- Prime number (Prime number)

by Wilson Yu04 Feb 2019 03:47 - Lower and upper (Lower and upper)

by Dr. Wei Wang28 Dec 2018 02:32 - Electrical conductivity (Electrical conductivity)

by Dr. Farhad Daneshvar20 Nov 2018 19:00 - On Measurement Assessment and Division Matrices (On Measurement Assessment and Division Matrices)

by Prof. Hasan Keleş01 Aug 2018 11:58 - Pauli matrices (Pauli matrices)

by Prof. Hasan Keleş16 Feb 2018 07:45 - Fingers of God (Fingers of God)

by Dr. Ganna Ivashchenko18 May 2011 22:42 - Universal Conductance Fluctuations (Universal Conductance Fluctuations)

by Prof. Carlo Beenakker08 Dec 2010 13:33 - Andreev reflection (Andreev reflection)

by Prof. Carlo Beenakker08 Dec 2010 13:33 - Grey-body radiation (Grey-body radiation)

by Prof. Carlo Beenakker08 Jan 2011 20:36 - Quantum point contact (Quantum point contact)

by Prof. Carlo Beenakker08 Jan 2011 20:32

- Despite recent developments, there are a number of conceptual issues on the hadronic light-by-light (HLbL) contribution to the muon $(g-2)$ which remain unresolved. One of the most controversial ones is the precise way in which short-distance constraints get saturated by resonance exchange, particularly in the so-called Melnikov-Vainshtein (MV) limit. In this paper we address this and related issues from a novel perspective, employing a warped five-dimensional model as a tool to generate a consistent realization of QCD in the large$-N_c$ limit. This approach differs from previous ones in that we can work at the level of an effective action, which guarantees that unitarity is preserved and the chiral anomaly is consistently implemented at the hadronic level. We use the model to evaluate the inclusive contribution of Goldstone modes and axial mesons to the HLbL. We find that both anomaly matching and the MV constraint cannot be fulfilled with a finite number of resonances (including the pion) and instead require an infinite number of axial states. Our numbers for the HLbL point at a non-negligible role of the axial mesons, which is closely linked to a correct implementation of QCD short-distance constraints.PionMuonGoldstone bosonEffective actionPseudoscalarInfrared limitAnomaly matching conditionChiral anomalyUnitarityForm factor...
- We present that the $X(3872)$ could be represented as a dynamically generated state in the extended Friedrichs scheme, in which the ratio of "elementariness" and "compositeness" of the different components in the $X(3872)$ is about $Z_{c\bar c}:X_{\bar D^0 D^{0*}}: X_{ D^+ D^{-*}}: X_{\bar D^* D^*}$ $= 1:(2.67\sim 8.85):(0.45\sim 0.46):0.04$. Furthermore, its decays to $\pi^0$ and a $P$-wave charmonium $\chi_{cJ}$ state with $J=0,1$, or $2$, $J/\psi\pi^+\pi^-$, and $J/\psi\pi^+\pi^-\pi^0$ could be calculated out with the help of Barnes-Swanson model. The isospin breaking effects is easily understood in this scheme. This calculation also shows that the decay rate of $X(3872)$ to $\chi_{c1}\pi^0$ is much smaller than its decay rate to $J/\psi\pi^+\pi^-$.X(3872)Decay rateHamiltonianIsospinScattering amplitudeSpin orbitBranching ratioContinuous spectrumHadronic final statesCompleteness relation...
- Two $Z_b$ hadrons with exotic quark structure $\bar bb\bar du$ were discovered by Belle experiment. We present a lattice QCD study of the $\bar bb\bar du$ system in the approximation of static b quarks, where the total spin of heavy quarks is fixed to one. The energies of eigenstates are determined as a function of separation $r$ between $b$ and $\bar b$. The lower eigenstates are related to a bottomonium and a pion. The eigenstate dominated by $B\bar B^*$ has energy significantly below $m_B+m_{B^*}$, which points to sizable attraction for small $r$. The attractive potential $V(r)$ between $B$ and $\bar B^*$ is extracted assuming that this eigenstate is related exclusively to $B\bar B^*$. The Schr\"odinger equation for $B\bar B^*$ within the extracted potential leads to a virtual bound state, whose mass depends on the parametrization of the lattice potential. For certain parametrizations, we find a virtual bound state slightly below $B\bar B^*$ threshold and a narrow peak in the $B\bar B^*$ rate above threshold - these features could be related to $Z_b(10610)$ in experiment. We surprisingly find also a deep bound state within undertaken approximations.Bound stateDegree of freedomHeavy quarkPionLattice QCDTetraquarkLight quarkBelle experimentScattering matrixColor-flavor locking...
- We report on a calculation of form factors for the semileptonic decay of $B$ meson to pion on $2+1$-flavour lattices with lattice spacings from 0.080 fm down to 0.044 fm. Using the M\"obius domain wall fermion action for both sea and valence quarks, we simulate pions with masses down to 225 MeV. By utilizing a range of heavy quark masses up to 2.44 times the mass of the charm quark we extrapolate to the physical $b$ quark mass. We discuss the dependence of the form factors on the pion mass, heavy quark mass, lattice spacing and the momentum-transfer. We extract the CKM matrix element $|V_{ub}|$ through a simultaneous fit with the $B \to \pi\ell\nu$ differential branching fractions provided by the Belle and BaBar collaborations after a chiral-continuum and physical $b$ quark extrapolations of our lattice data.Form factorHeavy quark massesPionDomain wallPion massHeavy quarkCabibbo-Kobayashi-Maskawa matrixLattice QCDHeavy Quark Effective TheoryDecay rate...
- A universal feature of topological insulators is that they cannot be adiabatically connected to an atomic limit, where individual lattice sites are completely decoupled. This property is intimately related to a topological obstruction to constructing a localized Wannier function from Bloch states of an insulator. Here we generalize this characterization of topological phases toward periodically driven systems. We show that nontrivial connectivity of hybrid Wannier centers in momentum space and time can characterize various types of topology in periodically driven systems, which include Floquet topological insulators, anomalous Floquet topological insulators with micromotion-induced boundary states, and gapless Floquet states realized with topological Floquet operators. In particular, nontrivial time dependence of hybrid Wannier centers indicates impossibility of continuous deformation of a driven system into an undriven insulator, and a topological Floquet operator implies an obstruction to constructing a generalized Wannier function which is localized in real and frequency spaces. Our results pave a way to a unified understanding of topological states in periodically driven systems as a topological obstruction in Floquet states.Topological insulatorWilson loopInsulatorsWannier functionBerry phaseTime-reversal symmetryWinding numberTopological invariantHamiltonianTopological order...
- The construction of gravitational Wilson lines in the Chern-Simons formulation of $AdS_3$ gravity in terms of composite operators in the dual boundary conformal field theory is reviewed. New evidence is presented that the Wilson line, dimensionally regularized and suitably renormalized, behaves as a bi-local operator of two conformal primaries whose dimension is predicted by SL(2,R) current algebra.Wilson loopRenormalizationOperator product expansionConformal field theoryGauge fieldAnti de Sitter spaceRegularizationChern-Simons termPrimary fieldGauge transformation...
- It was recently shown by Harlow that any quantum error correcting code, satisfying the same complementary recovery properties as AdS/CFT, will obey a version of the Ryu-Takayanagi formula. In his most general result, Harlow allowed the bulk algebras to have nontrivial center, which was necessary for the "area operator" in this Ryu-Takayanagi formula to be nontrivial. However, the boundary Hilbert space was still assumed to factorise into Hilbert spaces associated with complementary boundary regions. We extend this work to include more general boundary theories, such as gauge theories, where the subalgebras associated with boundary regions may also have nontrivial center. We show the equivalence of a set of four conditions for a bulk algebra to be reconstructable from a boundary algebra, and then show that complementary recovery implies that the algebraic boundary entropy obeys a Ryu-Takayanagi formula. In contrast, we show that the distillable boundary entropy does not obey any such formula. If an additional "log dim R" term is added to the algebraic entropy, it will still obey a Ryu-Takayanagi formula, with a different area operator. However, since the "log dim R" term is a sum over local boundary contributions, we argue that it can only be related to the regularisation of the area at the bulk cut-off.EntropyConformal field theoryAdS/CFT correspondenceVon Neumann algebraEntanglementCommutantQuantum error correctionSuperselectionEntanglement entropyVon neumann entropy...
- High-temperature superconductivity in Fe-based pnictides and chalcogenides has been one of the most significant recent discoveries in condensed matter physics and has attracted remarkable attention in the last decade. These materials are characterized by a complex fermiology and, as a result, feature a wide range of electronic properties as a function of different tuning parameters such as chemical doping, temperature and pressure. Along the path towards the comprehension of the physical mechanisms underlying this rich phenomenology, NMR (nuclear magnetic resonance) and NQR (nuclear quadrupole resonance) have played a role of capital importance that we review in this work. In particular, we address how NMR has contributed to the current understanding of the main regions of the electronic phase diagram of Fe-based pnictides, that is, the -- sometimes coexisting -- antiferromagnetic spin-density wave and superconducting states. We evidence the unique capability of NMR as local-probe technique of investigating the effect of quenched disorder and chemical impurities. Then, we review the NMR signatures of low-frequency fluctuations associated with the development of electronic nematicity as well as with the motion of superconducting flux lines. Finally, we discuss recent contributions of NMR and NQR which evidence an intrinsically inhomogeneous electronic charge distribution as well as an orbitally-selective behaviour.DopingNuclear magnetic resonanceIron based superconductorsSuperconductivityParamagneticSuperconductorSpin density wavePhase diagramFermi surfaceAntiferromagnetic...
- The extraction of brain functioning features is a crucial step in the definition of brain-computer interfaces (BCIs). In the last decade, functional connectivity (FC) estimators have been increasingly explored based on their ability to capture synchronization between multivariate brain signals. However, the underlying neurophysiological mechanisms and the extent to which they can improve performance in BCI-related tasks, is still poorly understood. To address this gap in knowledge, we considered a group of 20 healthy subjects during an EEG-based hand motor imagery (MI) task. We studied two well-established FC estimators, i.e. spectral- and imaginary-coherence, and investigated how they were modulated by the MI task. We characterized the resulting FC networks by extracting the strength of connectivity of each EEG sensor and compared the discriminant power with respect to standard power spectrum features. At the group level, results showed that while spectral-coherence based network features were increasing the controlateral motor area, those based on imaginary-coherence were decreasing. We demonstrated that this opposite, but complementary, behavior was respectively determined by the increase in amplitude and phase synchronization between the brain signals. At the individual level, we proved that including these network connectivity features in the classification of MI mental states led to an overall improvement in accuracy. Taken together, our results provide fresh insights into the oscillatory mechanisms subserving brain network changes during MI and offer new perspectives to improve BCI performance.Statistical estimatorClassificationPhase synchronizationFunctional connectivityLinear discriminant analysisFeature extractionDisorderPower spectral densityTime SeriesDiscrete Fourier transform...
- We measure the rest-frame UV luminosity function (LF) at $z \sim 4$ self-consistently over a wide range in absolute magnitude ($-27 \lesssim M_{\rm UV} \lesssim -20$). The LF is measured with 46,904 sources selected using a photometric redshift approach over $ \sim 6$ deg$^2$ of the combined COSMOS and XMM-LSS fields. We simultaneously fit for both AGN and galaxy LFs using a combination of Schechter or Double Power Law (DPL) functions alongside a single power law for the faint-end slope of the AGN LF. We find a lack of evolution in the shape of the bright-end of the LBG component when compared to other studies at $z \simeq 5$ and evolutionary recipes for the UV LF. Regardless of whether the LBG LF is fit with a Schechter function or DPL, AGN are found to dominate at $M_{\rm UV} < -23.5$. We measure a steep faint-end slope of the AGN LF with $\alpha_{AGN} = -2.09^{+0.35}_{-0.38}$ ($-1.66^{+0.29}_{-0.58}$) when fit alongside a Schechter function (DPL) for the galaxies. Our results suggest that if AGN are morphologically selected it results in a bias to lower number densities. Only by considering the full galaxy population over the transition region from AGN to LBG domination can an accurate measurement of the total LF be attained.Luminosity functionActive Galactic NucleiLyman break galaxyGalaxyMilky WayPhotometric redshiftCompletenessLuminositySchechter functionSpectral energy distribution...
- Query-based open-domain NLP tasks require information synthesis from long and diverse web results. Current approaches extractively select portions of web text as input to Sequence-to-Sequence models using methods such as TF-IDF ranking. We propose constructing a local graph structured knowledge base for each query, which compresses the web search information and reduces redundancy. We show that by linearizing the graph into a structured input sequence, models can encode the graph representations within a standard Sequence-to-Sequence setting. For two generative tasks with very long text input, long-form question answering and multi-document summarization, feeding graph representations as input can achieve better performance than using retrieved text portions.GraphAttentionKnowledge graphEmbeddingKnowledge baseArchitectureGenetically modified organismComputational linguisticsRankingRank...
- This is a brief pedagogic introduction to searches for new physics with top quarks. It covers indirect searches for heavy new particles based on standard model effective theory and direct searches for new signatures of a light hidden sector. LHC and flavor observables complement and strengthen each other in this endeavor.Top quarkHiggs bosonLarge Hadron ColliderStandard ModelPair productionBELLE IIHidden sectorEffective theoryWilson coefficientsChirality...
- The lepton flavor universality violating (LFUV) measurements $R_K$ and $R_{K^*}$ in $B$ meson decays can be accounted for in non-universal $Z'$ models. We constrain the couplings of these $Z'$ models by performing a global fit to correlated $b \to s \ell \ell$ and $b \to d \ell \ell $ processes, and calculate their possible implications for $B_s \to \bar{K}^*\ell \ell$ observables. For real new physics (NP) couplings, the 1-$\sigma$ favored parameters allow the corresponding LFUV ratio $R_{K^*}^{(s)}$ in $B_s \to \bar{K}^*\ell \ell$ to range between 0.8 -- 1.2 at low $q^2$. Complex NP couplings improve the best fit only marginally, however they allow a significant enhancement of the branching ratio, while increasing the range of $R_{K^*}^{(s)}$ at low $q^2$ to 0.8 -- 1.8. We find that NP could cause zero-crossing in the forward-backward asymmetry $A_{FB}$ to shift towards lower $q^2$ values, and enhancement in the magnitude of integrated $A_{FB}$. The $CP$ asymmetry $A_{CP}$ may be suppressed and even change sign. The simultaneous measurements of integrated $R_{K^*}^{(s)}$ and $A_{CP}$ values to 0.1 and 1% respectively, would help in constraining the effective NP Wilson coefficient $C_9$ in $ b \to d \mu \mu$ interactions.Standard ModelBranching ratioWilson coefficientsForm factorNeutrino trident productionMuonForward-backward asymmetryLHCb experimentMeson decaysFlavour Changing Neutral Currents...
- We investigate the quantum numbers of the pentaquark states $\textrm{P}_{\textrm{c}}^{+}$, which are composed of four (three flavors) quarks and an antiquark, by analyzing their inherent nodal structure in this paper. Assuming that the four quarks form a tetrahedron or a square, and the antiquark locates at the center of the four quark cluster, we determine the nodeless structure of the states with orbital angular moment $L \leq 3$, and in turn, the accessible low-lying states. Since the inherent nodal structure depends only on the inherent geometric symmetry, we propose the quantum numbers $J^{P}$ of the low-lying pentaquark states $\textrm{P}_{c}^{+}$ may be ${\frac{3}{2}}^{-}$, ${\frac{5}{2}}^{-} $, ${\frac{3}{2}}^{+}$, ${\frac{5}{2}}^{+} $, independent of dynamical models.PentaquarkOrbital angular momentum of lightPermutationColor-flavor lockingMolecular structureFew-body systemsHeavy quarkBound stateAttentionExcited state...
- We study the expected sensitivity at Belle and Belle II for four-body $\tau^\mp \to X^\pm l^\mp l^\mp \nu_{\tau}$ decays where $l=e$ or $\mu$ and $X=\pi$, $K$, $\rho$ and $K^*$ mesons. These decay processes violate the total lepton number ($|\Delta L|=2$ ) and they can be induced by the exchange of Majorana neutrinos. In particular, we consider lifetimes in the accessible ranges of $\tau_N$ = 5, 100 ps and extract the limits on $|V_{\ell N}|^2$ without any additional assumption on the relative size of the mixing matrix elements. For an integrated luminosity collected of 1 ab$^{-1}$ at Belle, we found significant sensitivity on branching fractions of the order BR($\tau^\mp \to X^\pm l^\mp l^\mp \nu_{\tau}$) $\sim 10^{-8}$. For an integrated luminosity expected of 50 ab$^{-1}$ and intermediate luminosity of 10 ab$^{-1}$ at the Belle II, we found significant sensitivity on branching fractions of the order BR($\tau^\mp \to X^\pm l^\mp l^\mp \nu_{\tau}$) $\sim 10^{-9}-10^{-8}$. We use these sensitivities to set limits for the exclusion regions on the parameter space $(m_N, |V_{\ell N}|^2)$ associated with the heavy neutrino; such that for a $|V_{\ell N}|^2 \sim \mathcal{O}(10^{-5})$ at $\tau_N = 100$ ps, we find the bounds as $0.140 < m_N < 1.776$ GeV for $\tau^- \to X^+ e^- e^- \nu_\tau$ and $0.245 < m_N < 1.671 $ GeV for $\tau^- \to X^+ \mu^- \mu^- \nu_\tau$.BELLE IIBranching ratioSterile neutrinoIntegrated luminosityDecay widthMajorana neutrinoLepton number violationTau leptonStandard ModelLuminosity...
- Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions, and allow searches for physics beyond the Standard Model. We present the first results on isospin amplitudes in $b$-baryon decays, using data corresponding to an integrated luminosity of 8.5 fb$^{-1}$, collected with the LHCb detector in $pp$ collisions at center of mass energies of 7, 8 and 13 TeV. The isospin amplitude ratio $|A_1(\Lambda_b^0\to J/\psi \Sigma^0)/A_0(\Lambda_b^0\to J/\psi\Lambda)|$, where the subscript on $A$ indicates the final-state isospin, is measured to be less than $1/20.9$ at 95\% confidence level. The Cabibbo suppressed $\Xi_b^0\to J/\psi\Lambda$ decay is observed for the first time, allowing for the measurement $|A_0(\Xi_b^0\to J/\psi\Lambda)/A_{1/2}(\Xi_b^0\to J/\psi\Xi^0)| =0.44 \pm 0.06\pm 0.02$, where the uncertainties are statistical and systematic, respectively.IsospinLHCb experimentMass distributionBranching ratioBaryon decaysIntegrated luminosityMass spectrumPionMuonSystematic error...
- We comment on the results of the recent search by the LHCb collaboration for the doubly charmed baryon $\Xi_{cc}^+$.LHCb experimentCharmed baryonsLook elsewhere effectIsospinTetraquarkIsospin symmetryGlobal significanceLocal significanceSystematic errorDiquark...
- Invited "News & Views" for the journal, SCIENCE CHINA: Physics, Mechanics & Astronomy, on a recently new search for the doubly charmed baryon $\Xi_{cc}^+$ at the LHC, which is done by the LHCb Collaboration, arXiv:1909.12273.Large Hadron ColliderCharmed baryonsLHCb experimentColliderData samplingDecay channelsBranching ratioIntegrated luminosityProduction cross-sectionDiquark...
- Doped SrTiO$_3$, one of the most dilute bulk systems to display superconductivity, is perhaps the first example of an unconventional superconductor, as it does not fit into the standard BCS paradigm. More than five decades of research has revealed a rich temperature-carrier concentration phase diagram that showcases a superconducting dome, proximity to a putative quantum critical point, Lifshitz transitions, a multi-gap pairing state and unusual normal-state transport properties. Research has also extended beyond bulk SrTiO$_3$, ushering the new field of SrTiO$_3$-based heterostructures. Because many of these themes are also featured in other quantum materials of contemporary interest, recent years have seen renewed interest in SrTiO$_3$. Here, we review the challenges and recent progress in elucidating the superconducting state of this model system. At the same time that its extreme dilution requires to revisit several of the approximations that constitute the successful Migdal-Eliashberg description of electron-phonon superconductivity, including the suppression of the Coulomb repulsion via the Tolmachev-Anderson-Morel mechanism, it opens interesting routes for alternative pairing mechanisms whose applicability remains under debate. For instance, pairing mechanisms involving longitudinal optical phonons have to overcome the hurdles created by the anti-adiabatic nature of the pairing interaction, whereas mechanisms that rely on the soft transverse optical phonons associated with incipient ferroelectricity face challenges related to the nature of the electron-phonon coupling. Proposals in which pairing is mediated by plasmons or promoted locally by defects are also discussed. We finish by surveying the existing evidence for multi-band superconductivity and outlining promising directions that can potentially shed new light on the rich problem of superconductivity in SrTiO$_3$.SuperconductivityPhononDopingQuantum critical pointSuperconductorFermi energyPlasmonTransverse optical modeBardeen Cooper SchriefferDomes...
- According to the bulk-edge correspondence principle, the physics of the gapless edge in the quantum Hall effect determines topological order in the gapped bulk. As the bulk is less accessible, the last two decades saw the emergence of several experimental techniques that invoke the study of the compressible edge. We review the properties of the edge, and describe several experimental techniques that include shot noise and thermal noise measurements, interferometry, and energy (thermal) transport at the edge. We pay special attention to the filling factor 5/2 in the first excited Landau level (in two-dimensional electron gas in GaAs), where experimental evidence of a non-abelian topological order was found. A brief discussion is devoted to recent interferometry experiments that uncovered unexpected physics in the integer quantum Hall effect. The chapter also addresses the theory of edge states, for systems with abelian and non-abelian topological orders.Topological orderExperimental techniqueInterferometryAttentionFilling factor 5/2Edge excitationsShot noiseLandau levelCorrespondence principleQuantum Hall Effect...
- We use the open quantum system formalism to study the dynamical in-medium evolution of quarkonium. The system of quarkonium is described by potential non-relativistic QCD while the environment is a weakly coupled quark-gluon plasma in local thermal equilibrium below the melting temperature of the quarkonium. Under the Markovian approximation, it is shown that the Lindblad equation leads to a Boltzmann transport equation if a Wigner transform is applied to the system density matrix. Our derivation illuminates how the microscopic time-reversibility of QCD is consistent with the time-irreversible in-medium evolution of quarkonium states. Static screening, dissociation and recombination of quarkonium are treated in the same theoretical framework. In addition, quarkonium annihilation is included in a similar way, although the effect is negligible for the phenomenology of the current heavy ion collision experiments. The methods used here can be extended to study quarkonium dynamical evolution inside a strongly coupled QGP, a hot medium out of equilibrium or cold nuclear matter, which is important to studying quarkonium production in heavy ion, proton-ion, and electron-ion collisions.QuarkoniumHeavy quarkQuark-gluon plasmaBoltzmann transport equationBound stateDensity matrixWigner transformRecombinationTransport equationHamiltonian...
- We consider the ferromagnetic quantum Heisenberg model in one dimension, for any spin $S\geq 1/2$. We give upper and lower bounds on the free energy, proving that at low temperature it is asymptotically equal to the one of an ideal Bose gas of magnons, as predicted by the spin-wave approximation. The trial state used in the upper bound yields an analogous estimate also in the case of two spatial dimensions, which is believed to be sharp at low temperature.HamiltonianSpin waveHeisenberg modelHeisenberg spin chainSpin wave theoryNearest-neighbor siteMagnonVariational principleCreation and annihilation operatorsBose gas...
- Training generative adversarial networks requires balancing of delicate adversarial dynamics. Even with careful tuning, training may diverge or end up in a bad equilibrium with dropped modes. In this work, we introduce a new form of latent optimisation inspired by the CS-GAN and show that it improves adversarial dynamics by enhancing interactions between the discriminator and the generator. We develop supporting theoretical analysis from the perspectives of differentiable games and stochastic approximation. Our experiments demonstrate that latent optimisation can significantly improve GAN training, obtaining state-of-the-art performance for the ImageNet (128 x 128) dataset. Our model achieves an Inception Score (IS) of 148 and an Fr\'echet Inception Distance (FID) of 3.4, an improvement of 17% and 32% in IS and FID respectively, compared with the baseline BigGAN-deep model with the same architecture and number of parameters.Generative Adversarial NetArchitectureStochastic approximationOptimizationPositive semi definiteFisher information matrixUniform distributionLikelihood functionAblationRegularization...
- Neural networks have a reputation for being better at solving statistical or approximate problems than at performing calculations or working with symbolic data. In this paper, we show that they can be surprisingly good at more elaborated tasks in mathematics, such as symbolic integration and solving differential equations. We propose a syntax for representing mathematical problems, and methods for generating large datasets that can be used to train sequence-to-sequence models. We achieve results that outperform commercial Computer Algebra Systems such as Matlab or Mathematica.Binary treeWolfram MathematicaTraining setNeural networkComputer algebra systemDeep learningArithmeticBinary caseMachine translationOrdinary differential equations...
- In this work we study the weak decays of $\Xi_{cc}\to\Xi_c$ and $\Xi_{cc}\to\Xi'_c$ in the light-front quark model. Generally, a naive, but reasonable conjecture suggests that the $cc$ subsystem in $\Xi_{cc}$ ( $us$ pair in $\Xi^{(')}_c$) stands as a diquark with definite spin and color assignments. During the concerned processes, the diquark of the initial state is not a spectator, and must be broken. A Racah transformation would decompose the original $(cc)q$ into a combination of $c(cq)$ components. Thus we may deal with the decaying $c$ quark alone while keeping the $(cq)$ subsystem as a spectator. With the re-arrangement of the inner structure we calculate the form factors numerically and then obtain the rates of semi-leptonic decays and non-leptonic decays, which will be measured in the future.DiquarkForm factorLight frontWeak decayDecay rateCharmed baryonsLight quarkHelicityDecay widthCharm quark...
- Observations of the early Universe suggest that reionization was complete by $z\sim6$, however, the exact history of this process is still unknown. One method for measuring the evolution of the neutral fraction throughout this epoch is via observing the Ly$\alpha$ damping wings of high-redshift quasars. In order to constrain the neutral fraction from quasar observations, one needs an accurate model of the quasar spectrum around Ly$\alpha$, after the spectrum has been processed by its host galaxy but before it is altered by absorption and damping in the intervening IGM. In this paper, we present a novel machine learning approach, using artificial neural networks, to reconstruct quasar continua around Ly$\alpha$. Our QSANNdRA algorithm improves the error in this reconstruction compared to the state-of-the-art PCA-based model in the literature by 14.2% on average, and provides an improvement of 6.1% on average when compared to an extension thereof. In comparison with the extended PCA model, QSANNdRA further achieves an improvement of 22.1% and 16.8% when evaluated on low-redshift quasars most similar to the two high-redshift quasars under consideration, ULAS J1120+0641 at $z=7.0851$ and ULAS J1342+0928 at $z=7.5413$, respectively. Using our more accurate reconstructions of these two $z>7$ quasars, we estimate the neutral fraction of the IGM using a homogeneous reionization model and find $\bar{x}_\mathrm{HI} = 0.25^{+0.05}_{-0.05}$ at $z=7.0851$ and $\bar{x}_\mathrm{HI} = 0.60^{+0.11}_{-0.11}$ at $z=7.5413$. Our results are consistent with the literature and favour a rapid end to reionization.QuasarSloan Digital Sky SurveyPrincipal component analysisTraining setHigh-redshift quasarIntergalactic mediumDamping Wing of Gunn-Peterson TroughReionizationNeural networkSignal to noise ratio...
- We investigate if, for a fixed number density of targets and redshift, there is an optimal way to select a galaxy sample in order to measure the baryon acoustic oscillation (BAO) scale, which is used as a standard ruler to constrain the cosmic expansion. Using the mock galaxy catalogue built by Smith et al. in the Millennium-XXL N-body simulation with a technique to assign galaxies to dark matter haloes based on halo occupation distribution modelling, we consider the clustering of galaxies selected by luminosity, colour and local density. We assess how well the BAO scale can be extracted by fitting a template to the power spectrum measured for each sample. We find that the BAO peak position is recovered equally well for samples defined by luminosity or colour, while there is a bias in the BAO scale recovered for samples defined by density. The BAO position is contracted to smaller scales for the densest galaxy quartile and expanded to large scales for the two least dense galaxy quartiles. For fixed galaxy number density, density-selected samples have higher uncertainties in the recovered BAO scale than luminosity- or colour-selected samples.GalaxyBaryon acoustic oscillationsMatter power spectrumLuminosityHalo Occupation DistributionMilky WayVirial massRankSatellite galaxyTwo-point correlation function...
- We carry out a detailed strong lensing analysis of a sub-sample of eight galaxy clusters of the CLASH survey, in the redshift range of $ z_{\rm cluster} = [0.23-0.59]$, using extensive spectroscopic information, primarily MUSE archival data complemented with CLASH-VLT redshift measurements. Different models are tested in each cluster depending on the complexity of its mass distribution and on the number of detected multiple images. Four clusters show more than five spectroscopically confirmed multiple image families. In this sample, we do not make use of families that are only photometrically identified, in order to reduce model degeneracies and systematics due to the potential misidentifications of some multiple images. We present spectroscopic confirmation of 27 multiply lensed sources, with no previous spectroscopic measurements, spanning over the redshift range of $z_{\rm src}=[0.7-6.1]$. Moreover, we confirm an average of $48$ galaxy members in the core of each cluster, thanks to the high efficiency and large field of view of MUSE. Despite having different properties (i.e., number of mass components, total mass, redshift, etc), the projected total mass and mass density profiles of all clusters have very similar shapes, when rescaled by independent measurements of $M_{200c}$ and $R_{200c}$. Specifically, we measure the mean value of the projected total mass of our cluster sample within 10 (20)% of $R_{200c}$ to be 0.13 (0.32) of $M_{200c}$, with a remarkably small scatter of 5 (6)%. Furthermore, the large number of high-z sources and the precise magnification maps derived in this work for four clusters add up to the sample of high-quality gravitational telescopes to be used to study the faint and distant Universe. The strong lensing models and the full redshift catalogues from MUSE are publicly available.MAssive Cluster SurveyMulti Unit Spectroscopic ExplorerStrong gravitational lensingCluster Lensing And Supernova survey with HubbleMass distributionGalaxyField of viewHubble Space TelescopeVLT telescopeBrightest cluster galaxy...
- We study the fractional Laplacian and the homogeneous Sobolev spaces on R^d , by considering two definitions that are both considered classical. We compare these different definitions, and show how they are related by providing an explicit correspondence between these two spaces, and show that they admit the same representation. Along the way we also prove some properties of the fractional Laplacian.Sobolev spaceFractional LaplacianCauchy sequenceHardy spaceIsomorphismNonnegativeLocally integrable functionEmbeddingDilationRiesz transform...
- We perform a phenomenological analysis of the observable consequences on the extended scalar sector of the SMASH (Standard Model - Axion - Seesaw - Higgs portal inflation) framework. We solve the vacuum metastability problem in a suitable region of SMASH scalar parameter spaces and discuss the one-loop correction to triple Higgs coupling $\lambda_{HHH}$. We also find that the correct neutrino masses and mass squared differences and baryonic asymmetry of the universe can arise from this model and consider running of the Yukawa couplings of the model. In fact, we perform a full two-loop renormalization group analysis of the SMASH model.Standard ModelHiggs bosonNeutrino massNeutrinoHiggs stability boundRenormalisation group equationsYukawa couplingPlanck scaleHigh-luminosity LHCLarge Hadron Collider...
- Hilbert's program of establishing consistency of theories like Peano arithmetic PA using only finitary tools has long been considered impossible. The standard reference here is Goedel's Second Incompleteness Theorem by which a theory T, if consistent, cannot prove the arithmetical formula ConT, 'for all x, x is not a code of a proof of a contradiction in T.' We argue that such arithmetization of consistency distorts the problem. ConT is stronger than the original notion of consistency, hence Goedel's theorem does not yield impossibility of proving consistency by finitary tools. We consider consistency in its standard form 'no sequence of formulas S is a derivation of a contradiction.' Using partial truth definitions, for each derivation S in PA we construct a finitary proof that S does not contain 0=1. This establishes consistency for PA by finitary means and vindicates, to some extent, Hilbert's consistency program. This also suggests that in the arithmetical form, consistency, similar to induction, reflection, truth, should be represented by a scheme rather than by a single formula.FinitaryArithmeticMathematical proofCompletenessHilbert's programStandard ModelLöb's theoremProof theoryMathematical inductionGödel's incompleteness theorems...
- Using a general parameterization of two-body scattering amplitude, we systematically analyze the corresponding data on $X(3872)$, more explicitly, the CDF data on inclusive $p\bar{p}$ scattering to $J/\psi \pi^+\pi^-$, and the Belle and BaBar data on $B$ decays to $K\, J/\psi \pi^+\pi^-$ and $K D\bar{D}^{*0}$ around the $D^0\bar{D}^{*0}$ threshold. We achieve a good reproduction of data and find that the $X(3872)$ can be interpreted as a bound and/or virtual state, or even higher-order (double or triple) virtual sate pole. The latter point was not realized previously in the literature. % The latter point has not been realized in other literatures. As a result, the compositeness of the $X(3872)$ can vary largely from nearly 0 to 1. More higher-precision data is needed to discriminate its pole structure and nature.X(3872)CDD poleScattering amplitudeBound stateScattering lengthFinal state interactionsExotic hadronSelf-energyRadius of convergenceResonance...
- At present, there are many experimental and theoretical results for $J/\psi\rightarrow\eta_{c}+\gamma$ process, while the results are inconsistent based on different methods and considerations. In this paper, the light cone sum rule method is used in studying the radiative decay $J/\psi\rightarrow\eta_{c}+\gamma$. We give the transition form factor of this process based on the leading twist distribution amplitude of $\eta_{c}$ meson, with this form factor further obtain the decay width. Our result is compatible with recent experimental date within errors, and it is consistent with the results of previous sum rule method. A comparison of our result with others' about the decay width is also presented.Light-cone sum rulesDecay widthForm factorRadiative decayTransition form factorDualityOperator product expansionExcited stateEffective field theoryBorel parameter...
- We use the variational principle approach to derive the large $N$ holographic dictionary for two-dimensional $T\bar T$-deformed CFTs, for both signs of the deformation parameter. The resulting dual gravitational theory has mixed boundary conditions for the non-dynamical graviton; the boundary conditions for matter fields are undeformed. When the matter fields are turned off and the deformation parameter is negative, the mixed boundary conditions for the metric at infinity can be reinterpreted on-shell as Dirichlet boundary conditions at finite bulk radius, in agreement with a previous proposal by McGough, Mezei and Verlinde. The holographic stress tensor of the deformed CFT is fixed by the variational principle, and in pure gravity it coincides with the Brown-York stress tensor on the radial bulk slice with a particular cosmological constant counterterm contribution. In presence of matter fields, the connection between the mixed boundary conditions and the radial "bulk cutoff" is lost. Only the former correctly reproduce the energy of the bulk configuration, as expected from the fact that a universal formula for the deformed energy can only depend on the universal asymptotics of the bulk solution, rather than the details of its interior. The asymptotic symmetry group associated with the mixed boundary conditions consists of two commuting copies of a state-dependent Virasoro algebra, with the same central extension as in the original CFT.Conformal field theoryExpectation ValueMixed boundary conditionDiffeomorphismBlack holeHorizonDirichlet boundary conditionAnti de Sitter spaceVariational principleDs meson...
- I will review simplified models with leptoquarks, which can explain recent anomalies in $B$-meson physics, and I will indicate the High-Luminosity LHC prospects for testing these theories, with a special focus to the efficient channel of pair leptoquark production in the $t\bar t$ plus missing energy final state.LeptoquarkHigh-luminosity LHCB mesonMissing energyTheoryMesons...
- We study the impact of contact interactions involving two leptons (electrons or muons) and two $b$-quarks ($b \bar{b} \ell^+ \ell^-$) on the high-mass di-lepton region at the LHC. We consider different selections of $b$-tagged jet multiplicities in the di-lepton final states: inclusive (no selection), 0, 1 and 2 $b$-tagged jets, and show that the single $b$-jet selection significantly improves the sensitivity to New Physics (NP) in the form of the $b \bar{b} \ell^+ \ell^-$ contact term. We obtain a better sensitivity compared to the currently existing searches of NP in the di-lepton inclusive channel. In particular, the expected limits go beyond competitive bounds set by LEP (for electrons) on the scale of new physics, $\Lambda$, by a factor of $1.4-3.9$, depending on the chirality structure of the operator. In addition, the expected limits on $\Lambda$, set by using a non-resonant LHC di-lepton inclusive search, are expected to be improved by a factor of $1.3-1.4$ for both electrons and muons.MuonLarge Hadron ColliderStandard ModelChiralityInterferenceHigh massPartonScale of new physicsBounded setATLAS Experiment at CERN...
- The interstellar neutral (ISN) gas enters the heliosphere and is detected at few au from the Sun, as demonstrated by Ulysses and the Interstellar Boundary Explorer (IBEX) missions. Ulysses observed ISN gas from different vantage points in a polar orbit from 1994 to 2007, while IBEX has been observing in an Earth's orbit in a fixed direction relative to the Sun from 2009. McComas et al. 2018 reported about an IMAP-Lo detector onboard the Interstellar Mapping and Acceleration Probe (IMAP), with an ability to track the ISN flux in the sky. We present observation geometries for ISN gas for a detector with the capability to adjust the boresight direction along the Earth orbit over a year within a multi-choice ISN observation scheme. We study science opportunities from the observations as a function of time during a year and the phase of solar activity. We identify observation geometries and determine the observation seasons separately for various ISN species and populations. We find that using an adjustable viewing direction allows for ISN gas observations in the upwind hemisphere, where the signal is not distorted by gravitational focusing, in addition to the viewing of ISN species throughout the entire year. Moreover, we demonstrate that with appropriately adjusted observation geometries, primary and secondary populations can be fully separated. Additionally, we show that atoms of ISN gas on indirect trajectories are accessible for detection and we present their impact on the study of the ionization rates for ISN species.IonizationSunSolar maximumSolar minimumHeliosphereEarth orbitUlyssesStatisticsSolar activitySolar cycle...
- The claimed detection of large amounts of substructure in lensing flux anomalies, and in Milky Way stellar stream gaps statistics, has lead to a step change in constraints on simple warm dark matter models. In this study we compute predictions for the halo mass function both for these simple models and also for comprehensive particle physics models of sterile neutrinos and dark acoustic oscillations. We show that the mass function fit of Lovell et al. underestimates the number of haloes less massive than the half-mode mass, $M_\mathrm{hm}$, by a factor of 2, relative to the extended Press-Schechter (EPS) method. The alternative approach of applying EPS to the Viel et al. matter power spectrum fit instead suggests good agreement at $M_\mathrm{hm}$ relative to the comprehensive model matter power spectra results, although the number of haloes with mass $<M_\mathrm{hm}$ is still suppressed due to the absence of small scale power in the fitting function. Overall, we find that the number of dark matter haloes with masses $<10^{8}M_\mathrm{sun}$ predicted by competitive particle physics models is underestimated by a factor of $\sim2$ when applying popular fitting functions, although careful studies that follow the stripping and destruction of subhaloes will be required in order to draw robust conclusions.Extended Press-Schechter formalismMass functionETHOSDark matter subhaloHalo mass functionWarm dark matterCold dark matterMatter power spectrumDark matter modelMilky Way...
- We investigate the generation of seed magnetic field through the Chern-Simons coupling between the U(1) gauge field and an axion field that commences to oscillate at various epoch, depending on the mass scale. We address axions which begin oscillation during inflation, reheating, and also the radiation dominated era after the thermalization of the Universe. We study the resonant generation mechanisms and highlight that a small oscillation time scale with respect to that of the cosmic expansion can lead to an efficient generation of (hyper) magnetic field via resonant generation, even for ${\cal O}(1)$ coupling. In addition, we demonstrate that the generated field can be helical due to the tachyonic amplification phase prior to the onset of oscillation. Furthermore, it is shown that the parametric resonance during reheating can generate a circularly polarized (hyper) magnetic field in a void region with the present amplitude $B_0 =3\times 10^{-15}$Gauss and the coherent length $\lambda_0 = 0.3$pc without being plagued by the backreaction issue.AxionGauge fieldInflationReheatingHelicityInflatonExpansion of the UniverseInstabilityCosmological magnetic fieldChern-Simons term...
- We model the 21-cm signal and LAE population evolution during the epoch of reionization in order to predict the 21cm-LAE cross-power spectrum. We employ high-dynamic-range simulations of the IGM to create models that are consistent with constraints from the CMB, Lyman-$\alpha$ forest and LAE population statistics. Using these models we consider the evolution of the cross-power spectrum for a selection of realistic reionization histories and predict the sensitivity of current and upcoming surveys to measuring this signal. We find that the imprint of a delayed-end to reionization can be observed by future surveys, and that strong constraints can be placed on the progression of reionization as late as $z=5.7$ using a Subaru-SKA survey. We make predictions for the signal-to-noise ratios achievable by combinations of Subaru/PFS with the MWA, LOFAR, HERA and SKA interferometers. We find that a Subaru-SKA survey could measure the cross-power spectrum for a late reionization at $z=6.6$ with a total signal-to-noise greater than 5, making it possible to constrain both the timing and bubble size at the end of reionization. Furthermore, we find that expanding the current Subaru/PFS survey area and depth by a factor of three would double the total signal-to-noise.Lyman alpha emitterReionizationHydrogen 21 cm lineHistory of the reionizationSquare Kilometre ArraySubaru telescopeIntergalactic mediumCross-correlationSignal to noise ratioEpoch of reionization...
- According to Harlow and Hayden [arXiv:1301.4504] the task of distilling information out of Hawking radiation appears to be computationally hard despite the fact that the quantum state of the black hole and its radiation is relatively un-complex. We trace this computational difficulty to a geometric obstruction in the Einstein-Rosen bridge connecting the black hole and its radiation. Inspired by tensor network models, we conjecture a precise formula relating the computational hardness of distilling information to geometric properties of the wormhole - specifically to the exponential of the difference in generalized entropies between the two non-minimal quantum extremal surfaces that constitute the obstruction. Due to its shape, we call this obstruction the "Python's Lunch", in analogy to the reptile's postprandial bulge.Black holeEntropyPythonQubitHawking radiationWormholeHorizonEntanglementIsometryMinimax...
- In this paper, we give a resolution of the generalized Fermat equations $$x^5 + y^5 = 3 z^n \text{ and } x^{13} + y^{13} = 3 z^n,$$ for all integers $n \ge 2$, and all integers $n \ge 2$ which are not a multiple of $7$, respectively, using the modular method with Frey elliptic curves over totally real fields. The results require a refined application of the multi-Frey technique, which we show to be effective in new ways to reduce the bounds on the exponents $n$. We also give a number of results for the equations $x^5 + y^5 = d z^n$, where $d = 1, 2$, under additional local conditions on the solutions. This includes a result which is reminiscent of the second case of Fermat's Last Theorem, and which uses a new application of level raising at $p$ modulo $p$.Elliptic curveTorsion tensorCoprimeModularityClassificationModular formFermat's Last TheoremSubgroupPrime numberIsomorphism...
- Central in entanglement theory is the characterization of local transformations among pure multipartite states. As a first step towards such a characterization, one needs to identify those states which can be transformed into each other via local operations with a non-vanishing probability. The classes obtained in this way are called SLOCC classes. They can be categorized into three disjoint types: the null-cone, the polystable states and strictly semistable states. Whereas the former two are well characterized, not much is known about strictly semistable states. We derive a criterion for the existence of the latter. In particular, we show that there exists a strictly semistable state if and only if there exist two polystable states whose orbits have different dimensions. We illustrate the usefulness of this criterion by applying it to tripartite states where one of the systems is a qubit. Moreover, we scrutinize all SLOCC classes of these systems and derive a complete characterization of the corresponding orbit types. We present representatives of strictly semistable classes and show to which polystable state they converge to via local regular operators.Light conesLocal UnitaryEntanglementLocal Operations and Classical CommunicationQubitEntangled stateGreenberger-Horne-Zeilinger stateClassificationReduced density matricesRank...
- Two-component spinors are the basic ingredients for describing fermions in quantum field theory in four space-time dimensions. We develop and review the techniques of the two-component spinor formalism and provide a complete set of Feynman rules for fermions using two-component spinor notation. These rules are suitable for practical calculations of cross-sections, decay rates, and radiative corrections in the Standard Model and its extensions, including supersymmetry, and many explicit examples are provided. The unified treatment presented in this review applies to massless Weyl fermions and massive Dirac and Majorana fermions. We exhibit the relation between the two-component spinor formalism and the more traditional four-component spinor formalism, and indicate their connections to the spinor helicity method and techniques for the computation of helicity amplitudes.HelicityFeynman rulesRankQuantum field theorySupersymmetryLorentz transformationMajorana fermionStandard ModelMinimal supersymmetric Standard ModelDecay rate...
- The Hubble tension can be significantly eased if there is an early component of dark energy that becomes active around the time of matter-radiation equality. Early dark energy models suffer from a coincidence problem---the physics of matter-radiation equality and early dark energy are completely disconnected, so some degree of fine-tuning is needed in order for them to occur nearly simultaneously. In this paper we propose a natural explanation for this coincidence. If the early dark energy scalar couples to neutrinos then it receives a large injection of energy around the time that neutrinos become non-relativistic. This is precisely when their temperature is of order their mass, which, coincidentally, occurs around the time of matter-radiation equality. Neutrino decoupling therefore provides a natural trigger for early dark energy by displacing the field from its minimum just before matter-radiation equality. We discuss various theoretical aspects of this proposal, potential observational signatures, and future directions for its study.Early dark energyNeutrinoMatter-radiation equalityHubble constant tensionNeutrino massDark energyCosmic microwave backgroundCoincidence problemFifth forceMassive neutrino...
- In this paper, limits are set on bileptons masses and couplings in the context of the the 331 Model, as well as generic, non-331 Models predicting bileptons. The following measurable processes are studied: $pp \rightarrow \ell^{+}\ell^{+}\ell^{-}\ell^{-}X$, $pp \rightarrow \ell^{+}\ell^{-} \nu \nu X$ and $pp \rightarrow \ell^{+}\ell^{-} X$. Experimental limits on singly-charged bileptons masses and couplings within 331 Models are also obtained for the first time. With the results, an over 20 year-old experimental limit on vector bileptons is increased by 60\%. The computed limits are now the most stringent ones for these particles.Large Hadron ColliderATLAS Experiment at CERNInvariant massVector bosonStandard ModelTransverse momentumLeptoquarkMuonCharged leptonMissing transverse energy...
- Recent experimental data on several observables in semileptonic $B$-meson decays are found to be in tension with the corresponding Standard Model predictions. Most of these deviations are related to $b \to c$ and $b \to s$ flavour changing transitions. In this work, we estimate possible New Physics effects in $b \to d \mu^+ \mu^-$ flavour changing neutral currents. We parametrize NP contributions in a model-independent way and determine the allowed ranges of corresponding Wilson coefficients from the data on the exclusive $B^\pm \to \pi^\pm \mu^+ \mu^-$ decays measured recently by the LHCb collaboration. Afterwards, we investigate the impact of these results on other $b \to d$ processes such as the leptonic $B^0 \to \mu^+ \mu^-$ decays and $B^0 - \bar B^0$ mixing. As an example, we consider a simplified $Z^\prime$ model that is found to be consistent with current $b \to d$ data in the certain regions of the NP parameter space. In addition, we estimate the correlations between the partial decay widths of $B \to \pi \mu^+ \mu^-$ and $B \to K \mu^+ \mu^-$ processes to be used for an independent determination of CKM matrix elements as well as for a combined New Physics analysis of both $b \to d$ and $b \to s$ transitions.Standard ModelBranching ratioLHCb experimentCabibbo-Kobayashi-Maskawa matrixWilson coefficientsForm factorLight-cone sum rulesFlavour Changing Neutral CurrentsFlavourDecay width...
- Our recently proposed model of the $\Delta(1600)$ resonance, in which the dominant component is a quasi-bound state of the $\Delta(1232)$ and the pion, is confronted with a similar model of the $N^*(1440)$ resonance as its counterpart in the P11 partial wave. We stress an essentially different mechanism responsible for generating the two resonances.PionBound stateBare massCoupling constantScattering amplitudeRoper resonanceAttentionLattice calculationsBag Model of Quark ConfinementScattering matrix...
- That massless dark photons could exist and have flavor-changing magnetic-dipole couplings to down-type light quarks is an attractive possibility which may be realized in various new-physics scenarios. It is potentially testable not only in kaon processes but also via two-body hyperon decays involving missing energy carried away by the massless dark photon. We explore the latter within a simplified model approach and take into account constraints from the kaon sector. We find that the branching fractions of some of these hyperon modes are allowed to be as high as a few times $10^{-4}$. Such numbers are likely to be within the sensitivity reaches of ongoing experiments like BESIII and future ones at super charm-tau factories.HyperonHidden photonKaonBranching ratioMissing energyStandard ModelLight quarkFlavour Changing Neutral CurrentsStandard Model fermionLoop integral...