59046703
Wormhole inspired by non-commutative geometry
In the present letter we search for a new wormhole solution inspired by noncommutative geometry with the additional condition of allowing conformal Killing vectors (CKV). A special aspect of noncommutative geometry is that it replaces point-like structures of gravitational sources with smeared objects under Gaussian distribution. However, the purpose of this paper is to obtain wormhole solutions with noncommutative geometry as a background where we consider a point-like structure of gravitational object without smearing effect. It is found through this investigation that wormhole solutions exist in this Lorentzian distribution with viable physical properties.
117429531
Periodicity of ~155 days in solar electron fluence
In this paper we have investigated the occurrence rate of high energetic(E>10 MeV) solar electron flares measured by IMP-8 spacecraft of NASA for solar cycle 21 (June, 1976 to August, 1986) first time by three different methods to detect periodicities accurately. Power-spectrum analysis confirms a periodicity ~155 days which is in consistent with the result of Chowdhury and Ray (2006), that "Rieger periodicity" was operated throughout the cycle 21 and it is independent on the energy of the electron fluxes.
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.
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
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’.
118317908
CP asymmetry in the decays B ---> (X(s), X(d)) mu+ mu- with four generations
We estimate the CP asymmetry A CP (q 2 ) in the decays B → X s μ + μ - and B → X d μ + μ in the standard model (SM) with an additional fourth generation. We use a parametrization that allows us to explore the complete parameter space of the 4 X 4 quark mixing matrix, and constrain these parameters from the current data on B decays. We find that the enhancement in A CP (q 2 ) depends strongly on the mass of the t 1 , the up-type quark in the fourth generation. For m t 1 around 400 GeV, the CP asymmetry in the high-q 2 region (q 2 > 14.4 GeV 2 ) can be enhanced by more than an order of magnitude for B → X s μ + μ - and up to a factor of 6 for B → X d μ + μ - . There is no enhancement in the low-q 2 region (1 < q 2 < 6 GeV 2 ). With increasing m t 1 , A CP (q 2 ) in the high-q 2 (low-q 2 ) region first decreases (increases) and then saturates at a value a few times the SM prediction. In the high-q 2 region of B → X s μ + μ - , this saturation value may be up to 25 times the SM expectation.
13958309
Evidence for strange stars from joint observation of harmonic absorption bands and of redshift
From recent reports on terrestrial heavy ion collision experiments it appears that one may not obtain information about the existence of asymptotic freedom (AF) and chiral symmetry restoration (CSR) for quarks of QCD at high density. This information may still be obtained from compact stars – if they are made up of strange quark matter (SQM). 
 
 
 
Very high gravitational redshift lines (GRL), seen from some compact stars, seem to suggest high ratios of mass and radius (M/R) for them. This is suggestive of strange stars (SS) and can in fact be fitted very well with SQM equation of state (EOS) deduced with built in AF and CSR. In some other stars broad absorption bands (BAB) appear at about ∼0.3 keV and multiples thereof, that may fit in very well with resonance with harmonic compressional breathing mode frequencies of these SS. Emission at these frequencies are also observed in six stars. 
 
 
 
If these two features of large GRL and BAB were observed together in a single star, it would strengthen the possibility for the existence of SS in nature and would vindicate the current dogma of AF and CSR that we believe in QCD. Recently, in 4U 1700 − 24, both features appear to be detected, which may well be interpreted as observation of SS – although the group that analyzed the data did not observe this possibility. We predict that if the shifted lines, that has been observed, are from neon with GRL shift z= 0.4– then the compact object emitting it is a SS of mass 1.2 M⊙ and radius 7 km. In addition the fit to the spectrum leaves a residual with broad dips at 0.35 keV and multiples thereof, as in 1E 1207 − 5209 which is again suggestive of SS.
119301631
Some simple models for quark stars
We find two new classes of exact solutions for the Einstein-Maxwell equations. The solutions are obtained by considering charged anisotropic matter with a linear equation of state consistent with quark stars. The field equations are integrated by specifying forms for the measure of anisotropy and a gravitational potential which are physically reasonable. The solutions found generalize the Mark-Harko model and the Komathiraj-Maharaj model. A graphical analysis indicates that the matter variables are well behaved.
8136121
Chromo-thermal instabilities and collapse of quark stars to black holes Astrophysical Implications
We have studied the effects of temperature on the properties of strange stars. We find that the maximum mass of the strange star decreases with the increase of temperature, because at high temperatures the equation of states become softer. Moreover, if the temperature of a strange star increases keeping its baryon number fixed, its gravitational mass increases and radius decreases which leads to a limiting temperature where it turns into a black hole. These features of strange stars is a combined effect of change of gluon mass and the quark distribution function with temperature. We have discovered a new kind of radial oscillations of strange stars driven by what we named chromo-thermal instability. This instability and the related radial oscillations of the star is inherent to strange quark matter making strange stars even more exotic than neutron stars within astrophysical context. In particular, we discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma ray bursts. Subject headings: compact object – neutron star – strange star – black hole – GRB – afterglow
119180962
CPT violation in long baseline neutrino experiments: A three flavor analysis
We explore possible signals of CPT violation in neutrinos in the complete three-flavor framework. Employing a systematic expansion in small parameters, we analytically estimate the CPT violating contributions to the survival probabilities of ${\ensuremath{\nu}}_{\ensuremath{\mu}}$, ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$, ${\ensuremath{\nu}}_{e}$ and, ${\overline{\ensuremath{\nu}}}_{e}$. The results indicate that, in spite of the large number of CPT violating parameters, only a small number of combinations are relevant for oscillation experiments. We identify the combinations that can be constrained at the long baseline experiments, and show that their contribution to the neutrino Hamiltonian can be bounded to $\ensuremath{\lesssim}{10}^{\ensuremath{-}23}\text{ }\text{ }\mathrm{GeV}$, by considering the NOvA experiment for the muon sector, and neutrino factories for the electron sector. This formalism also allows us to translate the bounds on the parameters describing non-standard interactions of neutrinos into the bounds on CPT violating quantities.