Kinya Oda, Tokyo Woman's Christian University
New effect in wave-packet scatterings of quantum fields: Saddle points, Lefschetz thimbles, and Stokes phenomenon
Online (Zoom), indico page, slides (kek.jp only)
We find a new contribution in wave-packet scatterings, which has been overlooked in the standard formulation of S-matrix. As a concrete example, we consider a two-to-two scattering of light scalars ϕ by another intermediate heavy scalar Φ, in the Gaussian wave-packet formalism: ϕϕ→Φ→ϕϕ. This contribution can be interpreted as an “in-time- boundary effect” of Φ for the corresponding Φ→ϕϕ decay, proposed by Ishikawa et al., with a newly found modification that would cure the previously observed ultraviolet divergence. We show that such an effect can be understood as a Stokes phenomenon in an integral over complex energy plane: The number of relevant saddle points and Lefschetz thimbles (steepest descent paths) discretely changes depending on the configurations of initial and final states in the scattering.
Xin-Li Sheng, Central China Normal Univ.
[QCD theory Seminar] From Kadanoff-Baym to Boltzmann equations for massive spin-1/2 fermions
Online (Zoom)
The quark-gluon plasma (QGP) generated in high-energy heavy-ion collisions is the most vortical system human ever made. The orbital angular momentum of the system will be converted into spin polarization of quarks during the evolution of the QGP. In this work, we use a matrix-valued distribution function for massive spin-1/2 fermions. The diagonal part of this distribution is the particle number density and the remaining parts are spin polarization density in the rest frame. From the Kadanoff-Baym equation, we derive Boltzmann equations for the matrix-valued distribution function, where nonlocal collision terms appear at next-to-leading order in space-time gradient. The nonlocal terms contribute as sources for the spin polarization part of the matrix-valued distribution function. The Boltzmann equations we obtained pave the way for numerically simulating spin-transport processes involving spin-vorticity coupling.
Ryohei Kobayashi, ISSP, The University of Tokyo
Interacting fermionic topological phases with time reversal symmetry
Online (Zoom) https://kds.kek.jp/event/37875/
In this talk, we discuss a recipe to produce a lattice construction of fermionic topological phases of matter on unoriented spacetime, which plays a crucial role to study topological phases or anomalies based on the time reversal symmetry. As an application, we construct a gapped boundary for a large class of fermionic SPT phases protected by finite onsite symmetry, based on our path integral description in the presence of boundaries. We will also formulate a local path integral for the (1+1)d topological superconductor in class BDI classified by Z8, and discuss its application to the problem of finding non-local order parameter for the Z8 classification if time permits.
Jan Pawlowski, Heidelberg University
Emergent Hadrons and Diquarks
online (Zoom) indico page, slides (kek.jp only)
We discuss the emergence of a low-energy effective theory with quarks, mesons, diquarks and baryons at vanishing and finite baryon density from first principle QCD. The present work also includes an overview on diquarks at vanishing and finite density, and elucidates the physics of transitional changes from baryonic matter to quark matter including diquarks. This set-up is discussed within the functional renormalisation group approach with dynamical hadronisation. In this framework it is detailed how mesons, diquarks, and baryons emerge dynamically from the renormalisation flow of the QCD effective action. Moreover, the fundamental degrees of freedom of QCD, quarks and gluons, decouple from the dynamics of QCD below the respective mass gaps. The resulting global picture unifies the different low energy effective theories used for low and high densities within QCD, and allows for a determination of the respective low energy constants directly from QCD.
Hidetoshi Taya, RIKEN
[QCD Theory Seminar] How time-dependent electric fields affect the Schwinger mechanism?
Online (Zoom) The Schwinger mechanism, the vacuum pair production in the presence of strong electric fields, is one of the most remarkable predictions of strong-field QED. For a constant electric field, it was established by Schwinger in 1951 that the vacuum pair production is driven by quantum tunneling and the resulting production number is non-perturbatively suppressed. The constant electric field configuration is, however, too idealistic. Strong electric fields that may be realized in actual physical situations (e.g., intense lasers and heavy-ion
The Schwinger mechanism, the vacuum pair production in the presence of strong electric fields, is one of the most remarkable predictions of strong-field QED. For a constant electric field, it was established by Schwinger in 1951 that the vacuum pair production is driven by quantum tunneling and the resulting production number is non-perturbatively suppressed. The constant electric field configuration is, however, too idealistic. Strong electric fields that may be realized in actual physical situations (e.g., intense lasers and heavy-ion
collisions) must be time- (as well as space-) dependent. Thus, we need to go beyond Schwinger’s constant-field result.
In this talk, I discuss how time-dependence affects the vacuum pair production based on my works. In particular, I plan to discuss (1) the interplay between non-perturbative and perturbative pair production mechanisms and show that the widely-used Keldysh parameter is not the only parameter that controls the interplay [1, 2]; (2) dynamically assisted Schwinger mechanism and Franz-Keldysh effect in strong-field QED based on the perturbation theory in the Furry picture [3]; and (3) spin and chirality production by time-depending electric fields [4, 5, 6].
Refs:
[1] HT, H. Fujii, K. Itakura, PRD 90, 014039 (2014) [2] HT, T. Fujimori, T. Misumi, M. Nitta, N. Sakai, JHEP 03, 082 (2021) [3] HT, PRD 99, 056006 (2019) [4] X.-G. Huang, M. Matsuo, HT, PTEP 2019, 113B02 (2019) [5] X.-G. Huang, HT, PRD 100, 016013 (2019) [6] HT, PRR 2, 023257 (2020)
Sunao Sugiyama, IPMU, University of Tokyo
Exploring Dark Matter Candidates with Microlensing
Online (Zoom), indico page, slides (kek.jp only)
I will talk about constraints on dark matter (DM) candidates, especially primordial black hole (PBH), with optical microlensing search. Microlensing is a gravitational lensing phenomenon, caused purely by the gravitational effect, and is a powerful tool for studying the nature of dark matter. MACHO, Kepler, OGLE and Subaru HSC, have explored dark matter candidates until now. My project is to utilize current/future dataset of HSC to test various dark matter candidates, and to develop more sophisticated analysis method to study the nature of dark matter further. PBH is a viable candidate of dark matter, and has received attention these days, because it could also explain the counterparts of LIGO GW binary BH systems and the seed of super massive black holes that exist at nuclei of every galaxy. I will talk about a new PBH model proposed by us to account for these events as well as DM at the same time, and forecast of constraint on this model with HSC.
Nodoka Yamanaka, Kennesaw State University
[EX] Electric dipole moment and CP violation in many-body systems
Online (Zoom) The electric dipole moment (EDM) is an attractive experimental probe of CP violation beyond the standard model, and it may be measured in many systems such as the muon, neutron, atoms, and molecules.
The electric dipole moment (EDM) is an attractive experimental probe of CP violation beyond the standard model, and it may be measured in many systems such as the muon, neutron, atoms, and molecules.
An important physics to be understood is the many-body effect relating the elementary level (TeV scale) CP violation and the final EDM of the composite system to be measured.
In this talk, I review the current understanding of the many-body physics relevant in the context of the EDMs, focussing on the enhancement and suppression of the CP violation, and see the prospects for the discovery of new physics beyond the standard model.
Lee Roberts, Boston University
[EX] Exploring Terra Incognita with the World’s Largest Penning Trap
Online (Zoom) The Standard Model provides a very precise prediction of the muon’s magnetic anomaly aμ = (gμ – 2)/2, the deviation from 2 of the gyromagnetic ratio gμ. In his seminal 1926 paper, P.A.M. Dirac predicted that for electrons ge = 2, but experiments then revealed that ge was slightly larger than 2. The reason was to be found in Quantum Mechanics, and the first radiative correction to ge , calculated by Julian Schwinger, explained a deviation of order 0.1 %. Today, the Standard Model predicts the value of aμ to a precision of ± 0.36 parts per million (ppm). Dedicated experiments have measured aμ to ± 0.35 ppm precision. Therefore, precision measurements of the anomaly provide a stringent test of the Standard Model’s completeness, since Nature knows about all forces that could contribute to the muon’s magnetism, including those from New Physics that has not yet been discovered.
The Standard Model provides a very precise prediction of the muon’s magnetic anomaly aμ = (gμ – 2)/2, the deviation from 2 of the gyromagnetic ratio gμ. In his seminal 1926 paper, P.A.M. Dirac predicted that for electrons ge = 2, but experiments then revealed that ge was slightly larger than 2. The reason was to be found in Quantum Mechanics, and the first radiative correction to ge , calculated by Julian Schwinger, explained a deviation of order 0.1 %. Today, the Standard Model predicts the value of aμ to a precision of ± 0.36 parts per million (ppm). Dedicated experiments have measured aμ to ± 0.35 ppm precision. Therefore, precision measurements of the anomaly provide a stringent test of the Standard Model’s completeness, since Nature knows about all forces that could contribute to the muon’s magnetism, including those from New Physics that has not yet been discovered.
I will briefly review the intellectual history that began with the discovery of spin and the g-factor of the electron and its role on the development of Modern Physics. I will then focus on the new measurement of the muon magnetic anomaly that was recently reported by Fermilab experiment E989. The result determined from the first data set collected in 2017 has a precision of 0.46 ppm, and agrees well with the previous result obtained at Brookhaven National Laboratory at the beginning of this century. The combined experimental value exhibits tension with the Standard Model value.
Masanori Hanada, University of Surrey
Large-N limit as a second quantization
Online (Zoom) https://kds.kek.jp/event/37783/ In gauge/gravity duality, the information regarding the gravitational geometry (e.g., black hole and smooth exterior geometry) has to be encoded in gauge theory. Clearly, the color degrees of freedom (matrix degrees of freedom) should play the key role, because the duality can hold even when the gauge theory side is a matrix model. In this talk, I will provide a simple way of encoding the geometry to matrices, along the line of Witten’s work on the effective action of D-branes and strings, and the Matrix Theory conjecture by Banks, Fischler, Shenker and Susskind. Roughly speaking, eigenvalues of matrices can be identified with the location of the D-brane probe or extended objects such as black hole.
In gauge/gravity duality, the information regarding the gravitational geometry (e.g., black hole and smooth exterior geometry) has to be encoded in gauge theory. Clearly, the color degrees of freedom (matrix degrees of freedom) should play the key role, because the duality can hold even when the gauge theory side is a matrix model. In this talk, I will provide a simple way of encoding the geometry to matrices, along the line of Witten’s work on the effective action of D-branes and strings, and the Matrix Theory conjecture by Banks, Fischler, Shenker and Susskind. Roughly speaking, eigenvalues of matrices can be identified with the location of the D-brane probe or extended objects such as black hole.
Actually there is a famous argument against such simple interpretation advocated by Polchinski in 1998. His argument used generic properties of large-N gauge theory to show that the ground-state wave function delocalizes at large N, leading to a conflict with the locality in the bulk geometry. We show that this argument is not correct: the ground-state wave function does not delocalize, and there is no conflict with the locality of the bulk geometry. In order to understand how the old argument fails, recently-discovered connection between color confinement and Bose-Einstein condensation is useful. This confinement-BEC connection has a striking consequence: in the SU(N) gauge theory, there is a partially-deconfined phase in which an SU(M)-subgroup is deconfined. Partial deconfinement, combined with the “eigenvalue = location” picture, provides us with a natural scenario to realize the idea in BFSS Matrix Theory conjecture — extended objects, such as black hole, are realized as bound states of D-branes and strings, that look like non-commutative blocks in big matrices — in the Maldacena-type gauge/gravity duality. In the large-N limit, various many-body states can be realized by considering block-diagonal matrix configurations, just as in the BFSS proposal. Therefore, the large-N limit of gauge theory can be interpreted as the second quantization of the gravity side.
If time permits, we will discuss how we might be able to check this proposal quantitatively, via classical or quantum simulations.
Christof Wetterich, Heidelberg University
Pregeometry and emergent general relativity
Online (Zoom) https://kds.kek.jp/event/37782/
