セミナー 2023年

Tilo Wettig, University of Regensburg

Induced QCD

Hybrid On-site: Seminar room 321, 322 Online:(Zoom)
We explore an alternative discretization of continuum SU($N_c$) Yang-Mills theory on a Euclidean spacetime lattice, originally introduced by Budzcies and Zirnbauer. In this discretization the self-interactions of the gauge field are induced by a path integral over $N_b$ auxiliary boson fields, which are coupled linearly to the gauge field. The main progress compared to earlier approaches is that $N_b$ can be as small as $N_c$. We show analytically and numerically that the continuum limit of the new discretization reproduces Yang-Mills theory
and perform a perturbative calculation to match the bare parameter of the induced gauge theory to the standard lattice coupling. We also explore the possibility to integrate out the gauge fields to arrive at a dual formulation of lattice QCD.

Rafał Masełek, Warsaw University

Prospects for detecting long-lived particles at the Large Hadron Collider

Hubrid On-site: Seminar room 321, 322 Online:(Zoom)
The detection of the Higgs boson in 2012 raised hopes for rapid discovery of Physics Beyond the Standard Model at the LHC, however, the search for New Physics turned out to be much more difficult than anticipated. The lack of a positive result led to a growing interest in previously unexplored exotic signatures, e.g. long-lived particles. In the talk, I will discuss different search strategies for long-lived particles at the LHC. Special emphasis will be put on the prospects for the detection of long-lived particles in the MoEDAL experiment, which had been primarily designed to search for magnetic monopoles, but can also be utilised to detect semi-stable charged particles. Prospects for the detection of long-lived particles at the end of Run 3 and HL-LHC phases will be presented, and a comparison between different search strategies in MoEDAL, ATLAS and CMS experiments will be made.

Shi Chen, Univ. of Tokyo

[QCD theory Seminar] Solitonic symmetry beyond homotopy groups

Solitonic symmetry is believed to be classified by homotopy groups, but I will point out a more sophisticated algebraic structure. I shall focus on a concrete QFT, the 4d CP^1 model, and demonstrate that π_3 (CP^1) = Z does not lead to a U(1) 0-form solitonic symmetry. Actually, the invertible 0-form solitonic symmetry is a Z_2 which comes from Ω^spin_3 (CP^1) = Z_2. The complete 0-form solitonic symmetry is a non-invertible symmetry generated by 3d spin TQFTs.

Xu-Hui Jiang, HKUST

Testing Lepton Flavor Universality at Future Lepton Colliders

Hybrid On-site: Seminar room 321, 322 Online:(Zoom)
As one of the hypothetical principles in the Standard Model (SM), lepton flavor universality (LFU) should be tested with a precision as high as possible such that the physics violating this principle can be fully examined. The run of $Z$ factory at a future $e^+e^-$ collider such as CEPC or FCC-$ee$ provides a great opportunity to perform this task because of the large statistics and high reconstruction efficiencies for $b$-hadrons at $Z$ pole. In this paper, we present a systematic study on the LFU test in the future $Z$ factories. The goal is three-fold. Firstly, we study the sensitivities of measuring the LFU-violating observables of $b\to c \tau \nu$, {\it i.e.}, $R_{J/\psi}$, $R_{D_s}$, $R_{D_s^\ast}$ and $R_{\Lambda_c}$, where $\tau$ decays muonically. For this purpose, we develop the strategies for event reconstruction, based on the track information significantly. Secondly, we explore the sensitivity robustness against detector performance and its potential improvement with the message of event shape or beyond the $b$-hadron decays. A picture is drawn on the variation of analysis sensitivities with the detector tracking resolution and soft photon detectability, and the impact of Fox-Wolfram moments is studied on the measurement of relevant flavor events. Finally, we interpret the projected sensitivities in the SM effective field theory, by combining the LFU tests of $b\to c \tau \nu$ and the measurements of $b\to s \tau^+\tau^-$ and $b\to s \bar{\nu} \nu$. We show that the limits on the LFU-violating energy scale can be pushed up to $\sim \mathcal{O} (10)$~TeV for $\lesssim \mathcal O(1)$ Wilson coefficients at Tera-$Z$.

Goro Ishiki, University of Tsukuba

On the existence of the NS5-brane limit of the plane wave matrix model

Hybrid On-site: Seminar room 321, 322. Online:(Zoom)
We consider a double scaling limit of the plane wave matrix model (PWMM), in which the gravity dual geometry of PWMM reduces to a class of spherical NS5-brane solutions. We identify the form of the scaling limit for the dual geometry of PWMM around a general vacuum and then translate the limit into the field theoretic language. We also show that the limit indeed exists at least in a certain planar 1/4-BPS sector of PWMM by using the localization computation analytically. In addition, we employ the hybrid Monte Carlo method to compute the matrix integral obtained by the localization method, near the parameter region where the supergravity approximation is valid. Our numerical results, which are considered to be the first computation of quantum loop correction to the Lin-Maldacena geometry, suggest that the double scaling limit exists beyond the planar sector.

Priyanka Lamba, Warsaw University

Quantum information and CP measurement in "$H \rightarrow \tau^+ \tau^- $" at future lepton colliders

Hybrid On-site: Seminar room 321, 322 Online:(Zoom)
We introduce a methodology and investigate the feasibility of measuring quantum properties of tau lepton pairs in the H→τ+τ− decay at future lepton colliders. In particular, observation of entanglement, steerability and violation of Bell inequalities are examined for the ILC and FCC-ee. We find that detecting quantum correlation crucially relies on precise reconstruction of the tau leptons rest frame and a simple kinematics reconstruction does not suffice due to the finite energy resolution of the colliding beams and detectors. To correct for energy mismeasurements, a log-likelihood method is developed that incorporates the information of impact parameters of tau lepton decays. We demonstrate that an accurate measurement of quantum properties is possible with this method. As a by-product, we show that a novel model-independent test of CP violation can be performed and the CP-phase of Hττ interaction can be constrained with an accuracy comparable to dedicated analyses, i.e., up to 7.9∘ and 5.4∘ at ILC and FCC-ee, respectively.

Rajan Gupta, Los Alamos National Laboratory

The nucleon structure and contributions of novel CP violating interactions to the neutron electric dipole moment

Online (Zoom)
I will first introduce lattice QCD and how it allows the solution of the Feynman path integral formulation of quantum field theories using large scale numerical simulations. I will then describe how the calculations of nucleon correlations functions are performed. In the second part I will describe our recent results (charges, form factors, moments) on nucleon structure, the pion-nucleon sigma term and on the contributions of novel CP violating interactions (the theta term, quark EDM, quark chromo EDM) to the neutron electric dipole moment(EDM).

Wen Yin, Tohoku University

Broken Phase Sphaleron and Baryogenesis

Hybrid On-site: Seminar room 321, 322 Online:(Zoom)
We will explore baryogenesis scenarios in which the Universe is reheated to temperatures below 100 GeV. Such low temperatures may result from the decay of long-lived massive particles, which are found in various beyond Standard Model scenarios, or from a strongly first-order electroweak phase transition. Even if the reheating temperature is relatively low, the scattering of energetic particles in these scenarios can produce center-of-mass energies higher than the typical sphaleron mass. Optimistic estimates suggest that successful baryogenesis may be achievable for reheating temperatures as low as 0.1-1 GeV, provided that the sphaleron cross section is enhanced at high energies. Furthermore, a simple extension of the Standard Model can lead to sufficient baryon production by enhancing the W-boson coupling, even if more pessimistic estimates for the sphaleron rate are accurate. In both cases, collider and cosmic-ray experiments can probe the same process responsible for baryogenesis if the 2-to-many sphaleron reaction is significant enough.

Toru Kojo, Tohoku University

Sound velocity peak as a signature of quark matter formation

Online (Zoom)
Sound velocity characterizes how the stiffness of matter changes as density increases. Nuclear many-body calculations and nuclear constraints indicate that matter is soft up to 1-2n0 (nuclear saturation density), while neutron star observations require stiff matter around 3-5n0 to pass the so-called two-solar mass constraint. This suggests that the QCD equation of state must have soft-to-stiff evolution in the interval of 2-5n0. Purely nuclear matter calculations typically lead to gentle stiffening to ~5n0.. We argue that the quark substructure of baryons is important even before baryons substantially overlap, leading to rapid stiffening and the sound velocity peak. These features are implemented in the Quark-Hadron-Crossover (QHC) equation of state (EOS). Using this EOS we study neutron star observables, in particular, gravitational waves in the post-merger phase, and quantify how large the impact of the sound velocity peak can be.

John Ellis, King's College

Atom Interferometer experiments to search for ultralight dark matter and gravitational waves

Hybrid On-site: Seminar room 321, 322. Online:(Zoom)
Atom interferometers measure the quantum interference between cold atoms in clouds following different space-time trajectories, which is sensitive to phase shifts induced by interactions with ultralight dark matter or the passage of gravitational waves. The capabilities of atom interferometers will be illustrated by their estimated sensitivities to the possible couplings of ultralight dark matter to electrons and photons, and to gravitational waves in the frequency range around 1 Hz intermediate between the peak sensitivities of the LIGO and LISA experiments. The latter open a window on mergers of masses intermediate between those discovered by the LIGO and Virgo experiments and the supermassive black holes present in the cores of galaxies, as well as fundamental physics processes in the early Universe.

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