New Directions in Cosmology

24 Mar 2020, 08:00 → 27 Mar 2020, 17:30 Asia/Tokyo

Faculty of Science Bldg. 1 East: Room 285 (Hongo Campus)

Due to the concern regarding the coronavirus COVID-19, the workshop is cancelled.

We are pleased to announce the international workshop "New Directions in Cosmology.” The aim of the workshop is to bring together experts and to exchange ideas in cosmology, astroparticle physics, and related subjects in particle physics.

Dates and venue

Dates: March 24-27, 2020
Venue: Room 285, Faculty of Science Bldg.1 East, Hongo Campus, The University of Tokyo.

 

Important dates

Abstract submission deadline: Jan. 10, 2020 (closed)
Registration deadline: Jan. 31, 2020 (closed)

 

Speakers include:

Tobias Binder (Kavli IPMU)
Kfir Blum (CERN; Weizmann Institute of Science)
Gongjun Choi (TDLI)
Nagisa Hiroshima (Univ. of Toyama; iTHEMS, RIKEN)
Kenta Hotokezaka (Princeton Univ.; RESCEU)
Alejandro Ibarra (TUM)
Kiyotomo Ichiki (Nagoya Univ.; KMI)
Koji Ishiwata (Kanazawa Univ.)
Akito Kusaka (Univ. of Tokyo)
Tongyan Lin (UC, San Diego)
Kohta Murase (Pennsylvania State Univ.)
Seong Chan Park (Yonsei University)
Nirmal Raj (TRIUMF)
Kenichi Saikawa (Kanazawa Univ.)
Yevgeny Stadnik (Kavli IPMU)
Tomo Takahashi (Saga Univ.)
Kenneth C. Wong (Kavli IPMU)

 

 

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Organizers:

Koichi Hamaguchi (co-chair, Physics Department, Tokyo U. )
Takeo Moroi (co-chair, Physics Department, Tokyo U. )
Natsumi Nagata (Physics Department, Tokyo U.)
Kazunori Nakayama (Physics Department, Tokyo U.)
Tom Melia (IPMU)
Shigeki Matsumoto (IPMU)
Tsutomu Yanagida (IPMU, TDLI)
Javier Menendez (University of Barcelona)
Kentaro Nagamine (Osaka)
Satoshi Iso (KEK)
Masahiro Yamaguchi (Tohoku)

 

Sponsored by

Grant-in-Aid for Scientific Research on Innovative Areas 
19H05810: https://kaken.nii.ac.jp/en/grant/KAKENHI-PLANNED-19H05810/
16H06490: https://kaken.nii.ac.jp/en/grant/KAKENHI-PLANNED-16H06490/

 

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Tuesday 24 March

09:20 → 09:50 Registration

09:50 → 10:00 Opening

10:00 → 10:40 Invited talks

10:00 Is there a supernovae bound on axions?

We consider the SN1987A supernova cooling bound on axions and other light particles. Core collapse simulations used in the literature to substantiate the bound omitted from the calculation the envelope exterior to the proto-neutron star (PNS). As a result, the only source of neutrinos in these simulations was, by construction, a cooling PNS. We show that if the delayed neutrino mechanism failed to explode SN1987A, and if the pre-collapse star was rotating, then an accretion disk would form that could explain the late-time (t>5 sec) neutrino events. Such accretion disk would be a natural feature if SN1987A was a collapse-induced thermonuclear explosion. Axions do not cool the disk and do not affect its neutrino output, provided the disk is optically-thin to neutrinos, as it naturally is. These considerations cast doubt on the supernova cooling bound.

Speaker: Kfir Blum (Weizmann Institute & CERN)

11:10 → 12:30 Invited talks

11:10 Nucleons, Electrons, and Pasta: Discovering Dark Matter by Reheating the Neutron Star Soup

I present a largely model-independent probe of dark matter interactions with nucleons and electrons. Accelerated by gravity to relativistic speeds, local dark matter scattering against old neutron stars deposits kinetic energy at a rate that heats them to infrared blackbody temperatures. The resulting radiation is detectable by next generation telescopes such as James Webb, the Thirty Meter Telescope, and the European Extremely Large Telescope. I treat neutron star capture of dark matter by scattering (a) in the various layers of the well-understood stellar crust, on nucleonic and nuclear constituents, which include non-spherical "pasta" phases, (b) in the less understood stellar core, on nucleons and muons using non-relativistic kinematics, and on electrons using relativistic kinematics. I show that the (non-)observation of dark kinetic heating of neutron stars would overcome several limitations of terrestrial searches for dark matter, and advance challenging frontiers by orders of magnitude.

Speaker: Nirmal Raj (TRIUMF)

11:50 TBA

Speaker: Tongyan Lin (UCSD)

14:00 → 15:15 Short talks

14:00 TBA

Speaker: So Chigusa (University of Tokyo)

14:25 To B or not to B: Primordial magnetic fields from Weyl anomaly and Beyond

For more than twenty years, it has been argued that the Weyl anomaly of quantum electrodynamics sources cosmological magnetic fields in the early universe. If true, this would be a natural way to produce the seed magnetic fields of our universe within the Standard Model. In this talk, I will examine this long-standing claim and show that there is actually no production of coherent magnetic fields from the Weyl anomaly, irrespective of the number of massless charged particles in the early universe. I will also comment on other possibilities for magnetic field generation.

Speaker: Takeshi Kobayashi (Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University)

14:50 Primordial magnetic fields and 21-cm line observation

The primordial magnetic fields (PMFs) are expected to be generated in the early universe, and they are a possible origin of the present galactic magnetic fields. In this talk, we suggest a novel method to investigate the PMFs with 21-cm line observation. The recent observation of the 21-cm global absorption signal by EDGES suggests that the intergalactic medium (IGM) gas has been cooler than the cosmic microwave background around z~17. This result can provide a strong constraint on heating sources for the IGM gas at these redshifts. The PMFs are one of such heating sources due to the magnetohydrodynamic effects. By numerically solving the thermal evolution of the IGM gas with the PMFs, we find that the EDGES result gives a stringent limit on the PMFs as B_{1Mpc} less than 10^{-10} G.

Speaker: Teppei Minoda (Nagoya University)

15:45 → 16:35 Short talks

15:45 On the magnetogenesis and baryogenesis at the electroweak cross over

It has been found that baryon asymmetry of the Universe (BAU) can be generated without introducing any new physical ingredients beyond the Standard Model (SM) from the chiral asymmetry of the SM, if there exist helical hypermagnetic fields before the electroweak symmetry breaking. Then in order to explain the BAU, we need the physics beyond the SM to generate large-scale hypermagnetic fields. In this talk I will discuss the ways to generate such hypermagnetic fields suitable for baryogenesis.

Speaker: Kohei Kamada (RESCEU, U-Tokyo)

16:10 Baryogenesis from axion inflation

The coupling of an axion-like particle driving inflation to the Standard Model (SM) particle content through a Chern-Simons term generally sources a dual production of massless helical gauge fields and chiral fermions. We demonstrate that the interplay of these two components results in a highly predictive baryogenesis model, which requires no further ingredients beyond the Standard Model. If the helicity of the hyper magnetic field and the effective chemical potential of SM particles are large enough to avoid magnetic diffusion from the thermal plasma but small enough to delay the chiral plasma instability, then the non-vanishing helicity survives until the electroweak phase transition and sources a net baryon asymmetry which is in excellent agreement with the observed value. If any of these two conditions is violated, the final baryon asymmetry vanishes. The observed baryon asymmetry can be reproduced if the energy scale of inflation is around $H_\text{inf} \sim 10^{10}$-$10^{12}$ GeV with moderate dependence on inflation model parameters.

Speaker: Kyohei Mukaida (DESY)

17:05 → 17:55 Short talks

17:05 Curvature fluctuations from disorder during inflation

Although it is commonly assumed that the physics of inflation and the subsequent reheating epoch can be understood by means of simple effective field theories, there is no guarantee that this reductionist point of view is realized. In fact, some UV completions of inflation tend to involve many fields, with complicated interactions that can lead to significant elements of randomness in the dynamics. Nevertheless, in the limit of many fields/interactions, emergent universal properties may arise.

In this talk I will describe the effect of the repeated and non-adiabatic excitation of spectator fields on the primordial curvature power spectrum. In the absence of detailed information of the nature of spectator field interactions, we consider an ensemble of models with temporal locations and strengths of the interactions which are drawn from simple probabilistic distributions. I will show that the spectator fields evolve following geometric random walks, which on average source scale-dependent power spectra in spite of there being no preferred scale in the underlying model. Moreover, each member of the ensemble of spectra show rich structure with many features, susceptible of being probed by CMB and LSS observations. They can also have implications for primordial black hole formation and CMB spectral distortions.

Speaker: Marcos Garcia Garcia (IFT-UAM)

17:30 Big Bounce Baryogenesis

We explore the possibility of an Ekpyrotic phase induced by a fast rolling pseudoscalar field prior to a non-singular bounce harbouring a mechanism for Baryogenesis. Chern-Simons couplings to the Standard Model Hypercharge and Weak gauge fields enable the generation of a non-zero Chern-Simons number density during the contracting phase. The resulting baryon number produced is found to be consistent with observation for a range of couplings and high bounce scales. The gauge field production may also be a source of gravitational waves and provide the seeds of galactic magnetic fields.

Speaker: Neil Barrie (Kavli IPMU)

Wednesday 25 March

09:20 → 10:40 Invited talks

09:20 Future prospects of the 21cm cosmology

After reviewing basic aspects of 21cm brightness temperature observation from the epoch of reionization, we will discuss the 21cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in the spectra of high-redshift background radio sources in the cosmic reionization epoch. We will show that the 21cm forest observations are very sensitive to the mass of warm dark matter and ultra light dark matter, and it may be possible to probe the the mass range that may otherwise be difficult to access. We will also discuss a new idea of constraining cosmology beyond the cosmic variance limit using 21cm observations.

Speaker: Kiyotomo Ichiki (Nagoya University)

10:00 Probing the Primordial Universe with 21cm line

I discuss how one can probe the primordial Universe by using the neutral hydrogen 21 cm line, particularly focusing on primordial fluctuations. After briefly reviewing the physics of 21cm line, I discuss how the 21cm global signal, such as observed by EDGES, can probe small-scale primordial power spectrum. I also discuss the prospect of probing primordial non-Gaussianities with 21cm line. I argue that the 21 cm line would be a powerful probe of primordial fluctuations.

Speaker: Tomo Takahashi (Saga University)

11:10 → 12:30 Invited talks

11:10 An Independent Measurement of H0 from Lensed Quasars

Strong gravitational lens systems with time delays between the multiple images are a powerful probe of cosmology, particularly of the Hubble constant (H0) that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. The H0 Lenses In COSMOGRAIL’s Wellspring (H0LiCOW) project has measured H0 from lensed quasars using deep Hubble Space Telescope and AO imaging, precise time delay measurements from the COSMOGRAIL monitoring project, a measurement of the velocity dispersion of the lens galaxies, and a characterization of the mass distribution along the line of sight. Our latest results from a total of six lenses constrains H0 to be 73.3(-1.8,+1.7) km/s/Mpc for a flat Lambda CDM cosmology, which is a measurement to 2.4% precision. These results are consistent with independent determinations of H0 using type Ia supernovae calibrated by the distance ladder method, and are in 3.1-sigma tension with the results of Planck CMB measurements. Combined with the latest distance ladder results from the SH0ES project, we find a 5.3-sigma tension between Planck and late-Universe probes, hinting at possible new physics beyond the standard LCDM model and highlighting the importance of this independent probe.

Speaker: Kenneth Wong (Kavli IPMU)

11:50 A model of a dark matter from the Hubble tension and the core-cusp problem

In this talk, we propose a model for a dark matter (and dark sector) which is in complete decoupling with the Standard model sector. In an effort to identify DM's stability, mass and interaction type it does, we pay a special attention to two arguments that concern the Hubble tension and the core-cusp problem. Thereby, we aim at presenting a possibility of having a light decaying fermion DM which has both a theoretical and phenomenological appealing aspects.

Speaker: Gongjun Choi (Tsung-Dao Lee Institute, Shanghai)

14:00 → 15:15 Short talks

14:00 Higgs inflation, unitarity, and emergence of scalaron

The vanilla Higgs inflation introduces a large non-minimal coupling between the Ricci scalar and Higgs that causes the tree-level unitarity violation well below the Planck scale. After reviewing the unitarity issue of the Higgs inflation during and after inflation, we show that the unitarity can be restored by summing over vacuum polarization-type diagrams. The scattering amplitude develops a pole after the resummation, which we identify as the scalar component of the metric, or the scalaron. It suggests that the Higgs inflation is actually a multi-field inflation model, i.e. Higgs and the scalaron, and does not suffer from the unitarity problem.

Speaker: Yohei Ema (DESY)

14:25 Inflation and Preheating in the Mixed Higgs-R^2 Model

We consider the inflation and preheating process in a two-field model which consists of the R^2 term in the Starobinsky model and standard model Higgs field with non-minimal coupling. The inflation dynamics is found to be effectively single-filed like with large non-minimal coupling. The (p)reheating process presents different properties from those in single-field models. The violent behavior and the cutoff scale problem in the Higgs inflation are resolved by the R^2 term. More precisely, the cutoff scale is pushed up to Planck scale and the spiky effective mass found in the single-field Higgs inflation gets milder.

Speaker: Minxi He (RESCEU, UTokyo)

14:50 Entropy Production in Affine Inflation

Multiple scalar fields nonminimally interacting through pure affine gravity are considered to generate primordial perturbations during an inflationary phase. The couplings considered give rise to two distinct sources of entropy perturbations that may not be suppressed in the long wavelength limit. The first is merely induced by the presence of more than one scalar and arises even in the minimal coupling limit. The second source however is restricted to nonminimal interaction. Unlike the case of metric gravity, and due to the absence of anisotropic stresses, the second source disappears for single scalar, showing that nonminimal couplings become relevant to non-adiabatic perturbations only when more than one scalar field are considered. Hence the notion of adiabaticity is not affected by the transition to minimal coupling contrary to the metric gravity case where it becomes frame-dependent. Precise data that might be able to neatly track different sources of isocurvature modes, if any, must not only distinguish between different models of inflation but also determine the most viable approach to gravity which underlies the inflationary dynamics itself.

Speaker: Hemza Azri (Koç University, Istanbul)

15:45 → 16:35 Short talks

15:45 Solving the Hubble tension with Self Interacting Dirac Neutrino

In this talk I will show that a simple model of Dirac neutrinos that self-interact only through their right-handed components can naturally realize the self-interacting neutrino solution of the Hubble tension while evading all the cosmological or laboratory bounds.

Speaker: Jiaming Zheng (Shanghai Jiaotong University)

16:10 The effect of Hawking radiation on blackhole catalyzed phase transition

It has been discussed by Gregory et al. that small blackholes would catalyze vacuum phase transitions. We investigate such phase transition including the (inhomogeneous) thermal effect of Hawking radiation and calculate the bounce action numerically. I will show that the transition rate can be slightly suppressed by the thermal effect of Hawking radiation. I will also mention an application to the catalyzed phase transition associated with the Higgs metastability and conclude that the thermal effect may be negligible for the catalyst effect in the Higgs metastability, in contrast to the previous estimation without backreaction on spacetime metric. This means that if the Higgs metastability is true, the blackhole catalyst effect would be indeed catastrophic for our Universe.

Speaker: Takumi Hayashi (RESCEU Tokyo University)

17:05 → 17:55 Short talks

17:05 Grand Unification of a simple extension of Minimal Dark Matter and collider signatures

The Minimal Dark Matter (MDM) model suggested by Cirelli et al. is an extended model that introduces one SU (2) _L multiplet to the Standard Model so that the neutral component of the multiplet plays as the role of dark matter (DM). On the other hand, the stability of DM is not guaranteed because there is no mechanism to inhibit the DM decay process. We have built a model that makes DM automatically stable by embedding the MDM model into SO (10) grand unified theory. I will explain the model and report the results of studying the phenomenological limitations and predictions of the model.

Speaker: Kana Hayami (Ochanomizu University)

17:30 TBA

Speaker: Shih-Yen Tseng (The University of Tokyo)

Thursday 26 March

09:20 → 10:40 Invited talks

09:20 TBD (CMB observation - current status and future prospect)

Speaker: Akito Kusaka (The University of Tokyo; Lawrence Berkeley National Laboratory)

10:00 Dark matter search in extended dwarf spheroidal galaxies with CTA

The nature of dark matter (DM) is still a big mystery. Among the varieties of candidates, Weakly Interacting Massive Particle (WIMP) is one of the most promising ones. Gamma-ray observations of dwarf spheroidal galaxies (dSphs) by Fermi satellites put the strongest constraints at mDM~ < a few hundreds of GeV. In the near future, Cherenkov Telescope Array (CTA) starts its operations and expect to probe WIMP of mDM > ~O(1)TeV. Different from previous experiments, spatial distributions of DM in dSphs are resolved with CTA. In this talk, I explain the procedure to extract DM signals in gamma-ray observations and how the spatial extension of the dSph affects our accessibility to DM in future experiments.

Speaker: Nagisa Hiroshima (University of Toyama)

11:10 → 12:30 Invited talks

11:10 Current status and future prospects of gravitational-wave cosmology

Gravitational wave sources accompanied by electromagnetic counterparts
offer an independent standard siren measurement of the Hubble constant as
demonstrated following the discovery of the first neutron star merger, GW170817.
This measurement does not assume a cosmological model and is independent of
a cosmic distance ladder. I will talk about the first result of the Hubble constant
measurement using the gravitational-wave and electromagnetic signals from GW170817.
I'll also show how resolving the superluminal jet in a neutron star merger by the Very-long baseline
interferometry helps the measurement. I'll discuss the future prospects of gravitational-wave cosmology.

Speaker: Kenta Hotokezaka (Princeton Univ.; RESCEU)

11:50 TBA

Speaker: Kohta Murase (Penn State University)

14:00 → 15:15 Short talks

14:00 Observational constraint on interacting Tsallis holographic dark energy in logarithmic Brans-Dicke theory

In this paper, we investigate the dark energy phenomenon by studying the Tsallis holographic dark energy within the framework of Brans–Dicke (BD) scalar–tensor theory of gravity (Brans and Dicke in Phys. Rev. 124:925, 1961). In this context, we choose the BD scalar field ϕ as a logarithmic function of the average scale factor a(t) and Hubble horizon as the IR cutoff ( L=H^{−1} ). We reconstruct two cases of non-interacting and interacting fluid (dark sectors of cosmos) scenario. The physical behavior of the models are discussed with the help of graphical representation to explore the accelerated expansion of the universe. Moreover, the stability of the models are checked through squared sound speed v_s^2 . The well-known cosmological plane i.e., ω_{de}−ω′{de} is constructed for our models. We also include comparison of our findings of these dynamical parameters with observational constraints. It is also quite interesting to mention here that the results of deceleration, equation of state parameters and ω{de}−ω′_{de} plane coincide with the modern observational data.

Speaker: Sanjay Mandal (Birla Institute of Technology and Science-Pilani, Hyderabad Campus)

14:25 Stability of two fluid dark energy cosmological model with diagnostic analysis

In this paper, the stability analysis of an anisotropic dark energy cosmological model in a two fluid situations has been investigated. We have assumed that the dark energy pressure to be anisotropic in different spatial directions. several diagnostic analysis such as Om diagnostic, state finder analysis has also been incorporated and analysed. The results obtained are in accordance with the recent observational data.

Speaker: Bivudutta Mishra (BITS-Pilani, Hyderabad Campus)

15:45 → 16:35 Short talks

15:45 Aspects of Nonlinear Effect on Black Hole Superradiance

Under some conditions, light boson fields grow exponentially around a rotating black hole, called the superradiance instability. We discuss effects of nonlinear interactions of the boson on the instability. In particular, we focus on the effect of the particle production and show that the growth of the boson cloud may be saturated much before the black hole spin is extracted by the boson cloud, while the nonlinear interactions also induce the boson emission. For application, we revisit the superradiant instability of the standard model photon, axion and hidden photon.

Speaker: Hajime Fukuda (LBL)

16:10 Gravitational waves as a probe of small-scales: (Integrated) Sachs-Wolfe effect and spectral deformation

Gravitational waves (GWs) can be a sensitive probe of the early Universe dynamics. Once GWs are produced in the very early Universe (from whatever the source), their frequency and amplitude are affected by the density fluctuations on the way of their propagation. We point out that this effect, known as (Integrated) Sachs-Wolfe effect in CMB physics, appears as the deformation of the original GW spectrum. In other words, the detection of GWs from whatever early-Universe sources works not only as a probe to high-energy GW sources themselves, but also as a probe to density fluctuations in all the intermediate scales. In this presentation we discuss how we can quantify the spectral deformation of GWs, and also discuss how sensitive the detectors should be in order to see this effect. This presentation will be based on a work with V.Domcke and H.Rubira (to appear).

Speaker: Ryusuke Jinno (DESY)

17:05 → 17:55 Short talks

17:05 Probes of Dark Matter at LIGO and Beyond

We discuss probes of dark matter with chirping GWs. The example dark matter candidates include primordial black holes and axion-like particles. We first discuss lensing observables of primordial black holes: GW fringes and GRB lensing parallax. They finally allow probing a whole range of the PBH mass range with lensing. Then we discuss the disturbance due to dark matter waves in the environment of binary inspirals and in the galactic halo.

Speaker: Sunghoon Jung (Seoul National University)

17:30 Reconsideration of leptogenesis via circularly polarized gravitational waves

We revisit the gravitational leptogenesis scenario in which the lepton asymmetry is generated by circularly polarized gravitational waves during inflation, through the gravitational anomaly in the lepton number current. We consider a specific model in which the inflaton is coupled to gravity by the Chern-Simons term, and constrain the possible model parameter space by requiring the absence of ghost modes below the cutoff scale. We then evaluate the net baryon asymmetry in this model for typical reheating processes, which turned out to be insufficient to explain the observed baryon asymmetry of the Universe. We show that, however, with the kination scenario realized e.g. in the k- and G-inflation models, a sufficient baryon asymmetry can be generated within a feasible range of the model parameters.

Speaker: Jun'ya Kume (RESCEU, UTokyo)

18:45 → 20:45 Conference Dinner

Friday 27 March

09:20 → 10:40 Invited talks

09:20 TBA

Speaker: Yevgeny Stadnik (Kavli IPMU, University of Tokyo)

10:00 TBA

Speaker: Kenichi Saikawa (Kanazawa University)

11:10 → 12:30 Invited talks

11:10 TBA

Speaker: Koji Ishiwata (Kanazawa University)

11:50 Progress in understanding Dark Matter Sommerfeld-enhanced annihilation, bound-state formation and decay in the early Universe

Speaker: Tobias Binder (Kavli IPMU)

14:00 → 15:20 Invited talks

14:00 TBD

Speaker: Seong Chan Park (Yonsei University)

14:40 TBA

Speaker: Alejandro Ibarra (Technical University of Munich)