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by Prof. Carlo Beenakker04 Feb 2014 08:52

- The transformation of cold neutral intergalactic hydrogen into a highly ionized warm plasma marks the end of the cosmic dark ages and the beginning of the age of galaxies. The details of this process reflect the nature of the early sources of radiation and heat, the statistical characteristics of the large-scale structure of the Universe, the thermodynamics and chemistry of cosmic baryons, and the histories of star formation and black hole accretion. A number of massive data sets from new ground- and space-based instruments and facilities over the next decade are poised to revolutionize our understanding of primeval galaxies, the reionization photon budget, the physics of the intergalactic medium (IGM), and the fine-grained properties of hydrogen gas in the "cosmic web". In this review we survey the physics and key aspects of reionization-era modeling and describe the diverse range of computational techniques and tools currently available in this field.ReionizationIntergalactic mediumGalaxyIonizationLyman recombination continuaIonizing radiationRecombinationMean free pathIntensityRadiative transfer...
- The groundbreaking image of the black hole at the center of the M87 galaxy has raised questions at the intersection of observational astronomy and black hole physics. How well can the radius of a black hole shadow can be measured, and can this measurement be used to distinguish general relativity from other theories of gravity? We explore these questions using a simple spherical flow model in general relativity, scalar Gauss--Bonnet gravity, and the Rezzolla and Zhidenko parameterized metric. We assume an optically thin plasma with power-law emissivity in radius. Along the way we present a generalized Bondi flow as well as a piecewise-analytic model for the brightness profile of a cold inflow. We use the second moment of a synthetic image as a proxy for EHT observables and compute the ratio of the second moment to the radius of the black hole shadow. We show that corrections to this ratio from modifications to general relativity are subdominant compared to corrections to the critical impact parameter, and argue that this is generally true. We find that astrophysical model parameters are the dominant source of uncertainty in this calculation, emphasizing the importance of understanding the astrophysical model. Given a sufficiently accurate astrophysical model, however, it is possible using measurements of the black hole shadow to distinguish between general relativity and other theories of gravity.General relativityIntensityImpact parameterBlack holeAccretionTheories of gravityTelescopesEvent horizonMessier 87Modified gravity...
- We introduce the AbacusHOD model and present two applications of AbacusHOD and the AbacusSummit simulations to observations. AbacusHOD is an HOD framework written in Python that is particle-based, multi-tracer, highly generalized, and highly efficient. It is designed specifically with multi-tracer/cosmology analyses for next generation large-scale structure surveys in mind, and takes advantage of the volume and precision offered by the new state-of-the-art AbacusSummit cosmological simulations. The model is also highly customizable and should be broadly applicable to any upcoming surveys and a diverse range of cosmological analyses. In this paper, we demonstrate the capabilities of the AbacusHOD framework through two example applications. The first example demonstrates the high efficiency and the large HOD extension feature set through an analysis full-shape redshift-space clustering of BOSS galaxies at intermediate to small scales (<30Mpc/h), assessing the necessity of introducing secondary galaxy biases (assembly bias). We find strong evidence for using halo environment instead of concentration to trace secondary galaxy bias, a result which also leads to a moderate reduction to the "lensing is low" tension. The second example demonstrates the multi-tracer capabilities of the AbacusHOD package through an analysis of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) cross-correlation measurements between three different galaxy tracers, LRGs, ELGs, and QSOs. We expect the AbacusHOD framework, in combination with the AbacusSummit simulation suite, to play an important role in a simulation-based analysis of the up-coming Dark Energy Spectroscopic Instrument (DESI) datasets.Halo Occupation DistributionGalaxyHalo assembly biasVelocity biasTwo-point correlation functionBaryon Oscillation Spectroscopic SurveyRedshift spaceVirial massCosmologyMilky Way...
- This paper introduces the \emph{Simultaneous Assignment Problem}. Here, we are given an assignment problem on some of the subgraphs of a given graph, and we are looking for a heaviest assignment which is feasible when restricted to any of the assignment problems. More precisely, we are given a graph with a weight- and a capacity function on its edges and a set of its subgraphs $H_1,\dots,H_k$ along with a degree upper bound function for each of them. In addition, we are also given a laminar system on the node set with an upper bound on the degree-sum of the nodes in each set in the system. We want to assign each edge a non-negative integer below its capacity such that the total weight is maximized, the degrees in each subgraph are below the degree upper bound associated with the subgraph, and the degree-sum bound is respected in each set of the laminar system. The problem is shown to be APX-hard in the unweighted case even if the graph is a forest and $k=2$. This also implies that the Distance matching problem is APX-hard in the weighted case and that the Cyclic distance matching problem is APX-hard in the unweighted case. We identify multiple special cases when the problem can be solved in strongly polynomial time. One of these cases, the so-called locally laminar case, is a common generalization of the Hierarchical b-matching problem and the Laminar matchoid problem, and it implies that both of these problems can be solved efficiently in the weighted, capacitated case -- improving upon the most general polynomial-time algorithms for these problems. The problem can be constant approximated when $k$ is a constant, and we show that the approximation factor matches the integrality gap of a strengthened LP-relaxation for small $k$. We give improved approximation algorithms for special cases, for example, when the degree bounds are uniform or the graph is sparse.Polynomial timeOpacityGraphBipartite networkLinear optimizationNP-hard problemSparsityConvex hullLower and upperRelaxation...
- We devise a theoretical model for the optimal dynamical control of an infectious disease whose diffusion is described by the SVIR compartmental model. The control is realized through implementing social rules to reduce the disease's spread, which often implies substantial economic and social costs. We model this trade-off by introducing a functional depending on three terms: a social cost function, the cost supported by the healthcare system for the infected population, and the cost of the vaccination campaign. Using the Pontryagin's Maximum Principle, we give conditions for the existence of the optimal policy, which we characterize explicitly in three instances of the social cost function, the linear, quadratic, and exponential models, respectively. Finally, we present a set of results on the numerical solution of the optimally controlled system by using Italian data from the recent Covid--19 pandemic for the model calibration.Social distanceHamiltonianMaximum principleVaccineProgrammingHealthcare systemCalibrationConfinementSupply ChainCOVID 19...
- We propose a novel approach to obtain the growth rate of cosmic structures, $f(z)$, from the evolution of the cosmic homogeneity scale, $R_{\text{H}}(z)$. Our methodology needs two ingredients in a specific functional form: $R_{\text{H}}(z)$ data and the matter two-point correlation function today, i.e., $\xi(r, z=0)$. We use a Gaussian Process approach to reconstruct the function $R_{\text{H}}$. In the absence of suitable observational information of the matter correlation function in the local Universe, $z \simeq 0$, we assume a fiducial cosmology to obtain $\xi(r, z=0)$. For this reason, our final result turns out to be a consistency test of the cosmological model assumed. Our results show a good agreement between: (i) the growth rate $f^{R_{\text{H}}}(z)$ obtained through our approach, (ii) the $f^{\Lambda\text{CDM}}(z)$ expected in the fiducial model, and (iii) the best-fit $f(z)$ from data compiled in the literature. Moreover, using this data compilation, we perform a Gaussian Process to reconstruct the growth rate function $f^{\text{data}}(z)$ and compare it with the function $f^{R_{\text{H}}}(z)$ finding a concordance of $< \!2 \,\sigma$, a good result considering the few data available for both reconstruction processes. With more accurate $R_{\text{H}}(z)$ data, from forthcoming surveys, the homogeneity scale function might be better determined and would have the potential to discriminate between $\Lambda$CDM and alternative scenarios as a new cosmological observable.Two-point correlation functionCosmologyBaryon acoustic oscillationsPlanck missionCosmological parametersGaussian processCosmological modelLambda-CDM modelRedshift binsModified gravity...
- Within the $\Lambda$CDM cosmological model, the absolute value of Einstein's cosmological constant $\Lambda$, sometimes expressed as the gravitating mass-energy density $\rho_\Lambda$ of the physical vacuum, is a fundamental constant of nature, whose accurate measurement plays a central role in testing some proposed theories of quantum gravity. Several combinations of currently public cosmological data and an assumed flat $\Lambda$CDM cosmological model are used here to make a joint Bayesian inference on the combination of conventional parameters $\Omega_\Lambda h^2$ that corresponds to the absolute physical density $\rho_\Lambda$. In physical units, we obtain $\rho_\Lambda = \left(60.3\pm{1.3}\right)\times 10^{-31}{\rm g/cm^3}$, the most accurate constraint to date, with an absolute calibration of cosmological measurements based on CMB temperature. Significantly different values are obtained with calibrations that use a local distance scale, mainly connected to systematic differences in the value of the Hubble constant. It is suggested that future comprehensive cosmological parameter studies assuming the $\Lambda$CDM model include constraints on the vacuum density.Dark Energy SurveyCalibrationLambda-CDM modelVacuum energyPlanck missionQuantum gravityBaryon acoustic oscillationsCosmological dataCosmological constantCepheid...
- We present a comparative analysis of current observational constraints on three recently discussed alternative models for explaining the low-redshift acceleration of the universe: the so-called steady-state torsion model, the generalized coupling model, and the scale invariant model by Maeder (an example of a broader class which we also briefly study) These are compared to the traditional parameterization of Chevallier, Polarski and Linder. Each of the candidate models is studied under two different assumptions: as genuine alternatives to $\Lambda$CDM (where a new degree of freedom would be expected to explain the recent acceleration of the universe without any cosmological constant) and as parametric extensions of $\Lambda$CDM (where both a cosmological constant and the new mechanism can coexist, and the relative contributions of both are determined by the data). Our comparative analysis suggests that, from a phenomenological point of view, all such models neatly divide into two classes, with different observational consequences.Torsion tensorCosmological constantScale invarianceSteady stateChi-squared statisticDegree of freedomPlanck missionFriedmann equationsContinuity equationHubble parameter...
- Sampling-based inference techniques are central to modern cosmological data analysis; these methods, however, scale poorly with dimensionality and typically require approximate or intractable likelihoods. In this paper we describe how Truncated Marginal Neural Ratio Estimation (TMNRE) (a new approach in so-called simulation-based inference) naturally evades these issues, improving the $(i)$ efficiency, $(ii)$ scalability, and $(iii)$ trustworthiness of the inferred posteriors. Using measurements of the Cosmic Microwave Background (CMB), we show that TMNRE can achieve converged posteriors using orders of magnitude fewer simulator calls than conventional Markov Chain Monte Carlo (MCMC) methods. Remarkably, the required number of samples is effectively independent of the number of nuisance parameters. In addition, a property called \emph{local amortization} allows the performance of rigorous statistical consistency checks that are not accessible to sampling-based methods. TMNRE promises to become a powerful tool for cosmological data analysis, particularly in the context of extended cosmologies, where the timescale required for conventional sampling-based inference methods to converge can greatly exceed that of simple cosmological models such as $\Lambda$CDM. To perform these computations, we use an implementation of TMNRE via the open-source code \texttt{swyft}.InferenceCosmologyNuisance parameterCosmic microwave backgroundStatistical estimatorCosmological parametersBaryon acoustic oscillationsTraining setStatisticsPlanck mission...
- We assess the status of a wide class of WIMP dark matter (DM) models in light of the latest experimental results using the global fitting framework $\textsf{GAMBIT}$. We perform a global analysis of effective field theory (EFT) operators describing the interactions between a gauge-singlet Dirac fermion and the Standard Model quarks, the gluons and the photon. In this bottom-up approach, we simultaneously vary the coefficients of 14 such operators up to dimension 7, along with the DM mass, the scale of new physics and several nuisance parameters. Our likelihood functions include the latest data from $\mathit{Planck}$, direct and indirect detection experiments, and the LHC. For DM masses below 100 GeV, we find that it is impossible to satisfy all constraints simultaneously while maintaining EFT validity at LHC energies. For new physics scales around 1 TeV, our results are influenced by several small excesses in the LHC data and depend on the prescription that we adopt to ensure EFT validity. Furthermore, we find large regions of viable parameter space where the EFT is valid and the relic density can be reproduced, implying that WIMPs can still account for the DM of the universe while being consistent with the latest data.Dark matterEffective field theoryLarge Hadron ColliderWilson coefficientsScale of new physicsDark matter particle massWeakly interacting massive particleAnnihilation cross sectionDark matter particleStandard Model...
- Much of the baryons in galaxy groups are thought to have been driven out to large distances ($\gtrsim$$R_{500}$) by feedback, but there are few constraining observations of this extended gas. This work presents the resolved Sunyaev--Zel'dovich (SZ) profiles for a stacked sample of 10 nearby galaxy groups within the mass range log$_{10}(M_{500}[M_{\odot}]) = 13.6 -13.9$. We measured the SZ profiles using the publicly available $y$-map from the Planck Collaboration as well as our own $y$-maps constructed from more recent versions of $Planck$ data. The $y$-map extracted from the latest data release yielded a significant SZ detection out to 3 $R_{500}$. In addition, the stacked profile from these data were consistent with simulations that included AGN feedback. Our best-fit model using the latest $Planck$ data suggested a baryon fraction $\approx 5.6\%$ within $R_{500}$. This is significantly lower than the cosmic value of $\approx 16\%$, supporting the idea that baryons have been driven to large radii by AGN feedback. Lastly, we discovered a significant ($\sim 3\sigma$) "bump" feature near $\sim 2$ $R_{500}$ that is most likely the signature of internal accretion shocks.Group of galaxiesBumpingActive Galactic NucleiFull width at half maximumAGN feedbackCluster of galaxiesAccretionPlanck missionNearby galaxiesPressure profile...
- This review demonstrates the unique role of the neutrino by discussing in detail the physics of and with neutrinos. We deal with neutrino sources, neutrino oscillations, absolute masses, interactions, the possible existence of sterile neutrinos, and theoretical implications. In addition, synergies of neutrino physics with other research fields are found, and requirements to continue successful neutrino physics in the future, in terms of technological developments and adequate infrastructures, are stressed.NeutrinoNeutrino massSterile neutrinoSolar neutrinoNeutrino physicsNeutrino oscillationsNeutrino fluxAtmospheric neutrinoLiquidsEarth...
- We construct a class of 4D `yoga' (naturally relaxed) models for which the gravitational response of heavy-particle vacuum energies is strongly suppressed. The models contain three ingredients: (i) a relaxation mechanism, (ii) a very supersymmetric gravity sector coupled to matter for which supersymmetry is non-linearly realised, and (iii) an accidental approximate scale invariance expressed through the presence of a low-energy dilaton supermultiplet. All three are common in higher-dimensional and string constructions and although none suffices on its own, taken together they can dramatically suppress the net vacuum-energy density. The dilaton's {\it vev}~$\tau$ determines the weak scale $M_W \sim M_p/\sqrt\tau$. We compute the potential for $\tau$ and find it can be stabilized in a local de Sitter minimum at sufficiently large field values to explain the electroweak hierarchy, doing so using input parameters no larger than $O(60)$ because the relevant potential arises as a rational function of $\ln\tau$. The de Sitter vacuum energy at the minimum is order $c\, M_W^8 \propto 1/\tau^4$, with $c \ll O(M_W^{-4})$. We discuss how to achieve $c \sim 1/M_p^4$ as required by observations. Scale invariance implies the dilaton couples to matter like a Brans-Dicke scalar with dangerously large coupling yet because it comes paired with an axion it can evade bounds through the novel screening mechanism described in {\tt ArXiV:2110.10352}. Cosmological axio-dilaton evolution predicts a natural quintessence model for Dark Energy, whose evolution can realize recent proposals to resolve the Hubble tension, and whose axion contributes to Dark Matter. We summarize inflationary implications and some remaining challenges, including the unusual supersymmetry breaking regime used and the potential for UV completions of our approach.DilatonAxionScale invarianceStandard ModelSupersymmetrySupersymmetricSupergravityGravitinoCosmologyVacuum energy...
- The U$\mu\nu$SSM is a $U(1)'$ extension of the $\mu\nu$SSM supersymmetric model, where baryon-number-violating operators as well as explicit mass terms are forbidden, and the potential domain wall problem is avoided. The gauge anomaly-cancellation conditions impose the presence of exotic quark superfields in the spectrum of U$\mu\nu$SSM models, and allow the presence of several singlet superfields under the standard model gauge group, in addition to the right-handed neutrino superfields. The gauge structure implies an additional discrete $Z_2$ symmetry in the superpotential, ensuring the stability of a singlet which behaves as WIMP dark matter without invoking $R$-parity. We analyze this novel possibility in detail, using the fermionic component of the singlet as the dark matter candidate. In particular, we compute its amount of relic density via $Z'$, Higgs-right sneutrino and dark matter mediated annihilations, and its potential signals in dark matter direct detection experiments. The constraints on the parameter space due to $Z'$ direct searches at the LHC are imposed in the analysis, as well as those from the hadronization inside the detector of the exotic quarks. Large regions of the parameter space turn out to be in the reach of the upcoming Darwin experiment.SuperfieldDark matterWeakly interacting massive particleSuperpotentialStandard ModelSterile neutrinoLaboratory dark matter searchAnomaly cancellationNeutrinoLarge Hadron Collider...
- Planning for the development of a 3rd generation global gravitational-wave detector array is a multifaceted and complex effort that will necessarily need a high level of community input. Interfacing to extant and new stakeholders in the broader scientific constituencies is necessary to keep them aware of the activities taking place in the ground-based gravitational-wave community and receive input to inform and evolve the planning. In this report, we present the approaches GWIC and gravitational-wave collaborations and projects should consider taking to engage with broader community. This report is the fifth in a six part series of reports by the GWIC 3G Subcommittee: i) Expanding the Reach of Gravitational Wave Observatories to the Edge of the Universe, ii) The Next Generation Global Gravitational Wave Observatory: The Science Book, iii) 3G R&D: R&D for the Next Generation of Ground-based Gravitational Wave Detectors, iv) Gravitational Wave Data Analysis: Computing Challenges in the 3G Era, v) Future Ground-based Gravitational-wave Observatories: Synergies with Other Scientific Communities (this report), and vi) An Exploration of Possible Governance Models for the Future Global Gravitational-Wave Observatory Network.Gravitational waveObservatoriesGravitational wave detectorMultidimensional ArrayLoschmidt echoUniverseNetworks...
- The first direct detection of gravitational waves emitted from a pair of merging black holes in 2015 has been heralded as one of most significant scientific breakthroughs in physics and astronomy of the 21st century. Motivated by the tremendous scientific opportunities now opened by gravitational-wave observatories and recognizing that to fully exploit the new field will require new observatories that may take 15 to 20 years from conception until operations begin, the Gravitational Wave International Committee (GWIC) convened a subcommittee to examine the path to build and operate a network of future ground-based observatories, capable of extending the observational GW horizon well beyond that currently attainable with the current generation of detectors. This report is the first in a six part series of reports by the GWIC 3G Subcommittee: i) Expanding the Reach of Gravitational Wave Observatories to the Edge of the Universe (this report), ii) The Next Generation Global Gravitational Wave Observatory: The Science Book, iii) 3G R&D: R&D for the Next Generation of Ground-based Gravitational Wave Detectors, iv) Gravitational Wave Data Analysis: Computing Challenges in the 3G Era, v) Future Ground-based Gravitational-wave Observatories: Synergies with Other Scientific Communities, and vi) An Exploration of Possible Governance Models for the Future Global Gravitational-Wave Observatory Network.Gravitational waveObservatoriesGravitational wave astronomyGravitational wave detectorHorizonBlack holeLoschmidt echoUniverseNetworksAstronomy...
- In this work we present a summary of recent studies on the effects of elastic self interactions in the evolution of Warm Dark Matter models (WDM), focusing on structure formation and the evolution of cosmological perturbations. We pay special attention to a particular class of sterile neutrino WDM known as $\nu$MSM and provide examples for the case of vector field self interactions. We calculate the effects of assuming self interacting dark matter in X-Ray astrophysical observations, in the formation of fermionic DM halos in (quasi) equilibrium states and in the evolution of DM perturbations in the early universe, assuming particle masses between $\mathcal{O}(1-100)$ keV. In the latter topic, we perform simulations using a modification to the public Boltzmann solver CLASS and compare our results with observations. We find self interactions to be an interesting addition to WDM models, which can alleviate tensions both present in standard CDM cosmology and regarding WDM itself, as well as provide an interesting avenue for DM halo formation.Warm dark matterWDM particlesDark matter haloStructure formationSterile neutrinoCosmological perturbationsParticle massSelf-interacting dark matterLambda-CDM modelDark matter model...
- We present an analytic study of the density fluctuation of a Newtonian self-gravity fluid in the expanding universe with $\Omega_\Lambda+\Omega_m=1$, which extends our previous work in the static case. By use of field theory techniques, we obtain the nonlinear, hyperbolic equation of 2-pt correlation function $\xi$ of perturbation. Under the Zel'dolvich approximation the equation becomes an integro-differential equation and contains also the 3-pt and 4-pt correlation functions. By adopting the Groth-Peebles and Fry-Peebles ansatz, the equation becomes closed, contains a pressure term and a delta source term which were neglected in Davis and Peebles' milestone work. The equation has three parameters of fluid: the particle mass $m$ in the source, the overdensity $\gamma$, and the sound speed $c_s$. We solve only the linear equation and apply to the system of galaxies. We assume two models of $c_s$ and, take an initial power spectrum at a redshift $z=7$, which inherits the relevant imprint from the spectrum of baryon acoustic oscillations at the decoupling. The solution $\xi({\bf r}, z)$ is growing during expansion, and contains $100$Mpc periodic bumps at large scales, and a main mountain (a global maximum with $\xi \propto r^{-1}$) at small scales $r\lesssim 50$Mpc. The profile of $\xi$ agrees with the observed ones from galaxy and quasar surveys. The bump separation is given by the Jeans length $\lambda_J$ as the correlation scale, also modified by $\gamma$ and $c_s$. The main mountain is largely generated by the source $\propto m$ as the clustering scale. Since the outcome is affected by the initial condition and the parameters as well, it is hard to infer the imprint of baryon acoustic oscillations accurately. The difficulties with the sound horizon as a distance ruler are pointed out.GalaxyBumpingTwo-point correlation functionBaryon acoustic oscillationsExpanding universeSound horizonSpeed of soundJeans lengthPrimordial density perturbationQuasar...
- Subsonic, compressive turbulence transfers energy to cosmic rays (CRs), a process known as non-resonant reacceleration. It is often invoked to explain observed ratios of primary to secondary CRs at $\sim \rm GeV$ energies, assuming wholly diffusive CR transport. However, such estimates ignore the impact of CR self-confinement and streaming. We study these issues in stirring box magnetohydrodynamic (MHD) simulations using Athena++, with field-aligned diffusive and streaming CR transport. For diffusion only, we find CR reacceleration rates in good agreement with analytic predictions. When streaming is included, reacceleration rates depend on plasma $\beta$. Due to streaming-modified phase shifts between CR and gas variables, they are slower than canonical reacceleration rates in low-$\beta$ environments like the interstellar medium (ISM) but remain unchanged in high-$\beta$ environments like the intracluster medium (ICM). We also quantify the streaming energy loss rate in our simulations. For sub-Alfv\'{e}nic turbulence, it is resolution-dependent (hence unconverged in large scale simulations) and heavily suppressed -- by an order of magnitude -- compared to the isotropic loss rate $v_{A} \cdot \nabla P_{\rm CR} / P_{\rm CR} \sim v_{A}/L_{0}$, due to misalignment between the mean field and isotropic CR gradients. Counterintuitively, and unlike acceleration efficiencies, CR losses are almost independent of magnetic field strength over $\beta \sim 1-100$ and are, therefore, not the primary factor behind lower acceleration rates when streaming is included. While this paper is primarily concerned with how turbulence affects CRs, in a follow-up paper (Bustard and Oh, in prep), we consider how CRs affect turbulence by diverting energy from the MHD cascade, altering the pathway to gas heating and steepening the turbulent power spectrum.Cosmic rayTurbulenceEddyInterstellar mediumDiffusion coefficientMagnetohydrodynamicsIntra-cluster mediumCircumgalactic mediumMach numberConfinement...
- Energy dissipation in collisionless plasmas is a longstanding fundamental physics problem. Although it is well known that magnetic reconnection and turbulence are coupled and transport energy from system-size scales to sub-proton scales, the details of the energy distribution and energy dissipation channels remain poorly understood. Especially, the energy transfer and transport associated with three dimensional (3D) small-scale reconnection that occurs as a consequence of a turbulent cascade is unknown. We use an explicit fully kinetic particle-in-cell code to simulate 3D small scale magnetic reconnection events forming in anisotropic and Alfv\'enic decaying turbulence. We identify a highly dynamic and asymmetric reconnection event that involves two reconnecting flux ropes. We use a two-fluid approach based on the Boltzmann equation to study the spatial energy transfer associated with the reconnection event and compare the power density terms in the two-fluid energy equations with standard energy-based damping, heating and dissipation proxies. Our findings suggest that the electron bulk flow transports thermal energy density more efficiently than kinetic energy density. Moreover, in our turbulent reconnection event, the energy-density transfer is dominated by plasma compression. This is consistent with turbulent current sheets and turbulent reconnection events, but not with laminar reconnection.Magnetic reconnectionDissipationTurbulenceSolar windParticle-in-cellElectron pressureBoltzmann transport equationBulk flowCollisionless plasmaVelocity distribution function...
- It is known that the large-scale structure (LSS) mapped by a galaxy redshift survey is subject to distortions by galaxies' peculiar velocities. Besides the signatures generated in common N-point statistics, such as the anisotropy in the galaxy 2-point correlation function, the peculiar velocities also induce distinct features in LSS's morphological properties, which are fully described by four Minkowski functionals (MFs), i.e., the volume, surface area, integrated mean curvature and Euler characteristic (or genus). In this work, by using large suite of N-body simulations, we present and analyze these important features in the MFs of LSS on both (quasi-)linear and non-linear scales, with a focus on the latter. We also find the MFs can give competitive constraints on cosmological parameters compared to the power spectrum, probablly due to the non-linear information contained. For galaxy number density similar to the DESI BGS galaxies, the constraint on $\sigma_8$ from the MFs with one smoothing scale can be better by $\sim 50\%$ than from the power spectrum. These findings are important for the cosmological applications of MFs of LSS, and probablly open up a new avenue for studying the peculiar velocity field itself.Minkowski functionalLarge scale structurePeculiar velocityRedshift spaceGalaxyStatisticsMean curvatureReal spaceLine of sightEuler characteristic...
- We investigate the effects of magnetic field configurations on the ionization rate by cosmic rays in protoplanetary disks. First, we consider cosmic-ray propagation from the interstellar medium (ISM) to the protoplanetary disks and showed that the cosmic-ray density around the disk should be 4 times lower than the ISM value. Then, we compute the attenuation of cosmic rays in protoplanetary disks. The magnetic fields in the disk are stretched to the azimuthal directions, and cosmic rays need to detour while propagating to the midplane. We show that the detouring effectively enhances the column density by about two orders of magnitudes. In the case of the disk around IM lup, this increases the ionization rate over an order of magnitude for $r\gtrsim\,100$ au. On the other hand, for $r\lesssim\,100$ au, the cosmic rays are shielded at the disk midplane while the ionization rate is also enhanced at $z\sim\,2H$. Our results are consistent with the recent ALMA observation that indicates the radial gradient in the cosmic-ray ionization rate. The elevated ionization rate in the outer radii of disks may activate the magnetorotational instability that was thought to be suppressed due to ambipolar diffusion. These results will have a strong influence on the dynamical and chemical evolutions of protoplanetary disks.Cosmic rayIonizationProtoplanetary diskInterstellar mediumTurbulenceShearedMagnetorotational instabilityCosmic ray fluxAtacama Large Millimeter ArrayMolecular cloud...
- MeerKAT's large number of antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900-1670 MHz) observations of 115 galaxy clusters, observed for $\sim$6-10 hours each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at $\sim$8" resolution, and enhanced spectral and polarisation image cubes at $\sim$8" and 15" resolutions. Typical sensitivities for the full-resolution MGCLS image products are $\sim$3-5 {\mu}Jy/beam. The basic cubes are full-field and span 4 deg^2. The enhanced products consist of the inner 1.44 deg^2 field of view, corrected for the primary beam. The survey is fully sensitive to structures up to $\sim$10' scales and the wide bandwidth allows spectral and Faraday rotation mapping. HI mapping at 209 kHz resolution can be done at $0<z<0.09$ and $0.19<z<0.48$. In this paper, we provide an overview of the survey and DR1 products, including caveats for usage. We present some initial results from the survey, both for their intrinsic scientific value and to highlight the capabilities for further exploration with these data. These include a primary beam-corrected compact source catalogue of $\sim$626,000 sources for the full survey, and an optical/infrared cross-matched catalogue for compact sources in Abell 209 and Abell S295. We examine dust unbiased star-formation rates as a function of clustercentric radius in Abell 209 and present a catalogue of 99 diffuse cluster sources (56 are new), some of which have no suitable characterisation. We also highlight some of the radio galaxies which challenge current paradigms and present first results from HI studies of four targets.Radio galaxyGalaxyMeerKATRadio sourcesLuminosityCluster of galaxiesStar formationStar formation rateDiffuse emissionActive Galactic Nuclei...
- Gamma-ray bursts (GRBs) have long been proposed as a complementary probe to type Ia supernovae (SNe Ia) and cosmic microwave background to explore the expansion history of the high-redshift universe, mainly because they are bright enough to be detected at greater distances. Although they lack definite physical explanations, many empirical correlations between GRB isotropic energy/luminosity and some directly detectable spectral/temporal properties have been proposed to make GRBs standard candles. Since the observed GRB rate falls off rapidly at low redshifts, thus preventing a cosmology independent calibration of these correlations. In order to avoid the circularity problem, SN Ia data are usually used to calibrate the luminosity relations of GRBs in the low redshift region (limited by the redshift range for SN Ia sample), and then extrapolate it to the high redshift region. This approach is based on the assumption of no redshift evolution for GRB luminosity relations. In this work, we suggest the use a complete quasar sample in the redshift range of $0.5<z<5.5$ to test such an assumption. We divide the quasar sample into several sub-samples with different redshift bins, and use each sub-sample to calibrate the isotropic $\gamma$-ray equivalent energy of GRBs in relevant redshift bins. By fitting the newly calibrated data, we find strong evidence that the most commonly used Amati relation between spectral peak energy and isotropic-equivalent radiated energy shows no, or marginal, evolution with redshift. Indeed, at different redshifts, the coefficients in the Amati relation could have a maximum variation of 0.93\% at different redshifts, and there could be no coincidence in the range of 1$\sigma$.Gamma ray burstQuasarLuminositySupernova Type IaHubble diagramCosmologyLuminosity distanceCalibrationRedshift binsStandard candle...
- This is a draft of the first 7 chapters of a textbook/monograph that presents computability theory using string diagrams. The introductory chapters have been taught as graduate and undergraduate courses and evolved through 8 years of lecture notes. The later chapters contain new ideas and results about categorical computability and some first steps into computable category theory. The underlying categorical view of computation is based on monoidal categories with program evaluators, called *monoidal computers*. This categorical structure can be viewed as a single-instruction diagrammatic programming language called Run, whose only instruction is called RUN.ProgrammingProgramming LanguageIsomorphismTransformerCountingBoilingEngineeringArithmeticSoftwareHyperfunction...
- We use N-body simulations to model the tidal evolution of dark matter-dominated dwarf spheroidal galaxies embedded in cuspy Navarro-Frenk-White subhalos. Tides gradually peel off stars and dark matter from a subhalo, trimming it down according to their initial binding energy. This process strips preferentially particles with long orbital times, and comes to an end when the remaining bound particles have crossing times shorter than a fraction of the orbital time at pericentre. The properties of the final stellar remnant thus depend on the energy distribution of stars in the progenitor subhalo, which in turn depends on the initial density profile and radial segregation of the initial stellar component. The stellar component may actually be completely dispersed if its energy distribution does not extend all the way to the subhalo potential minimum, although a bound dark remnant may remain. These results imply that 'tidally-limited' galaxies, defined as systems whose stellar components have undergone substantial tidal mass loss, neither converge to a unique structure nor follow a single tidal track, as claimed in earlier work. On the other hand, tidally limited dwarfs do have characteristic sizes and velocity dispersions that trace directly the characteristic radius ($r_{max}$) and circular velocity ($V_{max}$) of the subhalo remnant. This result places strong upper limits on the size of satellites whose unusually low velocity dispersions are often ascribed to tidal effects. In particular, the large size of kinematically-cold 'feeble giant' satellites like Crater 2 or Antlia 2 cannot be explained as due to tidal effects alone in the Lambda Cold Dark Matter scenario.Dark matter subhaloNavarro-Frenk-White profileDark matterVelocity dispersionStarGalaxyTidesLambda-CDM modelHalf-light radiusCircular velocity...
- The interstellar medium (ISM) of star-forming galaxies is magnetized and turbulent. Cosmic rays (CRs) propagate through it, and those with energies from $\sim\,\rm{GeV} - \rm{TeV}$ are likely subject to the streaming instability, whereby the wave damping processes balances excitation of resonant ionic Alfv\'en waves by the CRs, reaching an equilibrium in which the propagation speed of the CRs is very close to the local ion Alfv\'en velocity. The transport of streaming CRs is therefore sensitive to ionic Alfv\'en velocity fluctuations. In this paper we systematically study these fluctuations using a large ensemble of compressible MHD turbulence simulations. We show that for sub-Alfv\'enic turbulence, as applies for a strongly magnetized ISM, the ionic Alfv\'en velocity probability density function (PDF) is determined solely by the density fluctuations from shocked gas forming parallel to the magnetic field, and we develop analytical models for the ionic Alfv\'en velocity PDF up to second moments. For super-Alfv\'enic turbulence, magnetic and density fluctuations are correlated in complex ways, and these correlations as well as contributions from the magnetic fluctuations sets the ionic Alfv\'en velocity PDF. We discuss the implications of these findings for underlying "macroscopic" diffusion mechanisms in CRs undergoing the streaming instability, including modeling the macroscopic diffusion coefficient for the parallel transport in sub-Alfv\'enic plasmas. We also describe how, for highly-magnetized turbulent gas, the gas density PDF, and hence column density PDF, can be used to access information about ionic Alfv\'en velocity structure from observations of the magnetized ISM.TurbulenceCosmic rayInterstellar mediumAlfven velocityStatisticsVelocity fluctuationsIonizationCovarianceTwo-stream instabilityDiffusion coefficient...
- Budding allows virus replication and macromolecular secretion in cells. It involves the formation of a bud, i.e. an outgrowth from the cell membrane that evolves into an envelope. The largest energetic barrier to bud formation is membrane deflection and is trespassed primarily thanks to nucleocapsid-membrane adhesion. Transmembrane proteins (TPs), which later form the virus ligands, are the main promotors of adhesion and can accommodate membrane bending thanks to an induced spontaneous curvature. Adhesive TPs must diffuse across the membrane from remote regions to gather on the bud surface, thus, diffusivity controls the kinetics. This paper proposes a simple model to describe diffusion-mediated budding unraveling important size limitations and size-dependent kinetics. The predicted optimal virion radius, giving the fastest budding, is validated against experiments for Coronavirus, HIV, Flu, and Hepatitis. Assuming exponential replication of virions and hereditary size, the model can predict the size distribution of a virus population. This is verified against experiments for SARS-CoV-2. All the above comparisons rely on the premise that budding poses the tightest size constraint. This is true in most cases, as demonstrated in this paper, where the proposed model is extended to describe virus infection via receptor- and clathrin-mediated endocytosis, and via membrane fusion.MembraneAdhesionDiffusion coefficientCurvatureProtein...
- We perform a statistical clustering analysis of upper main-sequence stars in the Large Magellanic Cloud (LMC) using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds. We map over 2500 young stellar structures at 15 significance levels across ~120 square degrees centred on the LMC. The structures have sizes ranging from a few parsecs to over 1 kpc. We find that the young structures follow power-law size and mass distributions. From the perimeter-area relation, we derive a perimeter-area dimension of 1.44+-0.20. From the mass-size relation and the size distribution, we derive two-dimensional fractal dimensions of 1.50+-0.10 and 1.61+-0.20, respectively. We find that the surface density distribution is well-represented by a lognormal distribution. We apply the Larson relation to estimate the velocity dispersions and crossing times of these structures. Our results indicate that the fractal nature of the young stellar structures has been inherited from the gas clouds from which they form and that this architecture is generated by supersonic turbulence. Our results also suggest that star formation in the LMC is scale-free from 10 pc to 700 pc.Large Magellanic CloudStar formationStarStellar structureFractal dimensionVariational Monte CarloOf starsTurbulenceFractalGalaxy...
- High-energy radiation of young pulsar wind nebulae (PWNe) is known to be variable. This is most prominently exemplified by the Crab nebula which can undergo both rapid brightenings and dimmings. Two pulsars in the Large Magellanic Cloud, PSR J0540-6919 and PSR J0537-6910 are evolutionally very close to Crab, so one may expect the same kind of variability from the PWNe around them as from the Crab nebula. In this work we search for variability in these PWNe in gamma rays using the data from the Fermi Large Area Telescope in the range 100 MeV-10 GeV collected from August 2008 to December 2021. We construct light curves of these sources in the three bands, 100-300 MeV, 300-1000 MeV and 1-10 GeV with the one week time resolution. We find evidence of flaring activity in all the bands, in contrast with Crab, where no flares at $E>1$ GeV were observed. Analysis of the flaring episode in the 100-300 and 300-1000 MeV bands indicates that the flux of one of the PWNe could grew by a factor of $\approx 5-10$. We are not confident about which of the two PWNe flared because of their proximity in the sky. However, in the 1-10 GeV band where the angular resolution of the LAT is better, we find several episodes of enhanced brightness in both the PWNe. We check possible contaminants which could be responsible for the observed variability, but find their contribution not to be relevant.PulsarPulsar wind nebulaLight curveLarge Magellanic CloudCrab NebulaTest statisticGamma-ray flaresFERMI telescopeBlazarSupernova remnant...
- We study several flavors of homotopy coherent nerves for enriched categories, in the form of right Quillen functors valued in simplicial objects. In particular, we extract explicit models for the (Segal) Reedy-injective fibrant replacement of the ordinary nerve of an enriched category. In the case of interest of categories enriched over complete Segal $\Theta_{n-1}$-spaces, we also provide an explicit completion for its ordinary nerve. This is then used to obtain a direct Quillen equivalence between categories enriched over complete Segal $\Theta_{n-1}$-spaces and complete Segal $\Theta_n$-spaces.Model structureEnriched categoryFibrationMonomorphismIsomorphismSegal spaceModel categoryKan extensionProgrammingCompleteness...
- We report the discovery of the bright reflected emission component in the super-Eddington state of the ULX pulsar Swift J0243.6+6124, based on the NuSTAR observations of the source during its 2017 outburst. The flux of the reflected emission is weakly variable over the pulsar phase while the direct emission shows significantly larger pulsation amplitude. We propose that in this system the neutron star finds itself in the centre of the well formed by the inner edge of the geometrically thick super-Eddington accretion disc truncated by the magnetic field of the pulsar. The aspect ratio of the well is H/R \sim 1. The inner edge of the truncated disc is continuously illuminated by the emission of the accretion column giving rise to the weakly variable reflected emission. As the neutron star rotates, its emission sweeps through the line of sight, giving rise to the pulsating direct emission. From Doppler broadening of the iron line, we measure the truncation radius of the accretion disc \sim 50 R_g. The inferred dipole component of the magnetic field is consistent with previous estimates favouring a not very strong field. The uniqueness of this system is determined by its moderately super-Eddington accretion rate and the moderate magnetic field so that the inner edge of the truncated geometrically thick accretion disc is seen from the neutron star at a large solid angle.PulsarAccretion diskNeutron starDirect emissionOptical burstsLuminositySuper-Eddington accretionAccretionMass accretion rateEquivalent width...
- There has been a surge of recent interest in learning representations for graph-structured data. Graph representation learning methods have generally fallen into three main categories, based on the availability of labeled data. The first, network embedding (such as shallow graph embedding or graph auto-encoders), focuses on learning unsupervised representations of relational structure. The second, graph regularized neural networks, leverages graphs to augment neural network losses with a regularization objective for semi-supervised learning. The third, graph neural networks, aims to learn differentiable functions over discrete topologies with arbitrary structure. However, despite the popularity of these areas there has been surprisingly little work on unifying the three paradigms. Here, we aim to bridge the gap between graph neural networks, network embedding and graph regularization models. We propose a comprehensive taxonomy of representation learning methods for graph-structured data, aiming to unify several disparate bodies of work. Specifically, we propose a Graph Encoder Decoder Model (GRAPHEDM), which generalizes popular algorithms for semi-supervised learning on graphs (e.g. GraphSage, Graph Convolutional Networks, Graph Attention Networks), and unsupervised learning of graph representations (e.g. DeepWalk, node2vec, etc) into a single consistent approach. To illustrate the generality of this approach, we fit over thirty existing methods into this framework. We believe that this unifying view both provides a solid foundation for understanding the intuition behind these methods, and enables future research in the area.GraphEmbeddingGraph Neural NetworkRegularizationGraph embeddingTaxonomyManifoldRandom walkGraph ConvolutionAttention...
- We give a pedagogical introduction to quantum anomalies, how they are calculated using various methods, and why they are important in condensed matter theory. We discuss axial, chiral, and gravitational anomalies as well as global anomalies. We illustrate the theory with examples such as quantum Hall liquids, Fermi liquids, Weyl semi-metals, topological insulators and topological superconductors. The required background is basic knowledge of quantum field theory, including fermions and gauge fields, and some familiarity with path integral and functional methods. Some knowledge of topological phases of matter is helpful, but not necessary.Quantum anomalyTime-reversal symmetryGauge fieldManifoldChern-Simons termEffective actionHamiltonianPartition functionQuantum Hall EffectSpectral flow...
- The Magellanic Clouds, two dwarf galaxy companions to the Milky Way, are among the Fermi Large Area Telescope (LAT) brightest gamma-ray sources. Aiming at a comprehensive modeling of the non-thermal electromagnetic and neutrino emission in both Clouds, we self-consistently model the radio and gamma-ray spectral energy distribution from their disks based on recently published Murchison Widefield Array and Fermi/LAT data. All relevant radiative processes involving relativistic and thermal electrons (synchrotron, Compton scattering, and bremsstrahlung) and relativistic protons (neutral-pion decay following interaction with thermal protons) are considered, using exact emission formulae. Our joint spectral analyses indicate that radio emission in the Clouds has both primary and secondary electron synchrotron and thermal bremsstrahlung origin, whereas gamma rays originate mostly from neutral-pion decay with some contributions from relativistic bremsstrahlung and Compton scattering off starlight. The proton spectra in both galaxies are modeled as power laws in energy with similar spectral indices, ~2.4, and energy densities, ~1 eV/cm3. The predicted 0.1-10 GeV neutrino flux is too low for detection by current and upcoming experiments. Our analyses confirm earlier suggestions of a largely hadronic origin of the gamma-ray emission in both Magellanic Clouds.Magellanic CloudsSynchrotronSpectral energy distributionBremsstrahlungGalaxyStar formationCosmic microwave backgroundSynchrotron radiationCosmic rayExtragalactic background light...
- Finding high-quality solutions to mixed-integer linear programming problems (MILPs) is of great importance for many practical applications. In this respect, the refinement heuristic local branching (LB) has been proposed to produce improving solutions and has been highly influential for the development of local search methods in MILP. The algorithm iteratively explores a sequence of solution neighborhoods defined by the so-called local branching constraint, namely, a linear inequality limiting the distance from a reference solution. For a LB algorithm, the choice of the neighborhood size is critical to performance. In this work, we study the relation between the size of the search neighborhood and the behavior of the underlying LB algorithm, and we devise a leaning based framework for predicting the best size for the specific instance to be solved. Furthermore, we have also investigated the relation between the time limit for exploring the LB neighborhood and the actual performance of LB scheme, and devised a strategy for adapting the time limit. We computationally show that the neighborhood size and time limit can indeed be learned, leading to improved performances and that the overall algorithm generalizes well both with respect to the instance size and, remarkably, across instances.RegressionMachine learningOptimizationGraph Neural NetworkStatisticsReinforcement learningMarkov decision processLinear optimizationGraphTraining set...
- We present the results of a broadband (0.5-78 keV) X-ray spectral study of the persistent Galactic black hole X-ray binary GRS 1758-258 observed simultaneously by Swift and NuSTAR. Fitting with an absorbed power-law model revealed a broad Fe line and reflection hump in the spectrum. We used different flavours of the relativistic reflection model for the spectral analysis. All models indicate the spin of the black hole in GRS 1758-258 is >0.92. The source was in the low hard state during the observation, with the hot electron temperature of the corona estimated to be kT$_e$ ~ 140 keV. The black hole is found to be accreting at ~1.5 % of the Eddington limit during the observation, assuming the black hole mass of 10 $M_{\odot}$ and distance of 8 kpc.Black holeNuclear Spectroscopic Telescope ArraySpectral analysisCoronaAccretion diskX-ray spectroscopyFe abundanceBlack hole candidateFlavourX-ray binary...
- Faraday rotation studies of distant radio sources can constrain the evolution and the origin of cosmic magnetism. We use data from the LOFAR Two Metre Sky Survey: Data Release 2 (LoTSS DR2) to study the dependence of the Faraday rotation measure (RM) on redshift. By focusing on radio sources that are close in terms of their projection on the sky, but physically unrelated (random pairs), we measure the RM difference, $\Delta$RM, between the two sources. Thus, we isolate the extragalactic contribution to $\Delta$RM from other contributions. We present a statistical analysis of the resulting sample of random pairs and find a median absolute RM difference |$\Delta$RM| $ = (1.79 \pm 0.09)$ rad/m$^{2}$ , with |$\Delta$RM| uncorrelated both with respect to the redshift difference of the pair and the redshift of the nearer source, and a median excess of random pairs over physical pairs of $(1.65 \pm 0.10)$ rad/m$^{2}$. We seek to reproduce this result with Monte Carlo simulations assuming a non vanishing seed cosmological magnetic field and a redshift evolution of the comoving magnetic field strength that varies as $1/(1 + z)^{\gamma}$. We find the best fitting results $B_0 \equiv B_{\rm comoving}(z = 0) \lesssim (2.0 \pm 0.2)$ nG and $\gamma \lesssim 4.5 \pm 0.2$ that we conservatively quote as upper limits due to an unmodelled but non vanishing contribution of local environments to the RM difference. A comparison with cosmological simulations shows our results to be incompatible with primordial magnetogenesis scenarios with uniform seed fields of order nG.Extragalactic magnetic fieldRadio sourcesFaraday rotationMagnetic field strengthMagnetogenesisSky surveysMagnetismSimulations of structure formationCosmological magnetic fieldMonte Carlo method...
- Many gamma-ray bursts (GRBs) have been observed from radio wavelengths, and a few at very-high energies (VHEs, > 100GeV). The HAWC gamma-ray observatory is well suited to study transient phenomena at VHEs due to its large field of view and duty cycle. These features allow for searches of VHE emission and can probe different model assumptions of duration and spectra. In this paper, we use data collected by HAWC between December 2014 and May 2020 to search for emission in the energy range from 80 to 800 GeV coming from a sample 47 short GRBs that triggered the Fermi, Swift and Konus satellites during this period. This analysis is optimized to search for delayed and extended VHE emission within the first 20 s of each burst. We find no evidence of VHE emission, either simultaneous or delayed, with respect to the prompt emission. Upper limits (90% confidence level) derived on the GRB fluence are used to constrain the synchrotron self-Compton forward-shock model. Constraints for the interstellar density as low as $10^{-2}$ cm$^{-3}$ are obtained when assuming z=0.3 for bursts with the highest keV-fluences such as GRB 170206A and GRB 181222841. Such a low density makes observing VHE emission mainly from the fast cooling regime challenging.Gamma ray burstHigh Altitude Water CherenkovCoolingLight curvePrompt emissionSynchrotron Self-Compton radiationForward shockLorentz factorZenithVery high energy gamma-ray...
- Different properties of dark matter haloes, including growth rate, concentration, interaction history, and spin, correlate with environment in unique, scale-dependent ways. While these halo properties are not directly observable, galaxies will inherit their host haloes' correlations with environment. In this paper, we show how these characteristic environmental signatures allow using measurements of galaxy environment to constrain which dark matter halo properties are most tightly connected to observable galaxy properties. We show that different halo properties beyond mass imprint distinct scale-dependent signatures in both the galaxy two-point correlation function and the distribution of distances to galaxies' $k$th nearest neighbours, with features strong enough to be accessible even with low-resolution (e.g., grism) spectroscopy at higher redshifts. As an application, we compute observed two-point correlation functions for galaxies binned by half-mass radius at $z=0$ from the Sloan Digital Sky Survey, showing that classic galaxy size models (i.e., galaxy size being proportional to halo spin) as well as other recent proposals show significant tensions with observational data. We show that the agreement with observed clustering can be improved with a simple empirical model in which galaxy size correlates with halo growth.GalaxyTwo-point correlation functionStellar massSloan Digital Sky SurveyRankVirial massHalo concentrationsDisk galaxyDark matter haloMilky Way...
- The holographic principle suggests that the Hilbert space of quantum gravity is locally finite-dimensional. Motivated by this point-of-view, and its application to the observable Universe, we introduce a set of numerical and conceptual tools to describe scalar fields with finite-dimensional Hilbert spaces, and to study their behaviour in expanding cosmological backgrounds. These tools include accurate approximations to compute the vacuum energy of a field mode $\mathbf{k}$ as a function of the dimension $d_{\mathbf{k}}$ of the mode Hilbert space, as well as a parametric model for how that dimension varies with $|\mathbf{k}|$. We show that the maximum entropy of our construction momentarily scales like the boundary area of the observable Universe for some values of the parameters of that model. And we find that the maximum entropy generally follows a sub-volume scaling as long as $d_{\mathbf{k}}$ decreases with $|\mathbf{k}|$. We also demonstrate that the vacuum energy density of the finite-dimensional field is dynamical and decays between two constant epochs in our fiducial construction. These results rely on a number of non-trivial modelling choices, but our general framework may serve as a starting point for future investigations of the impact of finite-dimensionality of Hilbert space on cosmological physics.Vacuum energyHamiltonianScalar fieldEntropyError functionDegree of freedomQubitHarmonic oscillatorQuantum theoryHolographic principle...
- The late-time effect of primordial non-Gaussianity offers a window into the physics of inflation and the very early Universe. In this work we study the consequences of a particular class of primordial non-Gaussianity that is fully characterized by initial density fluctuations drawn from a non-Gaussian probability density function, rather than by construction of a particular form for the primordial bispectrum. We numerically generate multiple realisations of cosmological structure and use the late-time matter power spectrum, bispectrum and trispectrum to determine the effect of these modified initial conditions. We show that the initial non-Gaussianity has only a small imprint on the first three polyspectra, when compared to a standard Gaussian cosmology. Furthermore, some of our models present an interesting scale-dependent deviation from the Gaussian case in the bispectrum and trispectrum, although the signal is at most at the percent level. The majority of our models are consistent with CMB constraints on the trispectrum, while the others are only marginally excluded. Finally, we discuss further possible extensions of our study.BispectrumNon-GaussianityTrispectrumPrimordial Non-GaussianitiesRAMSES codeLarge scale structureTwo-point correlation functionStatisticsInflationN-body simulation...
- We numerically and analytically explore the background cosmological dynamics of multifield dark energy with highly non-geodesic or "spinning" field-space trajectories. These extensions of standard single-field quintessence possess appealing theoretical features and observable differences from the cosmological standard model. At the level of the cosmological background, we perform a phase-space analysis and identify approximate attractors with late-time acceleration for a wide range of initial conditions. Focusing on two classes of field-space geometry, we derive bounds on parameter space by demanding viable late-time acceleration and the absence of gradient instabilities, as well as from the de Sitter swampland conjecture.Dark energyAttractorInstabilityDe Sitter spaceSwamplandStandard ModelGeodesicPhase spaceQuintessenceField...
- These lectures are a pedagogical introduction to the application of perturbative unitarity to Higgs physics within and beyond the Standard Model (SM). I begin with a review of how perturbative unitarity arises from quantum mechanical scattering theory and apply it to the classic problem of longitudinal vector boson scattering in the SM to derive the famous upper bound on the Higgs boson mass. I then consider extended Higgs sectors, using the two-Higgs-doublet model, the scalar septet model, and the Georgi-Machacek model as case studies. I discuss the resulting Higgs coupling sum rules as well as the intertwined constraints on masses and couplings of the additional Higgs bosons in these models, highlighting the connection between perturbative unitarity and the decoupling limit. I finish with a direct review of the decoupling limit in the two-Higgs-doublet model and a digression on the alignment limit. These notes are based on lectures delivered over the past few years in a graduate-level course on beyond-the-SM phenomenology and are meant as a companion volume to my TASI 2013 lectures on Higgs physics.Higgs bosonUnitarityStandard ModelTwo Higgs Doublet ModelVacuum expectation valueVector bosonHiggs boson massVector boson scatteringGoldstone bosonMixing angle...
- This is a review article for The Review of Particle Physics 2022 (aka the Particle Data Book). It forms a compact review of knowledge of the cosmological parameters near the end of 2021. Topics included are Parametrizing the Universe; Extensions to the standard model; Probes; Bringing observations together; Outlook for the future.Cosmological parametersCosmic microwave backgroundDark matterNeutrinoBaryon acoustic oscillationsDark energyCosmologyNeutrino massSupernova Type IaCosmological model...
- The nature of a neutrino, whether it is a Dirac type or Majorana type, may be comprehensively probed using their quantum statistical properties. If the neutrino is a Majorana fermion, then by definition it is identical and indistinguishable from the corresponding antineutrino. When a Majorana neutrino and antineutrino are pair produced, the corresponding state has to obey the Pauli principle unlike in the Dirac case. We use this property to distinguish between the two cases using the process $B^0 \to \mu^-\,\mu^+\,\nu_\mu\,\bar{\nu}_\mu$. We show that the two cases differ dramatically in a special kinematic scenario where, in the rest frame of the parent $B$ meson, the muons fly away back-to-back (i.e. fly with 3-momenta of equal magnitudes but opposite directions), and so do the neutrino and antineutrino. Unlike any other scenario, we know the energies and magnitudes of $3$-momenta of both the neutrino and the antineutrino in this back-to-back configuration without even directly measuring them. This provides a way of avoiding the constraint imposed by the `practical Dirac-Majorana confusion theorem', as one need not fully integrate over neutrino and antineutrino in this case. As a true signature of the universal principle of quantum statistics which does not depend on the size of the mass of the particle but its spin, the difference between Dirac and Majorana cases in this special kinematic configuration does survive independent of the neutrino mass as long as neutrino mass is nonzero. The analysis presented here is applicable immediately to several other processes with the same final state as in the case of $B^0$ decay without any major change.NeutrinoAntineutrinoMajorana neutrinoMuonNeutrino massForm factorKinematicsFinal stateDecay rateStatistics...
- This lecture provides a brief introduction of thermal field theory within imaginary time vis-a-vis Matsubara formalism. The basic features (such as general two point functions, dispersion behaviours, spectral representation of propagators of fermion and gauge boson) of a material medium in presence of a heat bath have been discussed in details. The tadpole diagram in $\lambda \phi^4$ theory and the self-energy in $\phi^3$ theory have computed and their consequences have also been discussed. The free partition functions for scalar, fermion and gauge field, and interacting scalar field have been obtained from first principle calculation. The leading order(LO), next-to-leading order (NLO) and next-to-next-leading order (NNLO) free energy and pressure for deconfined QCD medium created in heavy-ion collisions have been computed within hard thermal loop perturbation theory (HTLpt). The general features of the deconfined QCD medium have also been outlined with nonperturbative effects.PropagatorPartition functionSelf-energyGauge fieldHard thermal loopQuantum electrodynamicsHard Thermal Loop perturbation theoryGreen's functionScalar fieldGauge fixing...
- Extensions of the Standard Model of particle physics with new Abelian gauge groups allow for kinetic mixing between the new gauge bosons and the hypercharge gauge boson, resulting in mixing with the photon. In many models the mixing with the hypercharge gauge boson captures only part of the kinetic mixing term with the photon, since the new gauge bosons can also mix with the neutral component of the $SU(2)_L$ gauge bosons. We take these contributions into account and present a consistent description of kinetic mixing for general Abelian gauge groups both in the electroweak symmetric and the broken phase. We identify an effective operator that captures the kinetic mixing with $SU(2)_L$ and demonstrate how renormalisable contributions arise if the charged fields only obtain their masses from electroweak symmetry breaking. For the first time, a low-energy theorem for the couplings of novel Abelian gauge bosons with the Standard Model Higgs boson is derived from the one-loop kinetic mixing amplitudes.Kinetic mixingStandard ModelHiggs bosonHyperchargeExtensions of the standard modelStandard Model fermionHiggs boson decayHidden photonBranching ratioElectroweak...
- In this paper we discuss a detection method for the Cosmic Neutrino Background using bremsstrahlung from a neutrino scattering process which has no kinematic threshold, does not rely on a resonance and would in principle allow to measure the velocity distribution of the relic neutrinos. As a concrete example we calculate the rate for solar neutrinos scattering from a relic neutrino emitting a photon. We also provide the energy and angular distributions of the emitted photons.Cosmic neutrino backgroundNeutrinoBremsstrahlungSolar neutrinoNeutrino fluxKinematicsStandard ModelNeutrino magnetic dipole momentDirac neutrinoNeutrino mass...