The existence of light particles with spin during inflation is prohibited by the Higuchi bound. This conclusion can be evaded if one considers states with a sizeable coupling with the inflaton foliation, since this breaks the de Sitter isometries. The action for these states can be constructed within the Effective Field Theory of Inflation, or using a CCWZ procedure. Light particles with spin...

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...

I will talk about the Dirac procedure for constrained systems applied to the Arnowitt-Deser-Misner formalism linearized around the Friedmann-Lemaitre universe. I will employ some basic concepts such as Dirac observables, Dirac brackets, gauge-fixing conditions, reduced phase space, physical Hamiltonian and physical dynamics, and the canonical isomorphism between different gauge-fixed surfaces....

Identification of dark matter has been an outstanding problem in

physics for decades, and axion (or axion like partciles) is its

candidate with great motivations. A number of observations and experiments have tried to detect axion by using the axion-photon conversion by assuming the axion is coupled to photon, while no signal yet to be found. In this talk, I will discuss new techniques to...

Abstract: Gravitational wave (GW) astronomy provides us a unique chance to probe invisible matter in the universe. In this talk we introduce several ways of probing dark ambient matter of compact binaries through GWs. We first present some analytical understanding of the distribution of binaries' orbital parameters and its relation to binaries' formation channels. Then, we describe how the...

The rapid expansion of inflationary universe amplifies microscopic linear quantum fluctuations of non-conformally coupled fields such as the minimally coupled massless scalar, and generates large superhorizon correlators. On the other hand, conformally coupled fields such as the photon are insensitive to the expansion itself. However, if the photon couples to the complex scalar the effect of...

In this talk, we construct Lorentz-invariant massive spin-2

theories in a flat space-time. Starting from the most general action of a massive spin-2 field whose Lagrangian contains up to quadratic in first derivatives of a field, we investigate new possibilities by using the Hamiltonian analysis. By imposing degeneracy of the kinetic matrix and the existence of subsequent constraints, we...

Probably not. I will introduce some different gravity theories which are as good as GR in the sense that all of constraints are first class and therefore a graviton has only 2 polarisations and the structure of the theory at low energies is thus expected to be stable against quantum corrections.

In arXiv:1811.09547 we introduced an interesting new Weyl-invariant and generally-covariant vector-tensor theory with higher derivatives. This theory can be induced by extending the mimetic construction to vector fields of conformal weight four. We demonstrated that in gauge-invariant variables this novel theory reduces to the Henneaux–Teitelboim description of the unimodular gravity. Hence,...

We investigate the spontaneous breaking of Weyl conformal geometry to Einstein gravity in the presence/absence of matter with non-minimal couplings and possible applications to model building beyond SM.

The modern theory of ghost-free massive gravity hinges upon the notion of a square root of a matrix. This is non-trivial and not unique. It makes the standard perturbation theory in terms of matrices problematic, and in some cases even impossible. I will describe the mathematics behind these issues, and also discuss a method of dealing with perturbation theory around a given solution in terms...

What is the maximum possible strength of a first-order electroweak phase transition and the resulting gravitational wave signal? While naively one might expect that supercooling could increase the strength of the transition to very high values, for strong supercooling the Universe is no longer radiation-dominated and the vacuum energy of the unstable minimum of the potential dominates the...

The information loss problem in black hole physics is a very important but unresolved problem. I will review the issue including the recent discussion with the firewall controversy. Instead of the firewall conjecture or other candidates of resolutions, I will suggest that the Euclidean path integral sheds some lights to the problem.

I will review the problem of the acceleration of the expansion of the universe at late times and discuss how models of modifications of gravity can provide an alternative mechanism to the cosmological constant. I will discuss the space of models, how to best think about the generic effects these models have on structure formation and therefore how they can be constrained through observations....