197530993
Generalized Model for Lambda Dark Energy
119307073
Anisotropic strange star with de Sitter spacetime
Stars can be treated as self-gravitating fluid. Krori and Barua (J. Phys. A., Math. Gen. 8:508, 1975) gave an analytical solution to that kind of fluids. In this connection, we propose a de Sitter model for an anisotropic strange star with the Krori–Barua spacetime. We incorporate the existence of the cosmological constant on a small scale to study the structure of anisotropic strange stars and come to the conclusion that this doping is very well compatible with the well-known physical features of strange stars.
14301959
Do Solar System Tests Permit Higher Dimensional General Relativity?
We perform a survey whether higher dimensional Schwarzschild space-time is compatible with some of the solar system phenomena. As a test we examine four well known solar system effects, viz., (1) Perihelion shift, (2) Bending of light, (3) Gravitational redshift, and (4) Gravitational time delay. It is shown, under a N-dimensional solutions of Schwarzschild type very narrow class of metrics, that the results related to all these physical phenomena are mostly incompatible with the higher dimensional version of general relativity. We compare all these restricted results with the available data in the literature.
15541573
Tolman–Bayin type static charged fluid spheres in general relativity
In a static spherically symmetric Einstein-Maxwell spacetime the class of astrophysical solution found out by Ray and Das (2002) and Pant and Sah (1979) are revisited here in connection to the phenomenological relationship between the gravitational and electromagnetic fields. It is qualitatively shown that the charged relativistic stars of Tolman (1939) and Bayin (1978) type are of purely electromagnetic origin. The existence of this type of astrophysical solutions is a probable extension of Lorentz’s conjecture that electr on-like extended charged particle possesses only ‘electromagnetic mass’ and no ‘material mas s’.
119494697
The Dynamic Cosmological Term $\Lambda$: Some Aspects of Phenomenological Models
Choosing a phenomenological model of $\Lambda$, viz. $\Lambda \sim \dot H$, it has been shown that this model of $\Lambda$ is equivalent to other three types of $\Lambda$, $\Lambda \sim (\dot a/a)^2$, $\Lambda \sim \ddot a/a$ and $\Lambda \sim \rho$. Through an indirect approach, it has also been possible to put a limit on the deceleration parameter $q$. It has been shown that if $q$ becomes less than -1, then this model can predict about the presence of phantom energy.
14627322
The dark energy equation of state
ABSTRACT We perform a study of cosmic evolution with an equation of state parameter ω(t) = ω 0 +ω 1 (tH/H˙ ) by selecting a phenomenological Λ model of the form, Λ˙ ∼ H 3 . This simpleproposition explains both linearly expanding and inﬂation ary Universes with a single set ofequations. We notice that the inﬂation leads to a scaling in t he equation of state parameter,ω(t), and hence in equation of state. In this approach, one of its two parameters have been pinpointed and the other have been delineated. It has been possible to show a connection betweendark energy and Higgs-Boson.Key words: gravitation - cosmological parameters - cosmology: theory- early Universe. 1 INTRODUCTIONCosmological research is mainly concerned with time (and in somecases space as well) evolution of various physical parameters likescale factor, Hubble parameter, matter-energy density etc. Alongwith these parameters, in recent years a new physical entity Λ hasresurrected in the foreground of cosmology. In fact, Λ has becomean essential part of the ﬁeld equations of Einstein after som e ob-servational results (Riess et al. 1998; Perlmutter et al. 1999) indi-cated towards an accelerating Universe. It is believed by most ofthe physicists that the cosmological parameter Λ is responsible fordriving the present acceleration because it can exert negative pres-sure. Moreover, due to some ﬁne-tuning problem (known as cos-mological constant problem), Λ is regarded as a variable quantityrather than a constant.Now, in order to specify exact time-dependence of the un-known physical quantities including Λ, one has to take recourse ofa relationship between cosmic pressure p and matter-energy den-sity ρ involving the equation of state parameter ω. Mathemati-cally speaking, one variable quantity can depend on the productof two other variable quantities. So, one may construct ω as a func-tion of time, red-shift or scale factor (Chervon & Zhuravlev2000;Zhuravlev 2001; Peebles & Ratra 2003). In fact, values of ω at dif-ferent stages of cosmic evolution suggest that it may evolve withtime. As an instance, for the present pressure-less Universe, thevalue of ω is considered as zero, whereas its value was 1/3 in theearly radiation dominated Universe. However, it is convenient toconsider ω as a constant quantity because observational data canhardly distinguish between a varying and a constant equation of
117757665
Equation of state for asymmetric nuclear matter with infinite-order summation of ring diagrams
The particle-particle hole-hole ring-diagram summation method is employed to obtain the equation of state of asymmetric nuclear matter over a wide range of asymmetry fraction. Compared with Brueckner Hartree-Fock and model-space Brueckner Hartree-Fock calculations, this approach gives a softer equation of state, increased symmetry energy and a lower value for the incompressibility modulus which agrees quite well with the values used in the hydrodynamical model for the supernovae explosion.
15882822
Entropy & viscosity bound of strange stars
At finite temperature (T) there is a link with general relativity and hydrodynamics that leads to a lower bound for the ratio of shear viscosity and entropy density (\eta/s). We find that the bound is saturated in the simple model for quark matter that we use for strange stars at T = 80 MeV, at the surface of a strange star. At this T we have the possibility of cosmic separation of phases. We find that, although strongly correlated, the quark matter at the surface of strange stars constitute the most perfect interacting fluid permitted by nature. At the centre of the star, however, the density is higher and conditions are more like the results found for perturbative QCD.
118994296
Signatures of heavy sterile neutrinos at long baseline experiments
Sterile neutrinos with masses {approx}0.1 eV or higher, allowed with the current oscillation data, can potentially play an important role in astrophysics and cosmology. We explore possible signatures of such sterile neutrinos at long baseline experiments. We determine the neutrino conversion probabilities analytically in a 4-neutrino framework, including matter effects, treating the sterile mixing angles {theta}{sub 14}, {theta}{sub 24}, {theta}{sub 34}, the deviation of {theta}{sub 23} from maximality, as well as {theta}{sub 13} and the ratio {delta}m{sub {center_dot}}{sup 2}/{delta}m{sub atm}{sup 2} as small parameters for a perturbative expansion. This gives rise to analytically tractable expressions for flavor conversion probabilities from which effects of these parameters can be clearly understood. We numerically calculate the signals at a neutrino factory with near and far detectors that can identify the lepton charge, and point out observables that can discern the sterile mixing signals. We find that clean identification of sterile mixing would be possible for {theta}{sub 24}{theta}{sub 34} > or approx. 0.005 (3{sigma}) and {theta}{sub 14} > or approx. 0.06 rad (3{sigma}) with the current bound of {theta}{sub 13}<0.2 rad; a better {theta}{sub 13} bound would allow probing smaller values of sterile mixing. We also generalize the formalism for any number of sterilemore » neutrinos, and demonstrate that only certain combinations of sterile mixing parameters are relevant irrespective of the number of sterile neutrinos. This also leads to a stringent test of the scenario with multiple sterile neutrinos that currently is able to describe all the data from the short baseline experiments, including LSND and MiniBooNE.« less
199675394
2540 km: Bimagic baseline for neutrino oscillation parameters
We consider a low energy neutrino factory setup with a detector placed at a distance of 2540 km. At this baseline, for both normal and inverted hierarchical neutrino mass spectrum, the wrong‐sign muon event spectrum is almost independent of CP phase δ and the mixing angle θ13 in a specific energy window. This leads to an unambiguous determination of the hierarchy. In addition, a part of the muon spectrum remain sensitive to δ and θ13, so that the same setup can be used to probe these parameters as well using a broadband beam.
118649508
Renormalization group evolution of neutrino masses and mixing in seesaw models: A Review
We consider different extensions of the standard model which can give rise to the small active neutrino masses through seesaw mechanisms, and their mixing. These tiny neutrino masses are generated at some high energy scale by the heavy seesaw fields which then get sequentially decoupled to give an effective dimension-5 operator. The renormalization group evolution of the masses and the mixing parameters of the three active neutrinos in the high energy as well as the low energy effective theory is reviewed in this article.