Relativistic strange quark stars in Lovelock gravity

Abstract

We study relativistic non-rotating stars in the framework of Lovelock gravity. In particular, we consider the Gauss-Bonnet term in a five-dimensional spacetime, and we investigate the impact of the Gauss-Bonnet parameter on properties of the stars, both isotropic and anisotropic. For matter inside the star, we assume a relativistic gas of de-confined massless quarks. We integrate the modified Tolman-Oppenheimer-Volkoff equations numerically, and we obtain the mass-to-radius profile, the compactness of the star as well as the gravitational red-shift for several values of the Gauss-Bonnet parameter. The maximum star mass and radius are also reported. PACS. XX.XX.XX No PACS code given 1 IntroductionAlthough our observable Universe is clearly four-dimensional, the question "How many dimensions are there?" is one of the fundamental questions High Energy Physics tries to answer. Kaluza-Klein theories [1,2], supergravity [3] and Superstring/M-Theory [4,5] have pushed forward the idea that extra spatial dimensions may exist. In more than four dimensions higher order curvature terms are natural in Lovelock theory [6], and also higher order curvature corrections appear in the low-energy effective equations of Superstring Theory [7].The amount of published works in the literature reveals that Lovelock gravity is an exciting and active field. Black hole physics [8][9][10][11][12][13][14], cosmological solutions [15][16][17][18] and holographic superconductors exploiting the gauge/gravity duality [19] are some of the areas that have been explored in the framework of Lovelock gravity. However, the astrophysical implications of Lovelock theory should also be investigated. Compact objects [20][21][22], such as white dwarfs and neutron stars, are the final fate of stars, and comprise excellent cosmic laboratories to study, test and constrain new physics and/or alternative theories of gravity under extreme conditions that cannot be reached in Earth-based experiments. It is well-known that the properties of compact objects, such as mass and radius, depend both on the equation-of-state (EoS) of ultra-dense matter and on the underlying theory of gravity.A couple of years after the discovery of the neutron by James Chadwick [23,24], neutron stars were predicted to exist by Baade and Zwicky [25]. Indeed, several decades after that, the discoveries of pulsars in the Crab and Vela supernova remnants [26] led to their identification as neutron stars just one year after the discovery of pulsars in 1967 [27]. On the other hand quark matter is by assumption absolutely stable, and as such it may be the true ground state of hadronic matter [28,29]. Therefore a new class of hypothetical compact objects has been postulated to exist. These compact objects could serve as an alternative to neutron stars, and they might offer us a plausible explanation of the puzzling observation of some super-luminous supernovae [30,31], which occur in about one out of every 1000 supernovae explosions, and which are more than 100 times more luminous than regular su...

Stellar structure models in modified theories of gravity: Lessons and challenges

“…where we recall that the star surface is defined as the point where P(r S ) = 0 supplemented with the conditions P r = 0 and P rr = 0 in order to guarantee a smooth matching with the exterior. Together with (281), this gives…”

“…The simplest member of this family is perhaps Gauss-Bonnet gravity, with f 1 = 1 and any other function vanishing, whose five-dimensional case was considered by Panotopoulos and Rincón in [281]. Casting the TOV equations in this case, they numerically integrate them for strange quark matter, where the EOS (94) is replaced by P = 1 4 (ρ−5B) due to the presence of extra dimensions.…”

Interior solutions of relativistic stars with anisotropic matter in scale-dependent gravity

“…Also, close-related approaches share the similar foundations, for instance the well-known Renormalization group improvement method [70][71][72][73] (usually applied to black hole physics) or the running vacuum approach [74][75][76][77][78][79] (usually implemented in cosmological models). Following the same philosophy, recently the scale-dependent gravity have provided non-trivial black holes solutions as well as cosmological solutions, investigating different conceptual aspects of such novel results (see, for instance [80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96] and references therein). Roughly speaking, scaledependent gravity extend classical general relativity solutions after treat the classical coupling as scale-dependent functions, which can be symbolically represented as follows…”

“…Next, regarding energy conditions, we require that [40][41][42]113,114] WEC: ρ ≥ 0 , ρ + p r,t ≥ 0 , (…”

Quark stars with isotropic matter in Hořava gravity and Einstein–æther theory

“…Therefore, as a final check we investigate if the (i) energy conditions and (ii) stability criteria are fulfilled or not. Concerning the energy conditions, we require that [72][73][74][75][76]:…”