Presence Of Matter Fields Research Articles

A new class of regular black holes in Einstein Gauss-Bonnet gravity with localized sources of matter

We provide a new regular black hole solution (RBH) in Einstein Gauss-Bonnet (EGB) gravity with localized sources of matter in the energy–momentum tensor. We determine the necessary constraints in order for the solution to be regular. Although we use a specific form for the energy density as a test of proof, these constraints could serve as a recipe for constructing several new RBH solutions in EGB gravity with localized sources. Due to that the usual first law of thermodynamics is not valid for RBH, so we rewrite the first law for EGB, which leads to correct values of entropy and volume. The size of the extremal black hole, whose temperature vanishes, becomes smaller for larger dimensions, whose radius could be of the order of the Planck units, thus the evaporation would stop once the horizon radius contracts up to a value close to the Planck length, which could be related with the apparition of quantum effects. Furthermore, the presence of matter fields in the energy–momentum tensor induces two phase transitions, where there are two regions of stability. This differs from the vacuum EGB solution, where the specific heat is always negative without phase transition as occurs in Schwarzschild black hole.

Comparison of two theories of Type-IIa minimally modified gravity

We investigate two Type-IIa Minimally Modified Gravity theories, namely VCDM and Cuscuton theories. We confirm that all acceptable Cuscuton solutions are always solutions for VCDM theory. However, the inverse does not hold. We find that VCDM allows for the existence of exact General Relativity (GR) solutions with or without the presence of matter fields and a cosmological constant. We determine the conditions of existence for such GR-VCDM solutions in terms of the trace of the extrinsic curvature and on the fields which define the VCDM theory. On the other hand, for the Cuscuton theory, we find that the same set of exact GR solutions (such as Schwarzschild and Kerr spacetimes) is not compatible with timelike configurations of the Cuscuton field and therefore cannot be considered as acceptable solutions. Nonetheless, in Cuscuton theory, there could exist solutions which are not the same but close enough to GR solutions. We also show the conditions to determine intrinsic-VCDM solutions, i.e. solutions which differ from GR and do not belong to the Cuscuton model. We finally show that in cosmology a mapping between VCDM and the Cuscuton is possible, for a generic form of the VCDM potential. In particular, we find that for a quadratic potential in VCDM theory, this mapping is well defined giving an effective redefinition of the Planck mass for the cosmological background solutions of both theories.

Anomaly-free deformations of spherical general relativity coupled to matter

A systematic approach is developed in order to obtain spherically symmetric midisuperspace models that accept holonomy modifications in the presence of matter fields with local degrees of freedom. In particular, starting from the most general Hamiltonian quadratic in radial derivatives of the variables, we obtain a family of effective modified constraints that satisfy Dirac's deformation algebra, which encodes the covariance of general relativity, and show that (scale-dependent) holonomy corrections can be consistently implemented. In vacuum, the deformed anomaly-free Hamiltonian is explicitly written in terms of three free functions and we obtain a weak observable that can be interpreted as the mass of the model. Finally, as a particular example, we present a specific covariant polymeric model that remains regular for any value of the connection components. Some of its physical implications and the relation with previous studies in the literature are commented.

A new model of regular black hole in (2+1) dimensions

We provide a new regular black hole solution in dimensions with the presence of matter fields in the energy momentum tensor. The inclusion of our proposed energy density plus a negative cosmological constant allows that the solution can have both flat as de Sitter or Anti-de Sitter core. This latter is a proper characteristic of our solution, because other models of regular black holes have only a single type of core. Since the first law of thermodynamics for regular black holes is modified by the presence of the matter fields, we provide a new version of the first law, where a local definition of the variation of energy is defined, and where the entropy and temperature are consistent with the ones previously known in the literature. At the hypothetical limit when the horizon radius the usual first law is recovered. The effectiveness of the formalism used to compute the mass of our regular black holes in dimensions suggests the potential applicability of this method to calculate the mass of other models of regular black holes in dimensions.

Late cosmology in massive conformal gravity

In this paper, we find the cosmological solutions of the massive conformal gravity field equations in the presence of matter fields. In particular, we show that the solution of negative curvature is in good agreement with the late universe.

$T\bar T$ and the mirage of a bulk cutoff

We use the variational principle approach to derive the large NN holographic dictionary for two-dimen-sional T\bar TTT‾-deformed CFTs, for both signs of the deformation parameter. The resulting dual gravitational theory has mixed boundary conditions for the non-dynamical graviton; the boundary conditions for matter fields are undeformed. When the matter fields are turned off and the deformation parameter is negative, the mixed boundary conditions for the metric at infinity can be reinterpreted on-shell as Dirichlet boundary conditions at finite bulk radius, in agreement with a previous proposal by McGough, Mezei and Verlinde. The holographic stress tensor of the deformed CFT is fixed by the variational principle, and in pure gravity it coincides with the Brown-York stress tensor on the radial bulk slice with a particular cosmological constant counterterm contribution. In presence of matter fields, the connection between the mixed boundary conditions and the radial ``bulk cutoff’’ is lost. Only the former correctly reproduce the energy of the bulk configuration, as expected from the fact that a universal formula for the deformed energy can only depend on the universal asymptotics of the bulk solution, rather than the details of its interior. The asymptotic symmetry group associated with the mixed boundary conditions consists of two commuting copies of a state-dependent Virasoro algebra, with the same central extension as in the original CFT.

Nonclassical primordial gravitational waves from the initial entangled state

The nonclassicality of primordial gravitational waves (PGWs) is characterized in terms of sub-Poissonian graviton statistics. The sub-Poissonian statistics are realized when quantum states are squeezed coherent states. In the presence of matter fields, the Universe experiences the squeezed coherent state during inflation. The condition to realize the sub-Poissonian graviton statistics is translated into the frequency range of gravitational waves. If the initial state is the Bunch-Davies vacuum, there is another necessary condition between phases of squeezing and coherent parameters. Here, we extend the initial state to entangled states. We consider $\alpha$-vacua as the initial entangled state that are more general de Sitter invariant vacua than the Bunch-Davies vacuum. We find that, unlike the Bunch-Davies vacuum, PGWs generated in the initial entangled state become sub-Poissonian without requiring the condition between the phases.

Holographic correspondence of F(R) gravity with/without matter fields

In this paper, we apply the holographic principle to the early universe, obtaining an inflation realization of holographic origin. First we show that under the consideration of extended infrared cutoffs, there exists a holographic correspondence of various F(R) (such as quadratic, cubic, exponential F(R) models) cosmological models in the absence of matter fields. Then we establish that such holographic correspondence is not only confined to the vacuum F(R) gravity but also can be extended to the higher curvature models along with matter fields. In the presence of matter field, in particular the second-rank antisymmetric Kalb-Ramond field, all the considered F(R) models lead to a viable inflationary phenomenology consistent with Planck 2018 constraints. We further extend our discussion of holographic correspondence to F(T) cosmological models.

A new scalar–tensor realization of Hořava–Lifshitz gravity

We discuss a new covariant scalar–tensor system aimed to realise Hořava proposal for a power-counting renormalizable theory of gravity, with the special feature of not propagating scalar degrees of freedom in an appropriate gauge. The theory is characterized by a new symmetry acting on the metric, that can protect the particular form of its interactions. The set-up spontaneously breaks Lorentz symmetry by means of a time-like scalar field profile. By selecting a unitary gauge for the scalar, we show that this theory describes the dynamics of a spin two degree of freedom, whose equations of motion contain two time derivatives and up to six spatial derivatives. We analytically determine asymptotically flat, spherically symmetric configurations, showing that there exists a branch of solutions physically equivalent to spherically symmetric configurations in general relativity, also in the presence of matter fields.

Phenomenology of minimal theory of quasidilaton massive gravity

The minimal theory of quasidilaton massive gravity with or without a Horndeski-type kinetic term for the quasidilaton field propagates only three physical modes: the two massive tensor polarizations and one scalar mode. This reduced number of degrees of freedom is realized by a Lorentz symmetry violation at cosmological scales and the presence of appropriate constraints that remove unwanted modes. Vacuum cosmological solutions have been considered in a previous work, and it has been shown that the late-time de Sitter attractor is stable under inhomogeneous perturbations. In this work, we explore the stability of cosmological solutions in the presence of matter fields. Assuming for simplicity that the quasidilaton scalar is on an attractor at the level of the background, we derive stability conditions in the subhorizon limit, and find the scalar sound speeds, as well as the modification with respect to general relativity to the gravitational potential in the quasistatic approximation. We also find that the speed limit of gravitational waves coincides with the speed of light for any homogeneous and isotropic cosmological background, on or away from the attractor.

Asymptotic safety of gravity with matter

We study the asymptotic safety conjecture for quantum gravity in the presence of matter fields. A general line of reasoning is put forward explaining why gravitons dominate the high-energy behaviour, largely independently of the matter fields as long as these remain sufficiently weakly coupled. Our considerations are put to work for gravity coupled to Yang-Mills theories with the help of the functional renormalisation group. In an expansion about flat backgrounds, explicit results for beta functions, fixed points, universal exponents, and scaling solutions are given in systematic approximations exploiting running propagators, vertices, and background couplings. Invariably, we find that the gauge coupling becomes asymptotically free while the gravitational sector becomes asymptotically safe. The dependence on matter field multiplicities is weak. We also explain how the scheme dependence, which is more pronounced, can be handled without changing the physics. Our findings offer a new interpretation of many earlier results, which is explained in detail. The results generalise to theories with minimally coupled scalar and fermionic matter. Some implications for the ultraviolet closure of the Standard Model or its extensions are given.

On the stability conditions for theories of modified gravity in the presence of matter fields

We present a thorough stability analysis of modified gravity theories in the presence of matter fields. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all the scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical behaviours which in turn lead to a stable and an unstable configuration. Moreover, we find that the speeds of propagation of the scalar modes strongly depend on matter densities, for the beyond Horndeski theories. Our findings can be directly employed when testing modified gravity theories as they allow to identify the correct viability space.

A 3D Brans-Dicke Theory Model

The evidence of an accelerated universe and the gap of 70 percent in the total energy, collected by WMAP, are problems that cannot be solved by standard models based on General relativity. Therefore the search for an alternative theory that solves the open questions in General Relativity became an important research field in the past few years. A particular alternative is the Brans-Dicke theory, which has been broadly studied as concerned to k-essence type fields in 4D. However, this theory is almost unexplored in the context of the dimensional reduction in 3D. In the present work, we study the Brans-Dicke Theory in a dimensional reduction context. In order to do this, we consider the Brans-Dicke theory in the vacuum, and in the presence of matter fields.

Revisiting perturbations in extended quasidilaton massive gravity

In this work we study the theory of extended quasidilaton massive gravity together with the presence of matter fields. After discussing the homogeneous and isotropic fully dynamical background equations, which governs the exact expansion history of the universe, we consider small cosmological perturbations around these general FLRW solutions. The stability of tensor, vector and scalar perturbations on top of these general background solutions give rise to slightly different constraints on the parameters of the theory than those obtained in the approximative assumption of the late-time asymptotic form of the expansion history, which does not correspond to our current epoch. This opens up the possibility of stable FLRW solutions to be compared with current data on cosmic expansion with the restricted parameter space based on theoretical ground.

Quasilocal conserved charges and holography

We construct a quasi-local formalism for conserved charges in a theory of gravity in the presence of matter fields which may have slow falloff behaviors at the asymptotic infinity. This construction depends only on equations of motion and so it is irrespective of ambiguities in the total derivatives of the Lagrangian. By using identically conserved currents, we show that this formalism leads to the same expressions of conserved charges as those in the covariant phase space approach. At the boundary of the asymptotic AdS space, we also introduce an identically conserved boundary current which has the same structure as the bulk current and then show that this boundary current gives us the holographic conserved charges identical with those from the boundary stress tensor method. In our quasi-local formalism we present a general proof that conserved charges from the bulk potential are identical with those from the boundary current. Our results can be regarded as the extension of the existing results on the equivalence of conserved charges by the covariant phase space approach and by the boundary stress tensor method.

SU(2) gauge symmetry in gravity phase space

The Hamiltonian formulation of the Holst action in vacuum and in the presence of matter fields is analyzed in a generic local Lorentz frame. It is elucidated how the SU(2) gauge symmetry is inferred by reducing the set of constraints to a first-class one. The consequences of the proposed approach for Loop Quantum Gravity and Spin Foam models are discussed.

Goldstino and sgoldstino in microscopic models and the constrained superfields formalism

We examine the exact relation between the superconformal symmetry breaking chiral superfield ( X) and the goldstino superfield in microscopic models of an arbitrary Kahler potential ( K) and in the presence of matter fields. We investigate the decoupling of the massive sgoldstino and scalar matter fields and the offshell/onshell-SUSY expressions of their superfields in terms of the fermions composites. For general K of two superfields, we study the properties of the superfield X after integrating out these scalar fields, to show that in the infrared it satisfies (offshell) the condition X 3 = 0 and X 2 ≠ 0 . We then compare our results to those of the well-known method of constrained superfields discussed in the literature, based on the conjecture X 2 = 0 . Our results can be used in applications, to couple offshell the (s)goldstino fields to realistic models such as the MSSM.

Cosmology in nonrelativistic general covariant theory of gravity

Horava and Melby-Thompson recently proposed a new version of the Horava-Lifshitz theory of gravity, in which the spin-0 graviton is eliminated by introducing a Newtonian prepotential $\ensuremath{\varphi}$ and a local $U(1)$ gauge field $A$. In this paper, we first derive the corresponding Hamiltonian, supermomentum constraints, the dynamical equations, and the equations for $\ensuremath{\varphi}$ and $A$, in the presence of matter fields. Then, we apply the theory to cosmology and obtain the modified Friedmann equation and the conservation law of energy, in addition to the equations for $\ensuremath{\varphi}$ and $A$. When the spatial curvature is different from zero, terms behaving like dark radiation and stiff-fluid exist, from which, among other possibilities, a bouncing universe can be constructed. We also study linear perturbations of the Friedmann-Robertson-Walker universe with any given spatial curvature $k$, and we derive the most general formulas for scalar perturbations. The vector and tensor perturbations are the same as those recently given by one of the present authors [A. Wang, Phys. Rev. D 82, 124063 (2010).] in the setup of Sotiriou, Visser, and Weinfurtner. Applying these formulas to the Minkowski background, we have shown explicitly that the scalar and vector perturbations of the metric indeed vanish, and the only remaining modes are the massless spin-2 gravitons.

A note on moduli stabilisation in heterotic models in the presence of matter fields

In this brief note we analyse a toy model which can be derived from heterotic string compactifications on half-flat manifolds with SU(3) structure at first order in α′ (i.e. including matter fields). We show that for this model, finding solutions with viable gauge group poses the same problems as finding solutions in the absence of matter fields.

Moduli evolution in the presence of matter fields and flux compactification

We provide a detailed analysis of the dynamics of moduli fields in the KKLT scenariocoupled to a Polonyi field, which plays the role of a hidden matter sector field. It waspreviously shown that such matter fields can uplift AdS vacua to Minkowski or de Sittervacua. Additionally, we take a background fluid into account (which can be either matteror radiation), which aids moduli stabilization. Our analysis shows that the presence of thematter field further aids stabilization, due to a new scaling regime. We study the systemboth analytically and numerically.