Interacting photon–baryon fluid, warm dark matter, and the first acoustic peak

The Reduced Relativistic Gas (RRG) model was introduced by A. Sakharov in 1965 for deriving the cosmic microwave background (CMB) spectrum. It was recently reinvented by some of us to achieve an interpolation between the radiation and dust epochs in the evolution of the Universe. This model circumvents the complicated structure of the Boltzmann–Einstein system of equations and admits a transparent description of warm-dark-matter effects. It is extended here to include, on a phenomenological basis, an out-of-equilibrium interaction between radiation and baryons which is supposed to account for relevant aspects of pre-recombination physics in a simplified manner. Furthermore, we use the tight-coupling approximation to explore the influence of both this interaction and of the RRG warmness parameter on the anisotropy spectrum of the CMB. The predictions of the model are very similar to those of the Λ CDM model if both the interaction and the dark-matter warmness parameters are of the order of 10-4 or smaller. As far as the warmness parameter is concerned, this is in good agreement with previous estimations on the basis of results from structure formation

Aspects of the cosmological “coincidence problem”

The observational fact that the present values of the densities of dark energy and dark matter are of the same order of magnitude, ρde0/ρdm0∼O(1) , seems to indicate that we are currently living in a very special period of the cosmic history. Within the standard model, a density ratio of the order of one just at the present epoch can be seen as coincidental since it requires very special initial conditions in the early Universe. The corresponding “why now” question constitutes the cosmological “coincidence problem”. According to the standard model the equality ρde=ρdm took place “recently” at a redshift z≈0.55 . The meaning of “recently” is, however, parameter dependent. In terms of the cosmic time the situation looks different. We discuss several aspects of the “coincidence problem”, also in its relation to the cosmological constant problem, to issues of structure formation and to cosmic age considerations

Orbit based procedure for doublets of scalar fields and the emergence of triple kinks and other defects

In this work we offer an approach to enlarge the number of exactly solvable models with two real scalar fields in ( 1+1 )D. We build some new two-field models, and obtain their exact orbits and exact or numerical field configurations. It is noteworthy that a model presenting triple-kinks and double-flat-top lumps is among those new models

Topological vertex, string amplitudes and spectral functions of hyperbolic geometry

We discuss the homological aspects of the connection between quantum string generating function and the formal power series associated to the dimensions of chains and homologies of suitable Lie algebras. Our analysis can be considered as a new straightforward application of the machinery of modular forms and spectral functions (with values in the congruence subgroup of SL(2,Z) ) to the partition functions of Lagrangian branes, refined vertex and open string partition functions, represented by means of formal power series that encode Lie algebra properties. The common feature in our examples lies in the modular properties of the characters of certain representations of the pertinent affine Lie algebras and in the role of Selberg-type spectral functions of a hyperbolic three-geometry associated with q -series in the computation of the string amplitudes

Cosmological solutions from induced matter model applied to 5D f(R,T) gravity and the shrinking of the extra coordinate

In this work, I present exact cosmological solutions from Wesson’s induced matter model applied to a general 5D metric in f(R,T) theory of gravity. The non-conservation of the energy-momentum tensor, predicted by f(R,T) theory, allows the derivation of a relation that describes the time evolution of the extra coordinate, revealing its compactification. It is shown that such a compactification could induce the effects of an accelerated expansion in the observable universe

Aspects of semilocal BPS vortex in systems with Lorentz symmetry breaking

The existence is shown of a static self-dual semilocal vortex configuration for the Maxwell–Higgs system with a Lorentz-violating CPT-even term. The dependence of the vorticity upper limit on the Lorentz-symmetry-breaking term is also investigated

Black holes in AdS/BCFT and fluid/gravity correspondence

A proposal to describe gravity duals of conformal theories with boundaries (AdS/BCFT correspondence) was put forward by Takayanagi few years ago. However interesting solutions describing field theories at finite temperature and charge density are still lacking. In this paper we describe a class of theories with boundary, which admit black hole type gravity solutions. The theories are specified by stress-energy tensors that reside on the extensions of the boundary to the bulk. From this perspective AdS/BCFT appears analogous to the fluid/gravity correspondence. Among the class of the boundary extensions there is a special (integrable) one, for which the stress-energy tensor is isotropic. We discuss features of that special solution as well as its thermodynamic properties

Polytropic equation of state and primordial quantum fluctuations

We study the primordial Universe in a cosmological model where inflation is driven by a fluid with a polytropic equation of state p=αρ+kρ1+1/n . We calculate the dynamics of the scalar factor and build a Universe with constant density at the origin. We also find the equivalent scalar field that could create such an equation of state and calculate the corresponding slow-roll parameters. We calculate the scalar perturbations, the scalar power spectrum, and the spectral index

Anomalous gauge couplings from composite Higgs and warped extra dimensions

We examine trilinear and quartic anomalous gauge couplings (AGCs) generated in composite Higgs models and models with warped extra dimensions. We first revisit the SU(2) L × U(1) Y effective Lagrangian and derive the charged and two-photon neutral AGCs. We derive the general perturbative contributions to the pure field-strength operators from spin 0, $\frac{1}{2}$ , 1 resonances by means of the heat kernel method. In the composite Higgs framework, we derive the pattern of expected deviations from typical SO( N ) embeddings of the light composite top partner. We then study a generic warped extra dimension framework with AdS 5 background, recasting in few parameters the features of models relevant for AGCs. We also present a detailed study of the latest bounds from electroweak and Higgs precision observables, with and without brane kinetic terms. For vanishing brane kinetic terms, we find that the S and T parameters exclude KK gauge modes of the RS custodial [non-custodial] scenario below 7 . 7 [14 . 7] TeV, for a brane Higgs and below 6 . 6 [8 . 1] TeV for a Pseudo Nambu-Goldstone Higgs, at 95% CL. These constraints can be relaxed in presence of brane kinetic terms. The leading AGCs are probing the KK gravitons and the KK modes of bulk gauge fields in parts of the parameter space. In these scenarios, the future CMS and ATLAS forward proton detectors could be sensitive to the effect of KK gravitons in the multi-TeV mass range

Field theoretic description of electromagnetic boundaries

In a previous work we formulated a model of semitransparent dielectric surfaces, coupled to the electromagnetic field by means of an effective potential. Here we consider a setup with two dissimilar mirrors, and we compute exactly the correction undergone by the photon propagator due to the presence of both plates. It turns out that this new propagator is continuous all over the space and, in the appropriate limit, coincides with the one used to describe the Casimir effect between perfect conductors. The amended Green function is then used to calculate the Casimir energy between the uniaxial dielectric surfaces described by the model, and a numerical analysis is carried out to highlight the peculiar behavior of the interaction between the mirrors