Hajime Fukuda, The University of Tokyo
On the direct detection of the QCD axion dark matter
Online (Zoom) https://kds.kek.jp/event/43767/ Because the axion is a pseudo-scalar Boson, as the interaction between axions and matter, spin-dependent interactions have been mainly discussed up to the present.
Because the axion is a pseudo-scalar Boson, as the interaction between axions and matter, spin-dependent interactions have been mainly discussed up to the present.
Spin-independent terms, which break the axion shift symmetry, are considered to be small, being suppressed by the axion mass.
However, we have found that couplings of 4-point interactions between nucleons and axions are not negligibly small.
The term is of particular importance for the axion dark matter, which has a long Compton length, because the scattering amplitude is enhanced by the coherent effect.
We discuss the consequences and the possible application of the interactions.
Tatsuya Amitani, Tokyo Institute of Technology
[QCD theory Seminar] Torsion-induced chiral magnetic current in equilibrium
Online (Zoom) We study equilibrium transport properties of massless Dirac fermions at finite temperature and chemical potential in spacetime accompanied by torsion, which in four dimensions couples with Dirac fermions as an axial gauge field. In particular, we compute the current density at the linear order in the torsion as well as in an external magnetic field with the Pauli-Villars regularization, finding that an equilibrium current akin to the chiral magnetic current is locally induced.
We study equilibrium transport properties of massless Dirac fermions at finite temperature and chemical potential in spacetime accompanied by torsion, which in four dimensions couples with Dirac fermions as an axial gauge field. In particular, we compute the current density at the linear order in the torsion as well as in an external magnetic field with the Pauli-Villars regularization, finding that an equilibrium current akin to the chiral magnetic current is locally induced.
Such torsion can be realized in condensed matter systems along a screw dislocation line, around which localized and extended current distributions are predicted so as to be relevant to Dirac and Weyl semimetals.
Furthermore, we compute the current density at the linear order in the torsion as well as in a Weyl node separation, which turns out to vanish in spite of being allowed from the symmetry perspective.
Hiroki Kawai, The University of Tokyo
[JpDe Joint Seminar] An analytic model for the structures in FDM halos
Online external homepage
Fuzzy dark matter is a hypothetical scalar particle whose mass is around 10^-22 eV, which is one of the alternatives to cold dark matter model to alleviate the small-scale problems. The quantum nature of FDM arises rich phenomena in small scale, such as soliton core and granular structures inside FDM halos.
For the first part in this talk, we focus on the granular structures and show an analytical model of the density profile. Using this model, we calculate a sub-galactic matter power spectrum and compare it with that obtained from the strong lens system SDSS J0252+0039.
Next we study how to determine a soliton core mass for a given halo mass. We compare the core-halo mass relation in our model and that obtained from the previous FDM simulations.
Motohiko Yoshimura, RIIS, Okayama University
Dynamical relaxation of cosmological constant and stronger gravity in the early universe
Online (Zoom) https://kds.kek.jp/event/43768/ Recent developments of early cosmology, inflation and late-time accelerating universe, are centered around the cosmological constant. It would be ideal if the fine-tuned cosmological constant problem is solved together with important cosmological issues including inflation, dark energy and cold dark matter. We shall discuss a possible framework to achieve this goal based on scalar-tensor gravity incorporating con formal coupling. In the proposed model the cosmological constant is elevated to a dynamical variable that evolves with cosmic expansion, and the inflaton motion may realize slow-roll inflation towards a potential minimum of a spontaneously broken phase and late-time roll-down to the point of zero cosmological constant at the field infinity. The key for this behavior is spontaneous symmetry breaking at inflation and symmetry restoration at later epochs. We shall discuss how these are realized and its inevitable consequence: strong gravity effects in the early universe, implying stronger gravitational wave emission and black hole formation of primordial origin. Cold dark matter consists of spatially inhomogeneous modes generated from thermal medium, and clumps made of cold dark matter may gravitationally collapse into primordial black holes which may constitute a part of cold dark matter. This talk is based on recent works listed below.
Recent developments of early cosmology, inflation and late-time accelerating universe, are centered around the cosmological constant. It would be ideal if the fine-tuned cosmological constant problem is solved together with important cosmological issues including inflation, dark energy and cold dark matter. We shall discuss a possible framework to achieve this goal based on scalar-tensor gravity incorporating con formal coupling. In the proposed model the cosmological constant is elevated to a dynamical variable that evolves with cosmic expansion, and the inflaton motion may realize slow-roll inflation towards a potential minimum of a spontaneously broken phase and late-time roll-down to the point of zero cosmological constant at the field infinity. The key for this behavior is spontaneous symmetry breaking at inflation and symmetry restoration at later epochs. We shall discuss how these are realized and its inevitable consequence: strong gravity effects in the early universe, implying stronger gravitational wave emission and black hole formation of primordial origin. Cold dark matter consists of spatially inhomogeneous modes generated from thermal medium, and clumps made of cold dark matter may gravitationally collapse into primordial black holes which may constitute a part of cold dark matter. This talk is based on recent works listed below.
References
[1] M. Yoshimura, “Dynamical relaxation of cosmological constant”, arXiv: 2204.10809 [hep-ph] (2022).
[2] M. Yoshimura, “Stronger gravity in the early universe”, arXiv: 2204.11384 [gr-qc] (2022).
[3] M. Yoshimura, “Bifurcated symmetry breaking in scalar-tensor gravity”, arXiv: 2112.02835v2 (2021);
Phys.Rev. D105, 083522 (2022).
Akinori Matsumoto, The University of Tokyo
Primordial He abundance from extremely metal-poor galaxies: Implications for the lepton asymmetry and the H0 tension
Online (Zoom) https://kds.kek.jp/event/43769/
The primordial He abundance is best determined by observations of metal-poor galaxies, while there are only a few known extremely metal-poor (< 0.1Z?) galaxies (EMPGs) having reliable He/H measurements. We present deep Subaru NIR spectroscopy for 10 EMPGs and determination of the He/H values with NIR HeI10830A line and optical emission lines. Adding pre-existing galaxies with reliable He/H estimates to our sample, we obtain Yp = 0.2379+/-0.0030, which is slightly (? 1σ) smaller than the previous values. With the Yp constrain, the existing primordial deuterium Dp constraints, and a prior of baryon-to-photon ratio η, we obtain the degeneracy parameter of electron-neutrino ξe = 0.05+/-0.03, the effective number of neutrino species Neff = 3.22+/-0.3, and η×10^10 = 6.13+/-0.04 from the Yp and Dp measurements. Our constraints suggest a lepton asymmetry and allow for a high value of Neff up to Neff = 3.55 within the 1σ level, which could mitigate the Hubble tension. This talk is based on the work presented in arXiv:2203.09617.
Luca V. Delacretaz, University of Chicago
[QCD theory Seminar] Nonlinear bosonization of Fermi liquids
Online (Zoom)
Landau’s theory of Fermi liquids is a cornerstone of theoretical physics. I will show how to formulate Fermi liquid theory as an effective field theory of bosonic degrees of freedom, using the formalism of coadjoint orbits. While at the linear level, this theory reduces to existing multidimensional bosonization approaches, it necessarily features nonlinear corrections that are fixed by the geometry of the Fermi surface. These are crucial to reproduce nonlinear response, such as higher-point functions of currents or densities. The effective field theory framework furthermore systematically parametrizes corrections to Fermi liquid behavior, and provides a new angle to approach non-Fermi liquids. (Based on https://arxiv.org/abs/2203.05004).
Daiki Ueda, Peking University
Entropy constraints on effective field theory
Online (Zoom) https://kds.kek.jp/event/42264/
Relative entropy is a non-negative quantity and depicts a difference between two probability distributions. In this talk, I explain constraints on perturbative corrections to the Euclidean effective action by the relative entropy. I show that the relative entropy can yield the constraints on some effective field theories generated by a class of UV theories with a specific sign of interactions between heavy and light degrees of freedom. For such a class of theories, I show that the interactions increase thermodynamic entropy at fixed energy and charge, which is intimately connected with the extremality relations of black holes exhibiting Weak-Gravity-Conjecture.
Sigtryggur Hauksson, IPHT, CEA-Saclay
[QCD theory Seminar] Jet broadening in a non-equilibrium QCD medium
Online (Zoom)
Heavy-ion collisions produce far-from-equilibrium QCD matter which rapidly becomes a hydrodynamic medium. In this talk, I discuss how jets are shaped by the initial stage of such collisions. Most importantly, I show that anisotropic momentum broadening of jets at early times leads to net spin in emitted gluons. This means that there is net spin polarization of jet partons which is constant at all energy scales. I furthermore discuss jet broadening in the later hydrodynamic stage. Using tools of non-equilibrium field theory, I show that momentum broadening is substantially reduced at lower transverse momenta compared with a medium in thermal equilibrium.
Kentaroh Yoshida, Kyoto University
Yang-Baxter sigma models from 4D Chern-Simons theory
Online (Zoom) https://kds.kek.jp/event/42173/
Recently, a 4D Cherns-Simons (CS) theory has been proposed by Costello and Yamazaki as a unified theory of 2D classically integrable field theories. In this talk, I will explain how to derive Yang-Baxter sigma models from this 4D CS theory.
Luca Visinelli, Tsung-Dao Lee Institute
[JpDe Joint Seminar] Axion Miniclusters in the Milky Way
Online external homepage
