セミナー 2022年

Simona Vegetti, Max Planck Institute

[JpDe Joint Seminar] Strong Gravitational Lensing as a Probe of Dark Matter

Online (Zoom)
The Cold Dark Matter model for structure formation is currently the most successful at reproducing many observations, but it remains largely untested in the non-linear sub-galactic regime. A clear prediction of this model is that a significant number of low-mass haloes should populate any galaxy and its line of sight. As most of these objects are expected to be completely dark, strong gravitational lensing provides a unique channel to detect them and determine the properties of dark matter by constraining the halo-mass function at the low-mass end.

Joshua Eby, IPUM

Probing Ultralight Dark Matter and the Very Local Density from Earth and Space

Online (Zoom) https://kds.kek.jp/event/43763/

Ultralight dark matter (ULDM) is known to form self-gravitating bound states through gravitational relaxation. There are intriguing hints in the literature suggesting similar dynamics might lead to overdensities in the solar system as well, with ULDM becoming bound to the Sun. These *Solar Halos* can be probed by experiments on Earth when their radius *R > 1 AU*, which implies ULDM particle masses *m < 10^{-14} eV.* For larger masses *m*, space-based missions on orbits within 1 AU can probe small, compact Solar Halos with exceptional reach; for scalar couplings probable in current and near-future atomic clock systems, the sensitivity can exceed that of Equivalence Principle tests and probe well-motivated space for natural scalar field models. I will review the state of the art on these topics, including several exciting NASA and international space missions that motivate searches aboard space probes.

Guido D'Amico, Parma University

The Cosmological Analysis of the SDSS/BOSS data from the EFTofLSS

Online (Zoom) https://kds.kek.jp/event/43764/
The Effective Field Theory of Large-Scale Structure is a perturbative formalism that allows us to predict the clustering of Cosmological Large-Scale Structure in the mildly non-linear regime in an accurate and reliable way. After a brief illustration of the theory, I will discuss recent results on its application to the analysis of galaxy clustering data.

Masahide Yamaguchi, Tokyo Inst. of Tech

Polychronic Tunneling: New Tunneling Processes Experiencing Euclidean and Lorentzian Evolution Simultaneously

Online (Zoom) https://kds.kek.jp/event/43765/
We discuss new possible tunneling processes in the presence of gravity.
We formulate quantum tunneling using the Wheeler-deWitt canonical quantization and the WKB approximation. The distinctive feature of our formulation is that it accommodates the coexistence of Euclidean and Lorentzian evolution. It opens up a new possibility of quantum tunneling; {¥it e.g.} a bubble wall itself tunnels the potential barrier pulling the field nearby, where the wall region experiences the Euclidean evolution while the other regions experience the Lorentzian evolution simultaneously.
We execute numerical analysis and find that such a process can have a much higher tunneling rate than that of the Coleman-De Luccia bounce. We also find that the new tunneling processes exist even in the decoupling regime of gravity and affect low energy phenomenology.

Joshua Ruderman, New York U

Dark Sector Prospects Away from Equilibrium

Online (Zoom) https://kds.kek.jp/event/43766/
Different Cosmologies for dark matter, or dark radiation, have different observational prospects. Standard Model particles were in thermal equilibrium at early times. But maybe the dark sector was not. In this talk I will discuss a few scenarios where particles are produced by non-equilibrium processes in the dark sector. I will show how dark matter, such as sterile neutrinos, could have been produced through an explosive period of exponential growth (similar to the spreading of a pathogen). I will also describe how radio photons can be produced by resonant oscillations of dark photons, as a possible explanation of the Arcade radio excess.

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.
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.
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.
[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.

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