitude of topological phase transitions in the magnon sector -- evidenced by the changing Chern numbers of the single magnon bands -- as the Hamiltonian parameters are varied, even when the ground state remains unchanged. The thermal Hall conductivity is calculated and its derivative is shown to exhibit a logarithmic divergence at the phase transitions, independent of the type of band touching involved. This may provide a useful means to identify the energy at which the transition occurs. Finally, we propose the way to realize the studied model in a practical material.
MagnonDzyaloshinskii-Moriya interactionBerry phaseHamiltonianChern numberTopological phase transitionPhase transitionsBrillouin zoneTopological orderDirac point...
• #### Effects of magnon-magnon interactions in a noncollinear magnet induced by combination of a symmetric and an antisymmetric exchange interaction

We study magnon-magnon interactions and their effects in a spiral magnet induced by combination of an antiferromagnetic Heisenberg interaction and a Dzyaloshinsky-Moriya interaction. We show that the main effect of magnon-magnon interactions on low-energy magnons is to renormalize the coefficient of energy dispersion. This could explain why some experiments are consistent with the noninteracting theory. We also show that although the magnon-magnon interactions induce the pair amplitude for low-energy magnons, its effect on the excitation energy is negligible. This suggests that for magnons the finite pair amplitude does not necessarily accompany the pair condensation.
MagnonHamiltonianSelf-energyCondensationLong wavelength limitAntiferromagneticBogoliubov transformationGreen's functionPerturbation theoryRenormalization...
• #### Spontaneous symmetry breaking of an interacting Chern insulator on a topological square lattice

The interplay between topology and correlation lies at the forefront of modern condensed matter physics. In this paper, we study the extended fermion-Hubbard model, including the on-site as well as the nearest-neighbor repulsive interactions, on a topological square lattice that supports the Chern insulator. Within the mean-field method, we find that the spontaneous symmetry breaking (SSB) charge-density wave or antiferromagnetic insulator dominates the system when the onsite or nearest-neighbor interactions are strong enough. It is interesting that the antiferromagnetic Chern insulator will appear in the phase diagram when there is an explicitly nonvanishing sublattice potential. In addition, we explore how a finite-size ribbon structure affects the phase diagram and point out that the critical interaction for SSB occurs with weaker strength than the bulk system.
AntiferromagneticSpontaneous symmetry breakingCharge density wavePhase diagramInsulatorsDirac pointMean fieldTime-reversal symmetryHubbard modelMagnetic order...
• #### Positive Populations

A positive structure on the varieties of critical points of master functions for KZ equations is introduced. It comes as a combination of the ideas from classical works by G.Lusztig and a previous work by E.Mukhin and the second named author.
Critical pointWronskianVector spaceIsomorphismMutationAutomorphismMorphismUnipotentKnizhnik-Zamolodchikov equationsSubgroup...
• #### On index expectation curvature for manifolds

Index expectation curvature K(x) = E[i_f(x)] on a compact Riemannian 2d-manifold M is the expectation of Poincare-Hopf indices i_f(x) and so satisfies the Gauss-Bonnet relation that the interval of K over M is Euler characteristic X(M). Unlike the Gauss-Bonnet-Chern integrand, such curvatures are in general non-local. We show that for small 2d-manifolds M with boundary embedded in a parallelizable 2d-manifold N of definite sectional curvature sign e, an index expectation K(x) with definite sign e^d exists. The function K(x) is constructed as a product of sectional index expectation curvature averages K_k(x) = E[i_k(x)] of a probability space of Morse functions f for which i_f(x) is the product of i_k(x), where the i_k are independent and so uncorrelated.
CurvatureManifoldEuler characteristicCritical pointSectional curvatureFrame bundleGeodesicProduct metricOrthonormal frameHopf conjecture...
• #### Hadoop Perfect File: A fast access container for small files with direct in disc metadata accessver. 2

Storing and processing massive small files is one of the major challenges for the Hadoop Distributed File System (HDFS). In order to provide fast data access, the NameNode (NN) in HDFS maintains the metadata of all files in its main-memory. Hadoop performs well with a small number of large files that require relatively little metadata in the NN s memory. But for a large number of small files, Hadoop has problems such as NN memory overload caused by the huge metadata size of these small files. We present a new type of archive file, Hadoop Perfect File (HPF), to solve HDFS s small files problem by merging small files into a large file on HDFS. Existing archive files offer limited functionality and have poor performance when accessing a file in the merged file due to the fact that during metadata lookup it is necessary to read and process the entire index file(s). In contrast, HPF file can directly access the metadata of a particular file from its index file without having to process it entirely. The HPF index system uses two hash functions: file s metadata are distributed through index files by using a dynamic hash function and, for each index file, we build an order preserving perfect hash function that preserves the position of each file s metadata in the index file. The HPF design will only read the part of the index file that contains the metadata of the searched file during its access. HPF file also supports the file appending functionality after its creation. Our experiments show that HPF can be more than 40% faster file s access from the original HDFS. If we don t consider the caching effect, HPF s file access is around 179% faster than MapFile and 11294% faster than HAR file. If we consider caching effect, HPF is around 35% faster than MapFile and 105% faster than HAR file.
File systemCachingArchitectureFacebookOptimizationBig dataFragmentationSatellite ImageGoogle.comCollaborative filtering...
• #### Global Constraints on a Heavy Neutrinover. 3

We estimate constraints on the existence of a heavy, mostly sterile neutrino with mass between 10 eV and 1 TeV. We improve upon previous analyses by performing a global combination and expanding the experimental inputs to simultaneously include tests for lepton universality, lepton-flavor-violating processes, electroweak precision data, dipole moments, and neutrinoless double beta decay. Assuming the heavy neutrino and its decay products are invisible to detection, we further include, in a self-consistent manner, constraints from direct kinematic searches, the kinematics of muon decay, cosmology, and neutrino oscillations, in order to estimate constraints on the values of $|U_{e4}|^2$, $|U_{\mu4}|^2$, and $|U_{\tau4}|^2$.
Sterile neutrinoStandard ModelKinematicsNeutrinoLepton universality of gauge couplingsMuon decayNeutrino oscillationsNeutrinoless double-beta decayDecay rateCharged lepton...
• #### Impact of sterile neutrinos on nuclear-assisted cLFV processesver. 2

We discuss charged lepton flavour violating processes occurring in the presence of muonic atoms, such as muon-electron conversion in nuclei $\text{CR}(\mu -e, \text{ N})$, the (Coulomb enhanced) decay of muonic atoms into a pair of electrons BR($\mu^- e^- \to e^- e^-$, N), as well as Muonium conversion and decay, $\text{Mu}-\bar{\text{Mu}}$ and $\text{Mu}\to e^+ e^-$. Any experimental signal of these observables calls for scenarios of physics beyond the Standard Model. In this work, we consider minimal extensions of the Standard Model via the addition of sterile fermions, providing the corresponding complete analytical expressions for all the considered observables. We first consider an "ad hoc" extension with a single sterile fermion state, and investigate its impact on the above observables. Two well motivated mechanisms of neutrino mass generation are then considered: the Inverse Seesaw embedded into the Standard Model, and the $\nu$MSM. Our study reveals that, depending on their mass range and on the active-sterile mixing angles, sterile neutrinos can give significant contributions to the above mentioned observables, some of them even lying within present and future sensitivity of dedicated cLFV experiments. We complete the analysis by confronting our results to other (direct and indirect) searches for sterile fermions.
Standard ModelSterile neutrinoMuoniumNeutrinoMuonLepton flavour violationForm factorNeutrino massExtensions of the standard modelFlavour...
• #### On Constructive-Deductive Method For Plane Euclidean Geometry

Constructive-deductive method for plane Euclidean geometry is proposed and formalized within Coq Proof Assistant. This method includes both postulates that describe elementary constructions by idealized geometric tools (pencil, straightedge and compass), and axioms that describes properties of basic geometric figures (points, lines, circles and triangles). The proposed system of postulates and axioms can be considered as a constructive version of the Hilbert's formalization of plane Euclidean geometry.
Euclid missionOrientationSuperpositionGraphiteUndefinedInteractive theorem proverDualityInferenceGlassFinite size...
• #### Thermal spin transport and spin in thermoelectrics

This article reviews the principles that govern the combined transport of spin, heat, and charge. The extensive thermodynamic quantity associated with spin transport is the magnetization; its Onsager-conjugate force is in general the derivative of the free energy with respect to the magnetization. Spins are carried in one of two ways: (1) by spin-polarized free electrons in magnetic metals and doped semiconductors, or (2) by spin waves (magnons) that reside on localized electrons on unfilled d- or f-shells of transition metal or rare-earth elements. The paper covers both cases in separate chapters. In both cases, it is possible to define a spin chemical potential whose gradient is the more practical conjugate force to spin transport. The paper further describes the anomalous Hall, spin Hall, and inverse spin Hall effects in magnetic and non-magnetic solids with strong spin-orbit coupling because these effects are used to generate and measure spin fluxes. Spin transport across interfaces is described next, and includes spin pumping and spin transfer torque. The final chapter then puts all these concepts together to describe the spin-Seebeck, spin-Peltier, and magnon-drag effects, which exist in ferromagnetic, antiferromagnetic, and even paramagnetic solids. Magnon-drag, in particular, is a high-temperature effect that boosts the thermopower of metals by an order of magnitude and that of semiconductors by a factor of 2 or 3 above the electronic diffusion thermopower. This is the only example where a spin-driven effect is larger than a charge-driven effect. Magnon drag leads a simple binary paramagnetic semiconductor, MnTe, to have zT > 1 without optimization. This shows how adding spin as an additional design parameter in thermoelectrics research is a new and promising approach toward the quest for high-zT materials.
Spin transportMagnonSemiconductorParamagneticMagnetizationMagnetismThermoelectric powerNon-magneticAntiferromagneticOptimization...
• #### Green's function methods for single molecule junctions

We present a brief pedagogical review of theoretical Green's function methods applicable to open quantum systems out of equilibrium in general, and single molecule junctions in particular. We briefly describe experimental advances in molecular electronics, then discuss different theoretical approaches. We then focus on Green's function methods. Two characteristic energy scales governing the physics are many-body interactions within the junctions, and molecule-contact coupling. We therefore discuss weak interactions and weak coupling, as two limits that can be conveniently treated within, respectively, the standard nonequilibrium Green's function (NEGF) method and its many-body flavors (pseudoparticle and Hubbard NEGF). We argue that the intermediate regime, where the two energy scales are comparable, can in many cases be efficiently treated within the recently introduced superperturbation dual fermion approach. Finally, we review approaches for going beyond these analytically accessible limits, as embodied by recent developments in numerically exact methods based on Green's functions.
Green's functionWavefunctionPropagatorHybridizationMolecular electronicsPerturbation theoryLattice QCD sign problemDensity functional theoryDensity matrixMonte Carlo method...
• #### The high redshift SFR-M* relation is sensitive to the employed star formation rate and stellar mass indicators: Towards addressing the tension between observations and simulations

There is a severe tension between the observed star formation rate (SFR) - stellar mass (${\rm M}_{\star}$) relations reported by different authors at $z = 1-4$. In addition, the observations have not been successfully reproduced by state-of-the-art cosmological simulations which tend to predict a factor of 2-4 smaller SFRs at a fixed ${\rm M}_{\star}$. We examine the evolution of the SFR$-{\rm M}_{\star}$ relation of $z = 1-4$ galaxies using the SKIRT simulated spectral energy distributions of galaxies sampled from the EAGLE simulations. We derive SFRs and stellar masses by mimicking different observational techniques. We find that the tension between observed and simulated SFR$-{\rm M}_{\star}$ relations is largely alleviated if similar methods are used to infer the galaxy properties. We find that relations relying on infrared wavelengths (e.g. 24 ${\rm \mu m}$, MIPS - 24, 70 and 160 ${\rm \mu m}$ or SPIRE - 250, 350, 500 ${\rm \mu m}$) have SFRs that exceed the intrinsic relation by 0.5 dex. Relations that rely on the spectral energy distribution fitting technique underpredict the SFRs at a fixed stellar mass by -0.5 dex at $z \sim 4$ but overpredict the measurements by 0.3 dex at $z \sim 1$. Relations relying on dust-corrected rest-frame UV luminosities, are flatter since they overpredict/underpredict SFRs for low/high star forming objects and yield deviations from the intrinsic relation from 0.10 dex to -0.13 dex at $z \sim 4$. We suggest that the severe tension between different observational studies can be broadly explained by the fact that different groups employ different techniques to infer their SFRs.
Star formation rateGalaxyStellar massLuminositySpectral energy distributionEAGLE simulation projectStar formationStarSloan Digital Sky SurveyInfrared limit...
• #### Leptogenesis from spontaneous symmetry breaking during inflationver. 3

Symmetry breaking in the Higgs field via a non-minimal coupling to gravity or higher-dimensional interactions with the inflaton can lead to condensation at a large vacuum expectation value (VEV) during inflation. After inflation is over, the Higgs field must relax to the minimum of its effective potential, creating an era in which the CPT is effectively broken by the time-depended VEV. We show that the matter-antimatter asymmetry can be generated during this relaxation epoch.
Higgs bosonInflatonRelaxationInflationSymmetry breakingLeptogenesisReheatingHiggs fieldHiggs potentialStandard Model...