Available talk files are linked to the speaker names in the timetable.

12/12 (Mon) 12/13 (Tue) 12/14 (Wed) 12/15 (Thu)

Morning Session

10:00 - 12:30


Asimina Arvanitaki

Andreas Ringwald

Jonah Kanner
Coffee Break Coffee Break Coffee Break
Carlos Herdeiro Yoshizumi Inoue Hirotaka Yoshino

Registration 12:45- 13:20

Lunch Lunch Lunch

Afternoon Session I
13:30 - 15:30

Ralph Blumenhagen

Joseph Conlon

Jens Chluba

Takahiro Tanaka
Yuko Urakawa Kazunori Kohri Ippei Obata Naoya Kitajima
Tatsuo Kobayashi Fuminobu Takahashi Arata Aoki Closing
  Coffee Break Coffee Break Coffee Break (group photo)  

Afternoon Session II
16:00 - 18:00

Natsumi Nagata D. J. E. Marsh Yuto Minami  
Osamu Seto Kazunori Nakayama  
Toyokazu Sekiguchi Hajime Otsuka  
18:00 - 20:00    


Last Update: Dec. 26, 2016


To see the program pdf file, click here.

Invited Talks (50 min + 10 min)

Asimina Arvanitaki (Perimeter Inst)

"The highs and lows of the QCD axion"

The highs and lows of the QCD axion The QCD axion has been proposed more than 30 years ago to explain the smallness of the neutron's electric dipole moment. It is an excellent Dark Matter candidate and the search for it has been ongoing ever since its conception. In my talk I will describe two experiments that will explore complementary parts of the axion's parameter space. When the axion's Compton wavelength is tens of microns up to several centimeters, it can be detected through the monopole-dipole and dipole-dipole interaction it mediates in matter. In our ARIADNE proposal, the tiny effect of this interaction can be measured using polarized He-3. When the axion's Compton wavelength is larger than a kilometer, it matches the size of astrophysical black holes and its presence can be diagnosed through the superradiance effect that causes BHs to spin down. During this process, a cloud of axions forms a gravitational atom around the BH nucleus. Monochromatic gravitational waves produced by atomic transitions in this cloud turn BHs into astrophysical beacons that are well within the reach of Advanced LIGO experiment; after the discovery of gravitational waves, Advanced LIGO may also diagnose the existence of a new particle.

Ralph Blumenhagen (MPIfP)

"String Moduli Stabilization and Large Field Inflation (tentative)"

To realize models of primordial inflation with an observable tensor-to-scalar ratio the inflaton needs to role over a trans-Plankian distance in field space. A proper treatment requires a discussion in a UV-complete theory as string theory. In this talk, attempts to realize such concrete models in string theory model building are reviewed. These are closely related to the issue of moduli stabilisation. Special emphasis is put on so-called models of F-term axion monodromy inflation.

Joseph Conlon (Oxford U)

"Searching for Axion-Like Particles in Active Galactic Nuclei"

If they exist, axion-like particles can lead to oscillatory features in the spectra of Active Galactic Nuclei. I describe observational searches for these features using X-ray telescopes and evidence for such features in the spectrum of NGC1275, the central AGN of the Perseus cluster.

Jens Chluba (U of Manchester)

"What CMB spectral distortions can teach us about early-universe and particle physics"

Since the measurements with COBE/FIRAS in the mid-90's we know that the CMB spectrum is extremely close to a perfect blackbody. There are, however, a number of processes in the early Universe that should create spectral distortions at a level within reach of present day technology. I will give an overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open up an unexplored new window to early-universe and particle physics, with possible non-standard surprises and several guaranteed signals awaiting us. I will highlight the complementarity of the distortion signals and the CMB anisotropies, illustrating how future distortions measurements will shed new light on different inflation models.

Carlos A. R. Herdeiro (U Aveiro)

"Kerr black holes with scalar or Proca hair"

Over the last two years it has been found that new classes of asymptotically flat black hole solutions, regular on and outside the event horizon, bifurcating from the vacuum Kerr solution, exist in General Relativity, with simple matter contents that obey all energy conditions, namely Kerr black holes with scalar hair [1] and Proca hair [2]. In this talk I will review the general mechanism that allows these solutions to exist, intimately connected to superradiance, how these solutions circumvent well known no-hair theorems and some of their phenomenology which can be considerably distinct from that of Kerr [3,4].

[1] Kerr black holes with scalar hair
Carlos A. R. Herdeiro, Eugen Radu
Phys.Rev.Lett. 112 (2014) 221101
[2] Kerr black holes with Proca hair
Carlos Herdeiro, Eugen Radu, Helgi Runarsson
Class.Quant.Grav. 33 (2016) no.15, 154001
[3] Construction and physical properties of Kerr black holes with scalar hair
Carlos Herdeiro, Eugen Radu
Class.Quant.Grav. 32 (2015) 14, 144001
[4] Shadows of Kerr black holes with scalar hair
Pedro V. P. Cunha, Carlos A. R. Herdeiro, Eugen Radu, Helgi F. Runarsson
Phys.Rev.Lett. 115 (2015) 21, 211102

Yoshizumi Inoue (U Tokyo)

"Hidden photon search experiments at Tokyo"

We will report on a couple of experiments carried out at the University of Tokyo aiming at the direct detection of hidden photon dark matter utilizing a faint photon emission from reflective surfaces. In one experiment, we used a 50cm-concave mirror aiming at the detection of hidden photons with a mass of the visible photon energy. In the other, we combined a commercially available 2.2-m parabolic antenna and a plane reflector aiming at the hidden photons with a mass of 50 ueV. In both experments, we found no evidence for the hidden photon dark matter.

Jonah Kanner ( Caltech)

"Searching for new sources of gravitational waves"

Recently Advanced LIGO began taking data, allowing for the first direct observation of gravitational waves. So far, all of the observed signals are consistent with originating from mergers of binary black holes. With this new class of instruments, it is possible that we will someday also observe signals from other origins. In this talk, I will describe how we search the gravitational wave data broadly, seeking both transient and continuous signals from wide classes of possible sources.

David J. E. Marsh (King’s College London)

"Axion Cosmology and the Lightest DM Candidate"

Due to the exponetial sensitivity to the cycle volumes, string axions can be extremely light. If the axion is lighter than the Hubble scale at BBN, and the decay constant is sufficiently large, then there are interesting, and potentially observable, effects on the acoustic peaks and graitational lensing of the CMB power spectrum, and on galaxy formation. These effects can be used to search for axions in cosmological and astrophysical data. Current constraints from Planck limit axions over eight orders of magnitude in mass to have sub-Planckian decay constants. Upcoming "CMB Stage IV" lensing data will probe ten ordes of magnitude in mass and could detect axion DM with GUT scale decay constants at high statistical significance. This represents sub-percent level tests of the single-component standard cold DM model. Constraints from high redshift structure formation with axion DM place the current best lower bound on DM particle mass, m>1e-22 eV, which may be relevant to certain issues with the standard cold DM model. This lower bound could be improved by up to four orers of magnitude using futurisitic 21cm surveys.Given time, I will discuss the ideas and challenges to detect axion DM in this mass window.

Yuto Minami (KEK)

"LiteBIRD: A future satellite mission on CMB polarization"

LiteBIRD is a next-generation scientific satellite mission aiming to measure the polarization of the Cosmic Microwave Background (CMB) radiation at unprecedented sensitivity. The B-mode polarization of the CMB carries the imprint of primordial gravitational waves, and its precise measurement with large angular scale would provide a powerful probe of the inflation mechanism. In this talk, the overview of the CMB measurement and the goal of the LiteBIRD will be given.

Natsumi Nagata (U Tokyo)

"A supersymmetric two-field relaxion model"

We discuss a supersymmetric version of a two-field relaxion model that naturalizes supersymmetric models with high SUSY-breaking. This exploits a relaxion mechanism that does not depend on QCD dynamics and where the relaxion potential barrier height is controlled by a second axion-like field. During the cosmological evolution, the relaxion rolls down with a nonzero value that breaks supersymmetry and scans the soft supersymmetric mass terms. Electroweak symmetry is broken after the soft masses become of order the supersymmetric Higgs mass term and causes the relaxion to stop rolling. This can explain the tuning in supersymmetric models, while preserving the QCD axion solution to the strong CP problem. We will also consider possible inflation models compatible with this framework.

Andreas Ringwald (DESY)

"The Quest for the Axion and Axion-Like Particles"

Many theoretically well-motivated extensions of the standard model of particle physics predict the existence of very weakly interacting ultralight particles, such as the axion and similar Nambu-Goldstone bosons. They may constitute the mysterious dark matter n the universe and solve some puzzles in stellar and high-energy astrophysics. There are new, relatively small experiments around the globe, which started to hunt for these elusive particles and complement the search for physics beyond the Standard Model at the Large Hadron Collider.

Takahiro Tanaka (Kyoto U)

"Testing gravity theory by gravitational waves"

Recently, various modified gravity theories have been proposed motivated by constructing consistent cosmological models. Also,consistent modification of gravity has been studied for many years to provide well-motivated tests of general relativity. We would like to discuss the constraints on possible modification of gravity that would be obtained from the future observations of gravitational waves.

Hirotaka Yoshino (Osaka City U)

"Axion Bosenova and Gravitational Waves"

String theories predict the existence of scalar fields with ultralight mass (string axion field). In this talk, I explain our studies on phenomena caused by string axions around a rotating black hole. By developing a highly accurate numerical code, we followed the growth of axion field by the superradiant instability and the subsequent violent phenomena ''bosenova'' caused by nonlinear self-interaction. Gravitational waves emitted from this system are also simulated. We discuss whether such gravitational waves can be observed by ground- and space-based detectors.

Contributed Talks (25 min + 5 min)

Arata Aoki (Kobe U)

"Probing ultralight axion dark matter with gravitational-wave detectors"

The ultralight axion with mass around 10^{-22} eV is a candidate of dark matter. A peculiar feature of the ultralight axion is oscillating pressure in time, which produces an oscillation of gravitational potentials. The oscillating potentials can, in principle, be detected by gravitational-wave detectors. I will also discuss the possible enhancement of the detector signal in modified gravity theories explaining dark energy.

Naoya Kitajima (APCTP)

"Topological Defects in Aligned Axion Models"

We study the formation and evolution of topological defects in an aligned axion model with multiple Peccei-Quinn scalars, where the QCD axion is realized by a certain combination of the axions with decay constants much smaller than the conventional Peccei-Quinn breaking scale. The string-wall system collapses during the QCD phase transition, producing a significant amount of gravitational waves in the nano-Hz range at present.

Tatsuo Kobayashi (Hokkaido U)

"Small field axion inflation"

We study small field axion inflation within the framework of superstring theory. We discuss generic aspects on observables and thermal history.

Kazunori Kohri (KEK)

"Recent IR background observations and Axion-photon conversions"

The CIBER experiment is now preparing for their data release of the Extragalactic IR Background Light, which is a first measurement of the diffuse background spectrum at 0.8 -- 1.7 micro meters. The amount of the IR background at around those wavelengths is sensitive to an opaqueness of the TeV gamma-rays emitted from distant sources such as blazars and so on. Through scatterings of TeV gamma-rays off the IR background photons, the TeV gamma-rays are partly absorbed, which can be measured by gamma-ray observations such as Fermi or H.E.S.S. By checking consistencies between the TeV gamma-rays and the IR background, we can obtain various information for physical processes. In this talk I discuss a possible interrelation for features of the observational data in terms of Axion-Like Particles (ALPs) which induces photon-axion conversions during the propagation of the TeV gamma-rays from the distant sources.

Kazunori Nakayama (U Tokyo)

"Moduli-assisted electroweak vacuum"

It is known that the potential of standard model Higgs field is unbounded from below and it may lead to a serious instability during/after inflation. We propose a simple solution to the problem of vacuum instability during/after inflation. If there is a hidden-sector moduli field which has Planck-suppressed interactions with the standard model fields, the Higgs quartic coupling in the early universe naturally takes a different value from the present one and it may ensure the stability of electroweak vacuum during/after inflation.

Ippei Obata (Kyoto U)

"Chiral primordial blue tensor spectra from the axion-gauge coupling"

The inflationary universe predicts vacuum fluctuations of space-time, called primordial gravitational waves, whose spectra have slightly red-tilted and parity-symmetric features. Intriguingly, however, it is known that the axion-gauge coupling, motivated by string theory, could occur the particle production of gauge fields during inflation and provide the parity-violated blue tensor spectrum testable in future gravitational wave experiments, while no such a parity-violated primordial signal has been detected through recent CMB observations. In this talk, we suggests the new mechanism of providing blue tensor spectra sourced by gauge fields coupled to axions, surprisingly whose amplitudes are almost parity-conserved but slightly parity-violated! We expect that this blue tensor spectra with little chirality becomes the new window to the axion phenomenology in the early universe.

Hajime Otsuka (Waseda U)

"Affleck-Dine baryogenesis on an axion background"

In the string axion inflation, the axion inflaton naturally couples to the Affleck-Dine field through the Yukawa coupling. On this axion background, we investigate the Affleck-Dine baryogenesis. Analytical and numerical estimations show that the baryon asymmetry is enough produced even without soft SUSY breaking A-term.

Toyokazu Sekiguchi (CTPU, I. Basic Science)

"Cosmological relaxation with high reheating temperature"

We propose a new scenario of cosmological relaxation compatible with reheating temperature higher than the electroweak scale. Cosmological relaxation is a new solution to the hierarchy problem which is recently proposed. However, the barrier potential, which stops the relaxion to realize the correct electroweak scale, vanishes at high temperature above the electroweak scale. Therefore, the conventional scenario is not compatible with high reheating temperature, which is often requested in other cosmological context, e.g. baryogenesis. We tackle this issue by introducing an anomalous coupling of the relaxion with a hidden U(1) gauge field. In this case, motion of the relaxion explosively produces the coupled gauge field via tachyonic instability and undergoes significant friction as backreaction. We show that this efficiently suppresses the excursion of relaxion after reheating. In addition, the introduction of the coupling to a hidden gauge field can mitigate many constraints exist in the conventional scenario from astrophysics and terrestrial experiments. Instead, the amount of produced gauge bosons is subject of cosmological constraints. We show the viable parameter space for our scenario.

Osamu Seto (Hokkaido U)

"Parameter range of relaxion"

We investigate cosmological constraints on the original relaxion scenario proposed by Graham, Kaplan and Rajendran. We derive the cosmologically consistent ranges of the mass and a coupling of the relaxion therein. We also find that a strong correlation between Hubble parameter at the relaxion stabilization and the scale Λ of non-QCD strong dynamics.

Fuminobu Takahashi (Tohoku U)

"Hidden photon and GUT"

I will discuss a gauge coupling unification in the SM with a hidden photon, which has a large kinetic mixing with hyper charge. I will also briefly mention its implications for mini-charged dark matter.

Yuko Urakawa (Nagoya U)

"Modular invariant inflation"

Modular invariance is a striking symmetry in string theory, which may keep stringy corrections under control. In this talk, we investigate a phenomenological consequence of the modular invariance, assuming that this symmetry is preserved as well as in a four dimensional (4D) low energy effective field theory. As a concrete setup, we consider a modulus field T whose contribution in the 4D effective field theory remains invariant under the modular transformation and study inflation drived by T. The modular invariance restricts a possible form of the scalar potenntial. As a result, large field models of inflation are hardly realized. Meanwhile, a small field model of inflation can be still accomodated in this restricted setup. We also report the consistency of this model with the CMB observations.




    This workshop is supported by the Yukawa Institute for Theoretical Physics and the JSPS Grant-in-Aid for Scientific Research (A) 26247042
    "Quest for the Ultimate Theory in terms of rich cosmophysical phenomena caused by fields and particles in the hidden sector".