2018/2/27 (火)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Takeshi Kobayashi (SISSA)
Title: Baryons, Dark Matter, and Light Scalars
Abstract:
The appearance of scalar fields with small masses is ubiquitous in physics beyond the Standard Model. In this talk I will describe how such light scalars can play important roles in cosmology, especially in connection to the origin of the baryons and dark matter of our universe. With regard to the baryons, I will show that a scalar with an approximate shift symmetry, such as the QCD axion, can naturally induce baryogenesis. For dark matter, I will present cosmological constraints on scalar dark matter obtained from analyses of the Lyman-alpha forest and the cosmic microwave background; here I will particularly focus on the ultralight regime and examine the long-standing claim that ultralight scalar dark matter may solve the small-scale issues of the CDM paradigm.


2018/2/26 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
No seminar due to the entrance exam


2018/2/19 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
No seminar due to YKIS2018a Symposium


2018/2/12 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Holiday


2018/2/5 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Minxi He (RESCEU)
Title: Mass hierarchy in multi-field inflation and Higgs-R^2 inflation
Abstract:
Multi-field inflation models are able to give many interesting observable
features which are possibly to be detected by CMB and other observations
in the future. The general multi-field systems are difficult to solve analytically,
but in the presence of mass hierarchy, effective field theory can be used to
analyze the system. I will first review two papers arXiv: 1010.3693 and arXiv:
1205.0710 to derive the general formalism of multi-field inflation and the
effective field theory in the presence of mass hierarchy. Then I will talk
about my recent work, the application of this formalism to the two-field model
combining Higgs inflation and Starobinsky model.


2018/1/29 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Joint seminar at TiTech


2018/1/22 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker1: Eugeny Babichev (Laboratoire de Physique Théorique d'Orsay)
Title: Caustic free completion of k-essence
Abstract:
Both k-essence and the pressureless perfect fluid develop caustic
singularities at finite time. We explore the connection between the two
and show that they belong to the same class of models, which admits the
caustic free completion by means of the canonical complex scalar field.
Specifically, the free massive/self-interacting complex scalar
reproduces dynamics of pressureless perfect fluid/shift-symmetric
k-essence under certain initial conditions in the limit of large
mass/sharp self-interacting potential. We elucidate a mechanism of
resolving caustic singularities in the complete picture.

Speaker2: Eung Jin Chun (KIAS)
Title: Dark matter in Supersymmetric Axion Models
Abstract:
The strong CP problem is nicely resolved by the Peccei-Quinn mechanism which
predicts a light pseudo-Goldstone boson, the axion. It is a dark matter
candidate whose abundance is produced through the misalignment. In
supersymmetric theories, the fermionic partner of the axion, the axino,
is another dark matter candidate and can alter the standard features of a
neutralino dark matter candidate. In this talk, we discuss cosmological
and phenomenological properties of the axion supermultiplet and its impact on
the dark matter physics.


2018/1/15 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Teruaki Suyama (RESCEU)

On a paper
JCAP 1402 (2014) 019 (arXiv:1309.5888)
"Pulsar timing signal from ultralight scalar dark matter"
Andrei Khmelnitsky, Valery Rubakov.


2017/12/18 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Shun-Pei Miao (National Cheng Kung Univ.) [from 1:30 PM]
Title: Deducing Cosmological Observables from the S-matrix
Abstract:
We study one loop quantum gravitational corrections to the long range force induced by the exchange of a massless scalar between two massive scalars. The various diagrams contributing to the flat space S-matrix are evaluated in a general covariant gauge and we show that dependence on the gauge parameters cancels at a point considerably before forming the full S-matrix, which is unobservable in cosmology. It is possible to interpret our computation as a solution to the effective field equations --- which could be done even in cosmology --- but taking account of quantum gravitational corrections from the source and from the observer.


2017/12/11 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
No seminar due to CosPA2017


2017/12/4 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Keisuke Inomata (ICRR)
Title: Double Inflation as a single origin of PBHs for all dark matter and LIGO
Abstract:
Primordial Black Hole (PBH) is one of the leading non-particle candidates
for dark matter (DM).
Although several observations severely constrain the amount of PBHs,
it is recently pointed out that there is an uncertainty on the microlensing constraints
below ~ 10^{-10} M_\odot which was ignored originally
but may weaken the constraints significantly.
In the seminar, facing this uncertainty, we investigate the possibility that
PBHs can make up all DM in a broad mass spectrum.
Moreover, we propose a concrete inflation model which can simultaneously produce
PBHs for all DM in a broad mass spectrum around O(10^{-13}) M_\odot
and PBHs for LIGO events in a sharp mass spectrum at O(10) M_\odot.
This talk is based on our recent paper (arXiv:1711.06129).


2017/11/27 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
No seminar due to JGRG27


2017/11/20 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Toyokazu Sekiguchi (RESCEU)
Title: Abundance of dark matter axion in the coupling with dark photon
Abstract:
The axion and axion-like particles originate from a variety of UV theories based on QFT as well as string theory. Couplings of those axions with U(1) gauge fields are fairly ubiquitous. They are known to offer rich phenomenology in the very early Universe, for instance, inflation and preheating. In my talk I’m going to focus on their effects on the abundance of the QCD axion produced from the misalignment mechanism. It is recently argued that the coupling of the axion to a hidden U(1) field suppresses the axion abundance, which can open up the axion window up to the GUT scale. The claim postulates that production of the axion fluctuations is negligible. We revisit the argument by performing 3d lattice simulations of the axion electrodynamics, where the nonlinear dynamics in the coevolution of the axion fluctuations and gauge field is incorporated to the full extent. We show production of the axion fluctuations plays a crucial role and the suppression is moderated significantly.


2017/11/13 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Louis Yang (IPMU)
Title: Postinflationary Higgs Relaxation and Leptogenesis
Abstract:
The discovery of the Higgs boson with a mass of 125 GeV implies a relatively slow rise of the Standard Model Higgs potential at large energy scales. A scalar field with such a shallow potential can develop a large vacuum expectation value (VEV) during inflation through quantum fluctuation. The relaxation of the large VEV of the Higgs field after inflation may play an important role in the early stage of the universe. In this talk, I will talk about the generation of large Higgs VEV and how to do leptogenesis using the postinflationary relaxation of the Higgs field. I will also discuss one observable consequence of this relaxation leptogenesis model, which could explain the excess found in the cosmic infrared background (CIB) radiation anisotropy.


2017/11/6 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Joint seminar at IPMU


2017/10/30 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker1: Masaki Yamada (Tufts Univ.)
Title: On false vacuum decay catalyzed by black holes
Abstract:
False vacuum states are metastable in quantum field theories, and true vacuum bubbles can be nucleated due to the quantum tunneling effect. It was recently suggested that an evaporating Black Hole (BH) can be a catalyst of bubble nucleations and dramatically shortens the lifetime of the false vacuum. In particular, in the context of the Standard Model valid up to a certain energy scale, even a single evaporating BH may spoil the successful cosmology by inducing the decay of our electroweak vacuum. In this talk, we reinterpret catalyzed vacuum decay by BHs, using an effective action for a thin-wall bubble around a BH to clarify the meaning of bounce solutions. We calculate bounce solutions in the limit of a flat spacetime and in the limit of negligible backreaction to the metric, where it is much easier to understand the physical meaning, and compare these results with the full calculations done in the literature. As a result, we give a physical interpretation of the enhancement factor: it is nothing but the probability of producing states with a finite energy. This makes it clear that all the other states such as plasma should also be generated through the same mechanism, and calls for finite density corrections to the tunneling rate which tend to stabilize the false vacuum.

Speaker2: Ayuki Kamada (IBS)
Title: Galactic Rotation Curves with Dark Matter Self-Interactions
Abstract:
It has been shown that the LambdaCDM model can successfully explain large-scale structure of the universe. But it is not clear that it can accommodate observations on (sub-)galactic scales. In fact, the LambdaCDM model predicts dark matter halos, which are systematically denser than inferred from astrophysical observations. One interesting alternative assumes that dark matter particles are strongly interacting with each other. Dark matter self-interactions will lead to heat transfer from the hotter outer region to the cold inner region, reducing the central dark matter density. In this talk, I will show that the observed rotation curves of spiral galaxies are consistent with predicted in the SIDM model. I will also emphasize the importance of the baryonic disk in determining the SIDM halo profile.


2017/10/23 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Joint seminar at IPMU -> postponed to 11/6 due to a typhoon


2017/10/16 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
No seminar due to Kavli IPMU 10th anniversary symposium


2017/10/9 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Holiday


2017/10/2 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Jun'ichi Yokoyama (RESCEU)
Title: Spontaneous genesis after G-inflation
Abstract:
In kinetically driven G-inflation, the Universe after inflation
is dominated by the kinetic energy density of a free scalar field
whose energy density is dissipated in proportion to $a^{-6}$
so that the cosmic expansion law is like $a(t) \propto t^{1/3}$.
The reheating is achieved by gravitational particle production
or through direct coupling preserving the shift symmetry of the
model. We discuss spontaneous baryogenesis and asymmetric
dark matter genesis may be possible if these charge densities
have a derivative coupling with the inflaton.



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Last-modified: 2013-11-20 (水) 11:11:56 (1555d)