セミナー

Tilo Wettig, University of Regensburg

Exact lattice chiral symmetry in 2d gauge theory

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom

Preserving the symmetries of massless fermions is a well-known challenge in lattice field theory. I’ll discuss symmetry-preserving lattice regularizations of 2d QED with one and two flavors of Dirac fermions, as well as the `3450′ chiral gauge theory. The construction leverages bosonization and recently-proposed modifications of Villain-type lattice actions. The internal global symmetries act just as locally on the lattice as they do in the continuum, the anomalies are reproduced at finite lattice spacing, and in each case we’ve found a sign-problem-free dual formulation.

Yohei Ema, University of Minnesota

On-shell reconstruction of massive scattering amplitudes

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom

In this talk, after reviewing the basics of the massive spinor helicity formalism, we introduce a momentum shift based on the helicity basis. This momentum shift allows an on-shell reconstruction of renormalizable theories with particles of any mass. As a demonstration of our method, we compute $e^+ e^- \to \mu^+ \mu^-$ and $W^+W^- \to W^+W^ $ amplitudes. An issue was raised on the former amplitude in literature and we see that, with our momentum shift, we can resolve the issue. In the latter case, we recover the correct amplitude, which contains the four-point contact interaction in terms of the Feynman diagrams, solely from the three-point amplitude. We see that this result is closely related to the Ward identity.

Koichi Hamaguchi, Tokyo University

Exploring Physics Beyond the Standard Model via Temperature Observations of Neutron Stars

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
In this seminar, I will talk about how temperature observations of neutron stars provide a unique window to explore physics beyond the Standard Model of particle physics. Neutron stars, with their extreme environments, serve as natural laboratories for testing the limits of our physical understanding. The standard cooling theory, which accounts for the cooling of isolated neutron stars through neutrino and electromagnetic radiation, generally aligns with observational data. However, the presence of hypothetical particles such as axions and dark matter, predicted by theories that extend the Standard Model, could alter this cooling behavior. Axions, for example, increase cooling rates, while dark matter interactions could lead to additional heating. By comparing revised theoretical predictions with observed temperature evolution, we might explore signs of these elusive particles. This talk is based on the following papers: arXiv:2309.02633, 2308.16066, 2204.
02413, 2204.02238, 2008.03924, 1905.02991, 1904.04667, 1806.07151.

Arnab Chaudhuri, National Astronomical Observatory of Japan

Dark matter production from two evaporating PBH distributions

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
Particulate dark matter (DM), completely isolated from the Standard Model particle sector, can be produced in the early Universe from primordial black hole (PBH) evaporation. However, big bang nucleosynthesis (BBN) observations put an upper bound on the initial mass of PBH requiring the PBH to evaporate completely before the advent of BBN. DM particles in the mass range ∼(1–10^9)GeV cannot explain the observed relic abundance for an early matter dominated universe due to this BBN constraint. However, this assumes the presence of only one monochromatic PBH mass distribution in the early Universe. In this talk, we will explore the simple possibility of achieving the observed relic with DM masses from the above mentioned range for an early matter dominated era with two monochromatic evaporating PBH mass distributions and demonstrate that the fermionic DM masses consistent with BBN change slightly.

Ryutaro Matsudo, NTU

Boundary condition and reflection anomaly in 2+1 dimensions

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
t is known that the 2+1d single Majorana fermion theory has an anomaly of the reflection, which is canceled out when 16 copies of the theory are combined. Therefore, it is expected that the reflection symmetric boundary condition is impossible for one Majorana fermion, but possible for 16 Majorana fermions. In this study, we consider a reflection symmetric boundary condition that varies at a single point, and find that there is a problem with one Majorana fermion. The problem is the absence of a corresponding outgoing wave to a specific incoming wave into the boundary, which leads to the non-conservation of the energy. For 16 Majorana fermions, it is possible to connect every incoming wave to an outgoing wave without breaking the reflection symmetry. In addition, we discuss the connection with the fermion-monopole scattering in 3+1 dimensions. This talk is based on arXiv:2306.10845.

羽澄昌史, 量子場計測システム国際拠点

[金茶会] 第7回 すべての量子を使い倒せ — QUPと宇宙・素粒子・社会

つくば:3号館セミナーホール (リモート会場:J-PARC研究棟2階会議室)

https://www-conf.kek.jp/kincha/

Jongkuk Kim, KIAS

Recent B->Kνν and muon g-2 anomalies in U(1)_{L_\mu - L_\tau}- charged DM model

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom

The Belle II collaboration recently announced that they observed the B → Kνν decay process for the first time. This dineutrino mode of B+ → K+ν¯ν has been theoretically identified as a very clean channel. However, their result encounters a 2.8σ deviation from the Standard Model (SM) calculation. On the other hand, last year, Fermilab released new data on muon (g − 2) away from the SM expectation with 5σ. In this talk, we will study the simplest UV-complete U(1)Lµ−Lτ -charged Dark Matter (DM) model.
Thanks to the existence of dark Higgs boson and dark photon in this model, we can explain the observed relic density of DM and resolve the anomalous results reported by both Belle II and Fermilab experiments simultaneously without any modification of the thermal history of the Universe.

Masanori Hanada, Queen Mary University of London

[QCD theory seminar] Color Confinement and Random Matrices

Oneine (Zoom)
We describe how the general mechanism of partial deconfinement applies to large-N QCD and the partially deconfined phase inevitably appears between completely-confined and completely-deconfined phases. Furthermore, we propose how the partial deconfinement can be observed in the real-world QCD with the SU(3) gauge group. For this purpose, we employ lattice configurations obtained by the WHOT-QCD collaboration and examine our proposal numerically. In the discussion, the Polyakov loop plays a crucial role in characterizing the phases, without relying on center symmetry, and hence, we clarify the meaning of the Polyakov loop in QCD at large N and finite N. As a nontrivial test for our proposal, we also investigate the relation between partial deconfinement and instanton condensation and confirm the consistency with the lattice data. As a nontrivial application, we show that computation of the two-point correlator of Polyakov loops in the confined phase reduces to the problem of random walk on group manifold. As a consequence, linear confinement potential with approximate Casimir scaling follows immediately.

Ten Brandes, Munich Tech U

Constraints on Phase Transitions in Neutron Star Matter

Online (Zoom)
Recent inference results of the sound velocity in the cores of neutron stars are summarized. Implications for the equation of state and the phase structure of highly compressed baryonic matter are discussed. In view of the strong constraints imposed by the heaviest known pulsars, the equation of state must be very stiff in order to ensure the stability of these extreme objects. This required stiffness limits the possible appearance of phase transitions in neutron star cores. For example, a Bayes factor analysis quantifies strong evidence for squared sound velocities c_s^2 > 0.1 in the cores of 2.1 solar-mass and lighter neutron stars. Only weak first-order phase transitions with a small phase coexistence density range \Delta\rho/\rho < 0.2 (at the 68\% level) in a Maxwell construction still turn out to be possible within neutron stars. The central baryon densities in even the heaviest neutron stars do not exceed five times the density of normal nuclear matter. In view of these data-based constraints, much discussed issues such as the quest for a phase transition towards restored chiral symmetry and the active degrees of freedom in cold and dense baryonic matter, are reexamined.

Aleskey Cherman, MInnesota U

Exact lattice chiral symmetry in 2d gauge theory

Online (Zoom)
Preserving the symmetries of massless fermions is a well-known challenge in lattice field theory. I’ll discuss symmetry-preserving lattice regularizations of 2d QED with one and two flavors of Dirac fermions, as well as the `3450′ chiral gauge theory. The construction leverages bosonization and recently-proposed modifications of Villain-type lattice actions. The internal global symmetries act just as locally on the lattice as they do in the continuum, the anomalies are reproduced at finite lattice spacing, and in each case we’ve found a sign-problem-free dual formulation.

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