Maxim V. Libanov

Firmly established in astrophysical observations, dark matter evades direct detection in experiments. Axions and axionlike particles are among the leading dark-matter candidates, and numerous attempts to detect them in laboratories have been performed. Here, we propose to advance these efforts substantially, extending the sensitivity for dark-matter axions in the mass range ( 38 – 54 ) μ eV down to the axion-photon couplings g a γ γ ≲ ( 10 − 14 − 10 − 15 ) GeV − 1 , motivated by generic models of quantum chromodynamics axion. Single-photon detectors operating at ultralow temperatures are key elements of the experiment. The projected sensitivity will be reached in one year of data taking with magnetic field of (1–10) T, making Cosmological Axion Sarov Haloscope (CASH) the most sensitive haloscope in this mass range.

In this paper, we propose an approach based on the theory of an axiomatic S matrix and partially switching on an interaction, which is extremely suitable for describing the phenomenon of oscillations within the framework of quantum field theory. We discuss the relation of the proposed approach with other approaches based on considering of wave packets as asymptotic states or introducing of “distance- or time-dependent propagators”.

Motivated by holographic models of a (pseudo)conformal Universe, we carry out a complete analysis of linearized metric perturbations in the time-dependent two-brane setup of the Lykken-Randall type. We present the equations of motion for the scalar, vector and tensor perturbations and identify light modes in the spectrum, which are scalar radion and transverse-traceless graviton. We show that there are no other modes in the discrete part of the spectrum. We pay special attention to properties of light modes and show, in particular, that the radion has red power spectrum at late times, as anticipated on holographic grounds. Unlike the graviton, the radion survives in the single-brane limit, when one of the branes is sent to the adS boundary. These properties imply that potentially observable features characteristic of the 4d (pseudo)conformal cosmology, such as statistical anisotropy and specific shapes of non-Gaussianity, are inherent also in holographic conformal models as well as in brane world inflation.

Approximate de Sitter symmetry of inflating Universe is responsible for the approximate flatness of the power spectrum of scalar perturbations. However, this is not the only option. Another symmetry which can explain nearly scale-invariant power spectrum is conformal invariance. We give a short review of models based on conformal symmetry which lead to the scale-invariant spectrum of the scalar perturbations. We discuss also potentially observable features of these models.Comment: Mini-review, prepared for JETP Letters; 11 pages, 3 figure

Approximate de Sitter symmetry of inflating Universe is responsible for the approximate flatness of the power spectrum of scalar perturbations. However, this is not the only option. Another symmetry which can explain nearly scale-invariant power spectrum is conformal invariance. We give a short review of models based on conformal symmetry which lead to the scale-invariant spectrum of the scalar perturbations. We discuss also potentially observable features of these models.

We point out that the (pseudo)conformal universe scenario may be realized as the decay of a conformally invariant, metastable vacuum, which proceeds via spontaneous nucleation and subsequent growth of a bubble of a putative new phase. We study perturbations about the bubble and show that their leading late-time properties coincide with those inherent in the original models with homogeneously rolling backgrounds. In particular, the perturbations of a spectator dimension-zero field have a flat power spectrum.