119230920
Reheating the Universe in Braneworld Cosmological Models with bulk-brane energy transfer
The emergence of the cosmological composition (the reheating era) after the inflationary period is analyzed in the framework of the braneworld models, in which our Universe is a three-brane embedded in a five-dimensional bulk, by assuming the possibility of the brane-bulk energy exchange. The inflaton field is assumed to decay into normal matter only, while the dark matter is injected into the brane from the bulk. To describe the reheating process we adopt a phenomenological approach, by describing the decay of the inflaton field by a friction term proportional to the energy density of the field. After the radiation dominated epoch the model reduces to the standard four dimensional cosmological model. The modified field equations are analyzed analytically and numerically in both the extra-dimensions dominate reheating phase (when the quadratic terms in energy density dominate the dynamics), and in the general case. The evolution profiles of the matter, of the scalar field and of the scale factor of the universe are obtained for different values of the parameters of the model, and of the equations of state of the normal and dark matter, respectively. The equation describing the time evolution of the ratio of the energy density of the dark and of the normal matter is also obtained. The ratio depends on the rate of the energy flow between the bulk and the brane. The observational constraint of an approximately constant ratio of the dark and of the baryonic matter requires that the dark matter must be non-relativistic (cold). The model predicts a reheating temperature of the order of 3 × 10 6 GeV, a brane tension of the order of 10 25 GeV 4 , and the obtained composition of the universe is consistent with the observational data.
119217960
Inflating wormholes in the braneworld models
The braneworld model, in which our Universe is a three-brane embedded in a five-dimensional bulk, allows the existence of wormholes, without any violation of the energy conditions. A fundamental ingredient of traversable wormholes is the violation of the null energy condition (NEC). However, in the braneworld models, the stress–energy tensor confined on the brane, threading the wormhole, satisfies the NEC. In conventional general relativity, wormholes existing before inflation can be significantly enlarged by the expanding spacetime. We investigate the evolution of an inflating wormhole in the braneworld scenario, in which the wormhole is supported by the nonlocal braneworld effects. As a first step in our study, we consider the possibility of embedding a four-dimensional braneworld wormhole into a five-dimensional bulk. The conditions for the embedding are obtained by studying the junction conditions for the wormhole geometry, as well as the full set of the five-dimensional bulk field equations. For the description of the inflation, we adopt the chaotic inflation model. We study the dynamics of the braneworld wormholes during the exponential inflation stage, and in the stage of the oscillating scalar field. A particular exact solution corresponding to a zero redshift wormhole is also obtained. The resulting evolution shows that while the physical and geometrical parameters of a zero redshift wormhole decay naturally, a wormhole satisfying some very general initial conditions could turn into a black hole and exist forever.
118343376
Inflation and late-time acceleration in braneworld cosmological models with varying brane tension
Braneworld models with variable brane tension λ introduce a new degree of freedom that allows for evolving gravitational and cosmological constants, the latter being a natural candidate for dark energy. We consider a thermodynamic interpretation of the varying brane tension models, by showing that the field equations with variable λ can be interpreted as describing matter creation in a cosmological framework. The particle creation rate is determined by the variation rate of the brane tension, as well as by the brane–bulk energy-matter transfer rate. We investigate the effect of a variable brane tension on the cosmological evolution of the Universe, in the framework of a particular model in which the brane tension is an exponentially dependent function of the scale factor. The resulting cosmology shows the presence of an initial inflationary expansion, followed by a decelerating phase, and by a smooth transition towards a late accelerated de Sitter type expansion. The varying brane tension is also responsible for the generation of the matter in the Universe (reheating period). The physical constraints on the model parameters, resulting from the observational cosmological data, are also investigated.
118580751
Weyl fluid dark matter model tested on the galactic scale by weak gravitational lensing
The higher-dimensional Weyl curvature induces on the brane a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies spacetime geometry around galaxies and has been shown to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in the dark radiation dominated region of galaxies in a class of spherically symmetric braneworld metrics. We find that the lensing profile in the braneworld scenario is distinguishable from dark matter lensing, despite both the braneworld scenario and dark matter models fitting the rotation curve data. In particular, in the asymptotic regions, light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid, we further find a critical radius below which braneworld effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, the addition of which always increases the deflection angle.
118515768
THE EFFECT OF ENVIRONMENT ON SHEAR IN STRONG GRAVITATIONAL LENSES
Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight (LOS) galaxies on the lens potential. We use Monte Carlo simulations to derive the shear directly from measurements of the complex lens environment, providing the first detailed independent check of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by varying the fraction of total mass apportioned between the group dark matter halo and individual group galaxies. The environment produces an average shear of γ = 0.08 (ranging from 0.02 to 0.17), significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears do not match those obtained from lens modeling in three of the six four-image systems in our sample (B1422, RXJ1131, and WFI2033). The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is γ = 0.05 (ranging from 0.01 to 0.14), indicating that LOS contributions to the lens potential are not negligible. We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, the scatter in the Faber-Jackson relation and error in the group centroid position dominate. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the LOS, particularly those bright (I< 21.5) galaxies projected within 5' of the lens.
122661013
MULTIMONOPOLE–ANTIMONOPOLE SOLUTIONS OF THE SU(2) YANG–MILLS–HIGGS FIELD THEORY
In this paper we constructed exact static multimonopole–antimonopole solutions of the YMH field theory. By labelling these solutions as A1, A2, B1, and B2, we notice that the exact axially symmetric 1-monopole — two antimonopoles solution is actually a special case of the A1 solution when the topological index parameter m=1. Also the B1 solution will reduce to a spherically symmetric Wu–Yang type monopole of unit charge when m=0. All these exact solutions satisfy the first order Bogomol'nyi equations and possess infinite energy. Hence they are a different type of the BPS solution. Except for the A1 solution when m=1 and the B1 solution when m=0, these solutions in general do not possess axial symmetry. They represent different combinations of monopoles, multimonopole, and antimonopoles, symmetrically arranged about the z-axis.
119481039
STATIC MONOPOLES AND THEIR ANTICONFIGURATIONS
Recently, we have reported on the existence of some monopoles, multimonopole, and antimonopoles configurations. In this paper we would like to present more monopoles, multimonopole, and antimonopoles configurations of the magnetic ansatz of Ref. 9 when the parameters p and b of the solutions takes different serial values. These exact solutions are a different kind of BPS solution. They satisfy the first order Bogomol'nyi equation but possess infinite energy. They can have radial, axial, or rotational symmetry about the z-axis. We classified these serial solutions as (i) the multimonopole at the origin; (ii) the finitely separated 1-monopoles; (iii) the screening solutions of multimonopole and (iv) the axially symmetric monopole solutions. We also give a construction of their anticonfigurations with all the magnetic charges of poles in the configurations reversed. Half-integer topological magnetic charge multimonopole also exist in some of these series of solutions.
119199675
Comments on the Monopole-Antimonopole Pair Solutions
Recently, the monopole-antimonopole pair and monopole-antimonopole chain solutions are solved with internal space coordinate system of -winding number m greater than one. However, we notice that it is also possible to solve these solutions numerically in terms of -winding number m = 1 instead. When m = 1, the exact asymptotic solutions at small and large distances are parameterized by a single integer parameter s. Here we once again study the monopole-antimonopole pair solution of the SU(2) YangMills-Higgs theory which belongs to the topological trivial sector numerically in its new form. This solution with -winding and -winding number one is parameterized by s = 0 at small r and s = 1 at large r.
119270486
Monopole–antimonopole pair dyons with critical electric charges
In this paper, we investigate some electrically charged magnetic solutions of the SU(2) Yang–Mills–Higgs field theory in the net-zero topological charge sector. We only examine the case when the Higgs field vanishes at two points along the z-axis and when the Higgs field vanishes along a ring with the z-axis as its symmetry axis. We study the possible electric charges the dyons can carry in relation to the electric–magnetic charge separations and calculate the finite total energy and magnet dipole moment of these dyons. These stationary dyon solutions do not satisfy the first-order Bogomol’nyi equations and are non-BPS solutions. They are axially symmetric saddle-point solutions and are characterized by the electric charge parameter, −1 < η < 1, which determines the net electric charges of these dyons. These dyon solutions are solved numerically when the magnetic charges are n = 1, 2, 3, 4 and 5, and when the strength of the Higgs field potential is non-vanishing with λ = 1. When λ = 1, we found that the net electric charge approaches a finite critical value as η approaches ±1. Hence the electromagnetic charge separation, total energy and magnetic dipole moment of the dyon also approach a finite critical value.