2022.12.09 14:00-15:00
Speaker: Wen-Cong Yang
Time: Dec 9th Friday, 2:00-2:30pm
Title: Back and Forth: Reverse Phase Transitions in Numerical Relativity Simulations
Abstract: Although it is known from quantum chromodynamics that hadronic matter will undergo a phase transition to exotic forms of matter, e.g., quark matter, the onset density of such a phase transition cannot be computed from first principles. Hence, it remains an open question if such phase transitions occur inside isolated neutron stars or during binary neutron star mergers, or if they appear at even higher densities that are not realized in the Cosmos. In this article, we perform numerical-relativity simulations of neutron-star mergers and investigate scenarios in which the onset density of such a phase transition is exceeded in at least one inspiralling binary component. Our simulations reveal that shortly before the merger it is possible that such stars undergo a “reverse phase transition”, i.e., densities decrease and the quark core inside the star disappears leaving a purely hadronic star at merger. After the merger, when densities increase once more, the phase transition occurs again and leads, in the cases considered in this work, to a rapid formation of a black hole. We compute the gravitational-wave signal and the mass ejection for our simulations of such scenarios and find clear signatures that are related to the postmerger phase transition, e.g., smaller ejecta masses due to the softening of the equation of state through the quark core formation.
Ref. arXiv:2211.04662.
Speaker: Yongshun Hu
Time: Dec 9th Friday, 2:30-3:00pm
Title: Molecular Interactions Induced by a Static Electric Field in Quantum Mechanics and Quantum Electrodynamics
Abstract: By means of quantum mechanics and quantum electrodynamics applied to coupled harmonic Drude oscillators, we study the interaction between two neutral atoms or molecules subject to a uniform static electric field. Our focus is to understand the interplay between leading contributions to field-induced electrostatics/polarization and dispersion interactions, as considered within the employed Drude model for both non-retarded and retarded regimes. For the first case, we present an exact solution for two coupled oscillators obtained by diagonalizing the corresponding quantum-mechanical Hamiltonian and demonstrate that the external field can control the strength of different intermolecular interactions and relative orientations of the molecules. In the retarded regime described by quantum electrodynamics, our analysis shows that field-induced electrostatic and polarization energies remain unchanged (in isotropic and homogeneous vacuum) compared to the non-retarded case. For interacting species modeled by quantum Drude oscillators, the developed framework based on quantum mechanics and quantum electrodynamics yields the leading contributions to molecular interactions under the combined action of external and vacuum fields.
This topic is based on the paper [J. Phys. Chem. Lett. 13, 2197−2204 (2022)].
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2022.12.02 14:00-15:00
Speaker: Bing-Dong Wan
Time: Dec 2nd Friday, 2:00-2:30pm
Title: Light baryonium spectrum
Abstract: Deuteron, created at the beginning of the Universe and its stability is responsible for the production of other elements, is a typical and well- established dibaryon molecular state with JP = 1+ and binding energy EB = 2.225 MeV. Interestingly, the strong interactions bring stability to deuterons and also allow various other stable deuteronlike dibaryon states; however, no such states, though speculated about many times, have been observed yet. Since the interaction between baryon-antibaryon pair is analogous to that between two baryons, the studies on baryonium (baryon-antibaryon) will provide important hints to understanding the absence in observation of the stable deuteronlike dibaryon states. In this talk, I will introduce the light baryonium spectrum based on PRD 105, 014016 (2022) and the observation in experiments based on arXiv:2211.10755.
Speaker: Jia-Jun Wu
Time: Dec 2nd Friday, 2:30-3:00pm
Title: Axion-like Particles Explanation of High-energy Photons from GRB 221009A
Abstract: Recent astrophysical transient Swift J1913.1+1946 is possibly associated with the gamma-ray burst GRB 221009A at the redshift z ≈ 0.151. The transient was accompanied by very high-energy gamma rays up to 18 TeV observed by LHAASO and a photon-like air shower of 251 TeV detected by Carpet-2. These energetic gamma rays cannot reach us from the claimed distance of the source because of the pair production on cosmic background radiation. If the identification and redshift measurements are correct, one would require new physics to explain the data. One possibility invokes axion-like particles (ALPs) which mix with photons but do not attenuate on the background radiation. I will briefly introduce a related paper I have read recently.
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2022.11.25 14:00-15:00
Speaker: Linghui Hou
Time: November 25th Friday, 2:00-2:30pm
Title: Uniqueness from gauge invariance and the Adler zero
Abstract: In this talk I will introduce the uniqueness of gauge (EFT) amplitudes from gauge invariance (Adler zero). Yang-Mills and General Relativity tree-level amplitudes are completely determined by gauge invariance in n − 1 particles, with minimal assumptions on the singularity structure. Similiarly scalar non-linear sigma model and Dirac-Born-Infeld tree-level amplitudes are fixed by imposing full locality and the Adler zero condition (vanishing in the single soft limit) on n − 1 particles. Furthermore, without the assumption of the singularity structure there is a maximally constrained gauge invariance alone leads to both locality and unitarity.
Speaker: Bing-Kai Sheng
Time: November 25th Friday, 2:30-3:00pm
Title: Fate of first-order chiral phase transition in QCD: Implications to dark QCD
Abstract: The phase structure of the thermal and dense QCD matter in an external magnetic field has extensively been explored and the first-order nature of the chiral phase transition in QCD-like theories can play crucial roles to address a dark side of the Universe, where the created out-of equilibrium is essential to serve as cosmological and astrophysical probes such as gravitational wave productions. This interdisciplinary physics is built based on a widely-accepted conjecture that the thermal chiral phase transition in QCD-like theories with massless (light) three flavors is of first-order. In this work, however, the authors find that such a first-order feature may not hold, when ordinary or dark quarks are externally coupled to a weak enough background magnetic field. They work on the three flavor Nambu—Jona-Lasinio(NJL) model coupled to an external background magnetic field and the electromagnetic scale anomaly is incorporated. The disappearance of the first-order chiral transition is the generic consequence of the presence of the magnetically induced scale anomaly and the magnetic catalysis for the chiral symmetry breaking, and would impact or constrain modelling dark QCD coupled to an external magnetic field. Ref. arXiv:2208.03975 or PhysRevD.106.095010 .
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2022.11.18 14:00-15:00
Speaker: Yuanhao Zhang
Time: November 18th Friday, 2:00-2:30pm
Title: MLGWSC-1: The first Machine Learning Gravitational-Wave Search Mock Data Challenge
Abstract: We present the results of the first Machine Learning Gravitational-Wave Search Mock Data Challenge (MLGWSC-1). For this challenge, participating groups had to identify gravitational-wave signals from binary black hole mergers of increasing complexity and duration embedded in progressively more realistic noise. The final of the 4 provided datasets contained real noise from the O3a observing run and signals up to a duration of 20 seconds with the inclusion of precession effects and higher order modes. We present the average sensitivity distance and runtime for the 6 entered algorithms derived from 1 month of test data unknown to the participants prior to submission. Of these, 4 are machine learning algorithms. We find that the best machine learning based algorithms are able to achieve up to 95% of the sensitive distance of matched-filtering based production analyses for simulated Gaussian noise at a false-alarm rate (FAR) of one per month. In contrast, for real noise, the leading machine learning search achieved 70%. For higher FARs the differences in sensitive distance shrink to the point where select machine learning submissions outperform traditional search algorithms at FARs ≥200 per month on some datasets. Our results show that current machine learning search algorithms may already be sensitive enough in limited parameter regions to be useful for some production settings. To improve the state-of-the-art, machine learning algorithms need to reduce the false-alarm rates at which they are capable of detecting signals and extend their validity to regions of parameter space where modeled searches are computationally expensive to run. Based on our findings we compile a list of research areas that we believe are the most important to elevate machine learning searches to an invaluable tool in gravitational-wave signal detection. Ref. 2209.11146.
Speaker: Wen-Hong Ruan
Time: November 18th Friday, 2:30-3:00pm
Title: Rapid parameter estimation for an all-sky continuous gravitational wave search using conditional variational auto-encoders
Abstract: In this work, the authors extend the SOAP search to return broad Bayesian posteriors on the astrophysical parameters of a specific continuous gravitational-wave (CW) signal model. Their method uses a machine learning technique, specifically a conditional variational auto-encoder, and delivers a rapid estimation of the posterior distribution of four Doppler parameters of a CW signal. Their result indicates that the Doppler parameter space volume can be reduced by a factor of O(10^-7) for signals of SNR 100. Ref: 2209.02031.
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2022.11.11 14:00-15:00
Speaker: Jiaming Shi
Time: November 11th Friday, 2:00-2:30pm
Title: Cosmological constraints from the Hubble diagram of quasars at high redshifts
Abstract: The concordance (LambdaCDM) model reproduces the main current cosmological observations assuming the validity of general relativity at all scales and epochs, the presence of cold dark matter, and of a cosmological constant, equivalent to a dark energy with constant density in space and time. However, the LambdaCDM model is poorly tested in the redshift interval between the farthest observed Type Ia supernovae5 and that of the Cosmic Microwave background (CMB). We present new measurements of the expansion rate of the Universe in the range 0.5<z<5.5 based on a Hubble diagram of quasars. The quasar distances are estimated from their X-ray and ultraviolet emission, following a method developed by our group. The distance modulus-redshift relation of quasars at z<1.4 is in agreement with that of supernovae and with the concordance model. Yet, a deviation from the LambdaCDM model emerges at higher redshift, with a statistical significance of ~4 sigma. If an evolution of the dark energy equation of state is allowed, the data suggest a dark energy density increasing with time.
Ref: G. Risaliti & E. Lusso, Nature Astronomy 3, 272–277 (2019), arXiv:1811.02590.
Speaker: Fu-Guo Yang
Time: November 11th Friday, 2:30-3:00pm
Title: A Brief Introduction to Holographic Superconductivity and Some recent Developments
Abstract: The AdS/CFT correspondence argued that a classical scalar-gravity model describes a superconducting phase transition in a dual strongly interacting field theory. This argument raises the hope that one might get lessons from such theories to real condensed matter systems.
According to some work progress, one can believe that the holographic superconductor model indeed catch some physics for the real condensed matter systems. Besides, there are many interesting dynamics arise in the holographic superconductor model and have yet to find holographic connection to field theory side. Fail or hope to real matter systems? The answer is still in veil.
In this journal club, I will introduce how to construct holographic superconductor in details and briefly discuss several kinds of superconductor model. Then, about the dynamics and developments, I will give a brief summary for it.
Key papers：0810.1563; 1502.00437; 2006.10056; hep-th/0212256; 2009.05520.
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2022.11.04 14:00-15:00
Speaker: Xiang-Nan Jin
Time: November 4th Friday, 2:00-2:30pm
Title: CP violation in b→sll: a model independent analysis
Abstract: This work performs a model-independent global fit to all experimental data of b→sll assuming new physics couplings to be complex. They identify scenarios which provide a good fit to the data. The complex magnitudes are reflected in direct CP asymmetry in B→Κμ+μ- along with a number of angular CP asymmetries in B0→Κ0* μ+μ- decay. They examine the sensitivities of these observables to various solutions, which are different in the low and high-q2 bins. The precise measurement of direct CP asymmetries and angular CP asymmetries observables can not only confirm the existence of additional weak phases but can also enable an unique determination of Lorentz structure of possible new physics in b→sμ+μ- transition.
Speaker: Yu-Mei Wu
Time: November 4th Friday, 2:30-3:00pm
Title: Exploring Realistic Nanohertz Gravitational-Wave Backgrounds
Abstract: Hundreds of millions of supermassive black hole binaries are expected to contribute to the gravitational-wave signal in the nanohertz frequency band. Their signal is often approximated either as an isotropic Gaussian stochastic background with a power-law spectrum, or as an individual source corresponding to the brightest binary. In reality, the signal is best described as a combination of a stochastic background and a few of the brightest binaries modeled individually. We present a method that uses this approach to efficiently create realistic pulsar timing array datasets using synthetic catalogs of binaries based on the Illustris cosmological hydrodynamic simulation. We explore three different properties of such realistic backgrounds, which could help distinguish them from those formed in the early universe: i) their characteristic strain spectrum; ii) their statistical isotropy; and iii) the variance of their spatial correlations. We also investigate how the presence of confusion noise from a stochastic background affects detection prospects of individual binaries. We calculate signal-to-noise ratios of the brightest binaries in different realizations for a simulated pulsar timing array based on the NANOGrav 12.5-year dataset extended to a time span of 15 years. We find that ∼ 8% of the realizations produce systems with signal-to-noise ratios larger than 5, suggesting that individual systems might soon be detected (the fraction increases to ∼ 32% at 20 years). These can be taken as a pessimistic prediction for the upcoming NANOGrav 15-year dataset, since it does not include the effect of potentially improved timing solutions and newly added pulsars. Ref: arXiv:2207.01607.
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2022.10.28 14:00-15:00
Speaker: Chang Hu
Time: October 28th Friday, 2:00-3:00pm
Title: Classical impulse from Scattering Amplitudes
Abstract: Scattering amplitudes have their origin in quantum field theory, but have wide-ranging applications extending to classical physics. We review a formalism to connect certain classical observables to scattering amplitudes. The advantage of this formalism is that it enables us to study implications of the double copy in classical gravity. We discuss examples of observables including the total change of a particle’s momentum, and the gravitational waveform, during a scattering encounter. We will focus on the details of the classical impulse of electromagnetic case as an example. We can parallel to do the gravitational waveform.
Refs. 2203.13025, 2107.10193, 1906.09260.
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2022.10.14 14:00-15:00
Speaker: Chi-Wei Liu
Time: October 14th Friday, 2:00-2:30pm
Title: The strangest lifetime: A bizarre story of τ(Ωc)
Abstract: In this week of the journal club, I will like to talk about the story of the Ωc lifetime, which is recently found to be 4 times larger than the one in 2004 at LHCb and Belle. The main references of this talk are arXiv : 2001.06908, 2111.09566, and 2204.11935. Hope you enjoy!
Speaker: Jiabao Zhang
Time: October 14th Friday, 2:30-3:00pm
Title: EMC effect and Polarized gluon distribution in models based on Holographic Light-Front QCD
Abstract: In this talk, I will introduce two papers recently submitted to arXiv: 2209.13753, 2209.14285. They are dedicated to different scientific problems: EMC effect and proton spin puzzle, which are unsolved problems in nuclear physics and particle physics, respectively. These works both base on the holographic Light-Front QCD(HLFQCD), this is why I choose to present them in the same time.
The first paper present a new model based on HLFQCD. They find out that the EMC effect is a result of SU(6) symmetry breaking in this model.
The second one obtain the gluon Parton Distribution Functions(PDFs) in the extended framework of HLFQCD. They predict the gluon helicity contribution to the proton spin as $\Delta G=0.221^{+0.009}_{-0.010}$.
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2022.09.30 14:00-15:00
Speaker: Yuan Tao
Time: September 30th Friday, 2:00-2:30pm
Title: Plausible presence of quark matter in neutron stars with masses above 0.97 M_{TOV}
Abstract: Whether there is a quark matter core in the neutron star (NS) is a fundamental question. The increasing multi-messenger data set of NSs provide a valuable chance to examine such an attractive possibility. Here we carry out the Bayesian nonparametric inference of the NS equation of state (EOS) via a single-layer feed-forward neural network, taking into account the data of GW170817, PSRJ0030+0451, and PSRJ0740+6620, and incorporating the latest constraints from the chiral effective theory and perturbative quantum chromodynamics at low and very high energy densities, respectively. It is found out that a sizable quark matter core (≥ 0.001M⊙) is plausible (≥ 90% probability) for the very massive NS with a gravitational mass above about 0.97M_{TOV} , where M_{TOV} , the maximum gravitational mass of a non-rotating cold NS, is simultaneously constrained to be 2.18^{+0.27}_{-0.13} M⊙ (90%credibility). The average density of the quark matter core is found to be approximately 2.2 times that of the host NS. A few percent of the posterior EOSs, which do not predict quark matter cores even in the heaviest NSs, are characterized by a quicker rising of sound speed at relatively low densities. We also find that sound speed may reach close to zero near the center density of NS with M ∼ M_{TOV} and hence only allows the presence of the strong first-order phase transition in the center of the most massive NSs.
Speaker: Zheng-Yi Wei
Time: September 30th Friday, 2:30-3:00pm
Title: Pursuit of CP violation in hyperon decays at e +e − colliders
Abstract: In this talk , I will introduce a paper by Xiao-Gang He and his collaborators.They present a concise overview on CP violation in hyperon decays , compare the experiment data reported by BESIII with corresponding current predictions for CP asymmetries within the SM, and how much these asymmetries might be enhanced by possible new physics beyond the SM.
Ref: https://arxiv.org/abs/2209.04377
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2022.09.16 14:00-15:00
Speaker: Tian-Wei Wu
Time: September 16th Friday, 2:00-2:30pm
Title: Doubly heavy baryons and tetraquarks predicted by constituent quark model
Abstract: In this talk, I will introduce the constituent quark model proposed by Karliner and his collaborators and explain how this model is used to predict the masses of doubly heavy baryons $\Xi_{cc}$ and tetraquarks $T_{cc}$, which are successively confirmed by later experiments.
Refs: PRD 90, 094007 (2014), PRL 119, 202001 (2017)
Speaker: Geng Li
Time: September 16th Friday, 2:30-3:00pm
Title: New Insights Into Axion-Lepton Interactions
Abstract: We revisit the theory and constraints on axion-like particles (ALPs) interacting with leptons. We clarify some subtleties in the constraints on ALP parameter space and find several new opportunities for ALP detection. We identify a qualitative difference between weak-violating and weak-preserving ALPs, which dramatically change the current constraints due to possible ``energy enhancements'' in various processes. This new understanding leads to additional opportunities for ALP detection through charged meson decays W boson decays. The new bounds impact both weak-preserving and weak-violating ALPs and have implications for the QCD axion and addressing experimental anomalies using ALPs.
Ref: https://arxiv.org/abs/2209.00665
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2022.09.02 14:00-15:00
Speaker: Yao Ma
Time: September 2nd Friday, 2:00-2:30pm
Title: A short discussion on amplitude decompositions and related singularity structures
Abstract: In modern quantum physics, physical phenomenons stem from the singularities of scattering amplitudes, so it’s useful to acknowledge the structures of those amplitudes one cares about. At meantime, experimental observables are always obtained from partial wave analysis so that the importance of understanding the structures of partial wave amplitudes become more and more pressing. In practice, only right hand parts of partial wave amplitudes can be fit well at physical regions where experimental data are located, meanwhile left hand cuts can also contribute to physics significantly as backgrounds. But in most analysis these backgrounds, which present the crossing channel singularities, are treated as some arbitrary polynomials which may lead to less serious conclusions. In this weak discussion, I want to give a brief introduction to a method, Roy-Steiner equation, which may solve left hand singularities more rigorous and some basic examples (pi pi scattering and pi-N scattering processes) will also be given for illustration. Before the process of handling partial wave singularity analysis, amplitude decomposition will make calculation more neat, so this topic will also be discussed briefly.
The contents are mainly based on Refs listed below:
[1] Hoferichter, M., Elvira, J. R. de, Kubis, B. & Meißner, U.-G. Roy–Steiner-equation analysis of pion–nucleon scattering. Phys Reports 625, 1–88 (2016).
[2] Scadron, M. D. & Jones, H. F. Covariant M Functions for Higher Spin. Phys Rev 173, 1734–1744 (1968).
Speaker: Ziyu Tang
Time: September 2nd Friday, 2:30-3:00pm
Title: Stringent axion constraints with Event Horizon Telescope polarimetric measurements of M87*
Abstract: The hitherto unprecedented angular resolution of the Event Horizon Telescope has created exciting opportunities in the search for new physics. Recently, the linear polarization of radiation emitted near the supermassive black hole M87 ⋆ was measured on four separate days, precisely enabling tests of the existence of a dense axion cloud produced by a spinning black hole. The presence of an axion cloud leads to a frequency-independent oscillation in the electric vector position angle of this linear polarization. For the nearly face-on M87 ⋆ , this oscillation in the electric vector position angle appears as a propagating wave along the photon ring. In this paper, we leverage the azimuthal distribution of electric vector position angle measured by the Event Horizon Telescope to study the axion–photon coupling. We propose a novel differential analysis procedure to reduce the astrophysical background, and derive stringent constraints on the existence of axions in the previously unexplored mass window of ~(10 −21 –10 −20 ) eV.
[3] Y. Chen, Y. Liu, R.S. Lu, Y. Mizuno, J. Shu, X. Xue, Q. Yuan and Y. Zhao, Nature Astron. 6 (2022) 5, 592-598
