Signature of the interaction between dark energy and dark matter in galaxy clusters

We investigate the influence of an interaction between dark energy and dark matter upon the dynamics of galaxy clusters. We obtain the general Layser–Irvine equation in the presence of interactions, and find how, in that case, the virial theorem stands corrected. Using optical, X-ray and weak lensing data from 33 relaxed galaxy clusters, we put constraints on the strength of the coupling between the dark sectors. Available data suggests that this coupling is small but positive, indicating that dark energy might be decaying into dark matter. Systematic effects between the several mass estimates, however, should be better known, before definitive conclusions on the magnitude and significance of this coupling could be established.     

Domain wall universe in the Einstein–Born–Infeld theory

In this Letter, we discuss the dynamics of a domain wall universe embedded into the charged black hole spacetime of the Einstein–Born–Infeld (EBI) theory. There are four kinds of possible spacetime structures, i.e., those with no horizon, the extremal one, those with two horizons (as the Reissner–Nordström black hole), and those with a single horizon (as the Schwarzshild black hole). We derive the effective cosmological equations on the wall. In contrast to the previous works, we take the contribution of the electrostatic energy on the wall into account. By examining the properties of the effective potential, we find that a bounce can always happen outside the (outer) horizon. For larger masses of the black hole, the height of the barrier between the horizon and bouncing point in the effective potential becomes smaller, leading to longer time scales of bouncing process. These results are compared with those in the previous works.     

A dark radiation era prior to the inflationary phase

A cosmological model dominated at the beginning by a dark radiation followed by a period of inflation is presented. This model is based on a Randall–Sundrum II type brane-world. Current observational data are used to fix the parameters associated to the dark radiation.     

Exorcising w < −1

We show that the combined dimming of Type Ia supernovae induced by both a cosmological constant and the conversion of photons into axions in extra-galactic magnetic fields can impersonate dark energy with an equation of state w < −1. An observer unaware of the presence of photon-axion conversion would interpret the additional dimming as cosmic acceleration faster than that induced by a cosmological constant alone. We find that this mechanism can mimic equations of state as negative as w ? −1.5. Our model does not have any ghosts, phantoms, and the like. It is fully consistent with the conventional effective field theory in curved space, and all existing observational constraints on the axions are obeyed.     

The role of domain wall junctions in Carter's pentahedral model

The role of domain wall junctions in Carter's pentahedral model is investigated both analytically and numerically. We perform, for the first time, field theory simulations of such model with various initial conditions. We confirm that there are very specific realizations of Carter's model corresponding to square lattice configurations with X-type junctions which could be stable. However, we show that more realistic realizations, consistent with causality constraints, do lead to a scaling domain wall network with Y-type junctions. We determine the network properties and discuss the corresponding cosmological implications, in particular for dark energy.     

Inflationary predictions at small γ

This Letter explores single field inflation models with a constant, but arbitrary speed of sound cs$c_s$, obtained by deforming the kinetic energy terms to a Dirac–Born–Infeld form. Allowing cs<1$c_s<1$ provides a simple parametrization of non-Gaussianity. The dependence of inflationary observables on the parameter cs$c_s$ is considered in the leading order slow roll approximation. The results show that in most cases the dependence is actually rather weak for the range of cs$c_s$ allowed by existing bounds on non-Gaussianity.     

Varying alpha driven by the Dirac–Born–Infeld scalar field

Since about ten years ago, varying α theories attracted many attentions, mainly due to the first observational evidence from the quasar absorption spectra that the fine structure “constant” might change with cosmological time. In this Letter, we investigate the cosmic evolution of α   driven by the Dirac–Born–Infeld (DBI) scalar field. To be general, we consider various couplings between the DBI scalar field and the electromagnetic field. We also confront the resulting Δα/α$\mathrm{\Delta }\alpha /\alpha$ with the observational constraints, and find that various cosmological evolution histories of Δα/α$\mathrm{\Delta }\alpha /\alpha$ are allowed. Comparing with the case of varying α driven by quintessence, the corresponding constraints on the parameters of coupling have been relaxed, thanks to the relativistic correction of the DBI scalar field.     

Dark energy and the Rutherford–Soddy radiative decay law

It is shown that a putative evolution of the fundamental couplings of strong and weak interactions via coupling to dark energy through a generalized Bekenstein-type model may, for a linear model of variation, cause deviations on the statistical nuclear decay Rutherford–Soddy law unless bounds are imposed on the parameters of this variation. Existing bounds for the weak interaction exclude any significant deviation. Bounds on the strong interaction are much less stringent.     

Stationary ring solitons in field theory — Knots and vortons

We review the current status of the problem of constructing classical field theory solutions describing stationary vortex rings in Minkowski space in 3+1 dimensions. We describe the known up to date solutions of this type, such as the static knot solitons stabilized by the topological Hopf charge, the attempts to gauge them, the anomalous solitons stabilized by the Chern–Simons number, as well as the non-Abelian monopole and sphaleron rings. Passing to the rotating solutions, we first discuss the conditions ensuring that they do not radiate, and then describe the spinning Q$Q$-balls, their twisted and gauged generalizations reported here for the first time, spinning skyrmions, and rotating monopole–antimonopole pairs. We then present the first explicit construction of global vortons as solutions of the elliptic boundary value problem, which demonstrates their non-radiating character. Finally, we describe the analogs of vortons in the Bose–Einstein condensates, analogs of spinning Q$Q$-balls in the non-linear optics, and also moving vortex rings in superfluid helium and in ferromagnetics.     

Early Universe cosmology in the light of the mirror dark matter interpretation of the DAMA/Libra signal

Mirror dark matter provides a simple framework for which to explain the DAMA/LIBRA annual modulation signal consistently with the null results of the other direct detection experiments. The simplest possibility involves ordinary matter interacting with mirror dark matter via photon–mirror photon kinetic mixing of strength ?∼¹⁰⁻⁹$\mathrm{?}\sim {10}^{-9}$. We confirm that photon–mirror photon mixing of this magnitude is consistent with constraints from ordinary Big Bang nucleosynthesis as well as the more stringent constraints from cosmic microwave background measurements and large scale structure considerations.     

Probing the reheating temperature at colliders and with primordial nucleosynthesis

Considering gravitino dark matter scenarios with a long-lived charged slepton, we show that collider measurements of the slepton mass and its lifetime can probe not only the gravitino mass but also the post-inflationary reheating temperature TR$T_{\mathrm{R}}$. In a model independent way, we derive upper limits on TR$T_{\mathrm{R}}$ and discuss them in light of the constraints from the primordial catalysis of ⁶Li through bound-state effects. In the collider-friendly region of slepton masses below 1 TeV, the obtained conservative estimate of the maximum reheating temperature is about TR=3×¹⁰⁹ GeV$T_{\mathrm{R}}=3\times {10}^9\text{GeV}$ for the limiting case of a small gluino–slepton mass splitting and about TR=¹⁰⁸ GeV$T_{\mathrm{R}}={10}^8\text{GeV}$ for the case that is typical for universal soft supersymmetry breaking parameters at the scale of grand unification. We find that a determination of the gluino–slepton mass ratio at the Large Hadron Collider will test the possibility of TR>¹⁰⁹ GeV$T_{\mathrm{R}}>{10}^9\text{GeV}$ and thereby the viability of thermal leptogenesis with hierarchical heavy right-handed Majorana neutrinos.     

Gaussian wave packet states of relic gravitons

In this contribution, we investigate quantum effects of relic gravitons in a Friedmann–Robertson–Walker (FRW) cosmological background. We reduce the problem to that of a generalized time-dependent harmonic oscillator and find the corresponding exact Schrödinger states with the help of linear invariants and of the dynamical invariant method. Afterwards, we construct Gaussian wave packet states and calculate the quantum dispersions as well as the quantum correlations for each mode of the quantized field.     

Cosmological model with viscosity media (dark fluid) described by an effective equation of state

A generally parameterized equation of state (EOS) is investigated in the cosmological evolution with bulk viscosity media modelled as dark fluid, which can be regarded as a unification of dark energy and dark matter. Compared with the case of the perfect fluid, this EOS has possessed four additional parameters, which can be interpreted as the case of the non-perfect fluid with time-dependent viscosity or the model with variable cosmological constant. From this general EOS, a completely integrable dynamical equation to the scale factor is obtained with its solution explicitly given out. (i) In this parameterized model of cosmology, for a special choice of the parameters we can explain the late-time accelerating expansion universe in a new view. The early inflation, the median (relatively late time) deceleration, and the recently cosmic acceleration may be unified in a single equation. (ii) A generalized relation of the Hubble parameter scaling with the redshift is obtained for some cosmology interests. (iii) By using the SNe Ia data to fit the effective viscosity model we show that the case of matter described by p=0$p=0$ plus with effective viscosity contributions can fit the observational gold data in an acceptable level.     

Cosmology with a variable Chaplygin gas

We consider a new generalized Chaplygin gas model that includes the original Chaplygin gas model as a special case. In such a model the generalized Chaplygin gas evolves as from dust to quiescence or phantom. We show that the background evolution for the model is equivalent to that for a coupled dark energy model with dark matter. The constraints from the current type Ia supernova data favour a phantom-like Chaplygin gas model.     

A parametric model for dark energy

Determining the mechanism behind the current cosmic acceleration constitutes a major question nowadays in theoretical physics. If the dark energy route is taken, this problem may potentially bring to light new insights not only in cosmology but also in high energy physics theories. Following this approach, we explore in this Letter some cosmological consequences of a new time-dependent parameterization for the dark energy equation of state (EoS), which is a well behaved function of the redshift z   over the entire cosmological evolution, i.e., z∈[−1,∞)$z\in [-1,\infty )$. This parameterization allows us to divide the parametric plane (w₀,w₁)$(w_0,w_1)$ in defined regions associated to distinct classes of dark energy models that can be confirmed or excluded from a confrontation with current observational data. By assuming a flat universe, a statistical analysis involving the most recent observations from type Ia supernovae, baryon acoustic oscillation peak, Cosmic Microwave Background shift parameter and Hubble evolution H(z)$H(z)$ is performed to check the observational viability of the EoS parameterization here proposed.     

Phenomenological aspects of Hořava–Lifshitz cosmology

We show that, assuming the dispersion relation proposed recently by Ho?ava in the context of quantum gravity, radiation energy density exhibits a peculiar dependence on the scale factor; the radiation energy density decreases proportional to a⁻⁶$a^{\mathrm{-6}}$. This simple scaling can have an impact on cosmology. As an example, we show that the resultant baryon asymmetry as well as the stochastic gravity waves can be enhanced. We also discuss current observational constraint on the dispersion relation.     

Unified picture for Dirac neutrinos,dark matter,dark energy and matter–antimatter asymmetry

We propose a unified scenario to generate the masses of Dirac neutrinos and cold dark matter at the TeV scale, understand the origin of dark energy and explain the matter–antimatter asymmetry of the universe. This model can lead to significant impact on the Higgs searches at LHC.