Yusuke Mikura

Abstract We investigate the UV-completion of the Higgs inflation in the metric and the Palatini formalisms. It is known that the cutoff scales for the perturbative unitarity of these inflation models become much smaller than the Planck scale to be consistent with observations. Expecting that the low cutoff scales originate in the curvature of a field-space spanned by the Higgs fields, we consider embedding the curved field-space into a higher dimensional flat space and apply this procedure to th

\n\nSystematic understanding for classes of inflationary models is investigated from the viewpoint of the local conformal symmetry and the slightly broken global symmetry in the framework of the metric-affine geometry. In the metric-affine geometry, which is a generalisation of the Riemannian one adopted in the ordinary General Relativity, the affine connection is an independent variable of the metric rather than being given, e.g., by the Levi-Civita connection as its function. Thanks to this in

We motivate a minimal realization of slow-roll $k$-inflation by incorporating the local conformal symmetry and the broken global SO(1,1) symmetry in the metric-affine geometry. With use of the metric-affine geometry where both the metric and the affine connection are treated as independent variables, the local conformal symmetry can be preserved in each term of the Lagrangian and thus higher derivatives of scalar fields can be easily added in a conformally invariant way. Predictions of this mini

We consider antisymmetric metric-affine theories of gravity with a Lagrangian containing the most general terms up to dimension four and search for theories that are ghost- and tachyon-free when expanded around flat space. We find new examples that propagate only the graviton and one other massive degree of freedom of spin zero, one, or two. These models require terms of the form $(\ensuremath{\nabla}T{)}^{2}$ in the Lagrangian, that have been largely ignored in the literature.

Abstract We propose an extension of the Higgs inflation to the hybrid metric-Palatini gravity, where we introduce non-minimal couplings between Higgs and both the metric-type and the Palatini-type Ricci scalars. We study the inflationary phenomenology of our model and find that slow-roll inflation can be realized in the large-field regime, giving the observationally favored predictions. In particular, the scalar spectral index exhibits an attractor behavior to n s ∼ 0.964, while the tensor-to-sc

Abstract We investigate symmetric metric-affine theories of gravity with a Lagrangian containing all operators of dimension up to four that are relevant to free propagation in flat space. Complementing recent work in the antisymmetric case, we derive the conditions for the existence of a single massive particle with good properties, in addition to the graviton.

We investigate symmetric Metric-Affine Theories of Gravity with a Lagrangian containing all operators of dimension up to four that are relevant to free propagation in flat space. Complementing recent work in the antisymmetric case, we derive the conditions for the existence of a single massive particle with good properties, in addition to the graviton.

Abstract Towards a classification of UV completable Higgs inflation in the framework of parity-even metric-affine gravity, we investigate the particle spectrum of a deformed theory in the large- N limit. In a simple Higgs inflation model in metric-affine gravity, it is known that its UV cutoff is much smaller than the Planck scale. While it calls for UV completion, a concrete example has not yet been found, even with the large- N limit known as a successful technique to complete an original Higg

We consider antisymmetric Metric-Affine Theories of Gravity with a Lagrangian containing the most general terms up to dimension four and search for theories that are ghost- and tachyon-free when expanded around flat space. We find new examples that propagate only the graviton and one other massive degree of freedom of spin zero, one or two. These models require terms of the form $(\nabla T)^2$ in the Lagrangian, that have been largely ignored in the literature.

Towards a classification of UV completable Higgs inflation in the framework of parity-even metric-affine gravity, we investigate the particle spectrum of a deformed theory in the large-$N$ limit. In a simple Higgs inflation model in metric-affine gravity, it is known that its UV cutoff is much smaller than the Planck scale. While it calls for UV completion, a concrete example has not yet been found, even with the large-$N$ limit known as a successful technique to complete an original Higgs infla

Gravitational waves (GWs) distort galaxy shapes through the tidal effect, offering a novel avenue to probe the nature of gravity. In this paper, we investigate how extra GW polarizations beyond those predicted by general relativity imprint observable signatures on galaxy shapes. Since galaxy shapes are measured as two-dimensional images projected onto the celestial sphere, we present three-dimensional statistical quantities of the projected tidal tensor sourced by the tensor perturbation. We sho