Featured Researches

General Relativity And Quantum Cosmology

A Conformally Flat Generalized Ricci Recurrent Spacetime in F(R)-Gravity

In the present paper we study a conformally flat generalized Ricci recurrent perfect fluid spacetime with constant Ricci scalar as a solution of modified F(R) -gravity theory. We show that a Robertson-Walker spacetime is generalized Ricci Recurrent if and only if it is Ricci symmetric. The perfect fluid type matter is shown to have EoS ?=?? . Some energy conditions are analyzed with couple of popular toy models of F(R) -gravity, like F(R)=R+α R m where α,m are constants and F(R)=R+βRlnR where β is constant. In harmony with the recent observational studies of accelerated expansion of the universe, both cases exhibit that the null, weak, and dominant energy conditions fulfill their requirements whereas the strong energy condition is violated.

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General Relativity And Quantum Cosmology

A Critique of Holographic Dark Energy

Observations restrict the parameter space of Holographic Dark Energy (HDE) so that a turning point in the Hubble parameter H(z) is inevitable. Concretely, cosmic microwave background (CMB), baryon acoustic oscillations (BAO) and Type Ia supernovae (SNE) data put the turning point in the future, but removing SNE results in an observational turning point at positive redshift. From the perspective of theory, not only does the turning point violate the Null Energy Condition (NEC), but as we argue, it leads to a potential evolution of the Hubble constant H 0 with redshift, which is at odds with the cosmological principle. Tellingly, neither of these are problems for the flat ? CDM model, and a direct comparison of fits further disfavours HDE relative to flat ? CDM.

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General Relativity And Quantum Cosmology

A New Torsion Balance for the Search of Long-range Interactions Coupling to Baryon and Lepton Numbers

We have developed a torsion balance with a sensitivity about ten times better than those of previously operating balances for the study of long range forces coupling to baryon and lepton number. We present here the details of the design and expected characteristics of this balance. Operation of this balance for a year will also result in improved bounds on long range interactions of dark matter violating Einstein's equivalence principle.

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General Relativity And Quantum Cosmology

A Note on Effects of Generalized and Extended Uncertainty Principles on Jüttner Gas

In recent years, the implications of the generalized (GUP) and extended (EUP) uncertainty prin-ciples on Maxwell-Boltzmann distribution have been widely investigated. However, at high energy regimes, the validity of Maxwell-Boltzmann statistics is under debate and instead, the Jüttner distribution is proposed as the distribution function in relativistic limit. Motivated by these considerations, in the present work, our aim is to study the effects of GUP and EUP on a system that obeys the Jüttner distribution. To achieve this goal, we address a method to get the distribution function by starting from the partition function and its relation with thermal energy which finally helps us in finding the corresponding energy density states.

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General Relativity And Quantum Cosmology

A Relativistic Stellar Model for Pulsar PSR B0943+10 with Vaidya-Tikekar Ansatz

This paper presents an exact solution of the Einstein-Maxwell field equations in a static and spherically symmetric Schwarzschild canonical coordinate system in the presence of charged perfect fluid. We have employed the Vaidya-Tikekar ansatz for the metric potential. Using graphical analysis and tabular information we have shown that our model obeys all the physical requirements and stability conditions required for a realistic stellar model. This theoretical model approximates observations of pulsar PSR B0943+10 to an excellent degree of accuracy.

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General Relativity And Quantum Cosmology

A Study On Some Geometric and Physical Properties of Hyper-Generalised Quasi-Einstein Spacetime

In the present paper we discuss about a set of geometric and physical properties of hyper-generalised quasi-Einstein spacetime. At the beginning we discuss about pseudosymmetry over a hyper-generalised quasi-Einstein spacetime. Here we discuss about W2-Ricci pseudosymmetry, Z-Ricci pseudosymmetry, Ricci pseudosymmetry and projective pseudosymmetry over a hyper-generalised quasi-Einstein spacetime. Later on we take over Ricci symmetric hyper-generalised quasi-Einstein spacetime and derive a set of important geometric and physical theorems over it. Moving further we consider some physical applications of the hyper-generalised quasi-Einstein spacetime. Lastly we prove the existence of a hyper-generalised quasi-Einstein spacetime by constructing a non-trivial example.

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General Relativity And Quantum Cosmology

A comparison theorem for cosmological lightcones

Let (M,g) denote a cosmological spacetime describing the evolution of a universe which is isotropic and homogeneous on large scales, but highly inhomogeneous on smaller scales. We consider two past lightcones, the first, C ??L (p,g) , is associated with the physical observer p?�M who describes the actual physical spacetime geometry of (M,g) at the length scale L , whereas the second, C ??L (p, g ^ ) , is associated with an idealized version of the observer p who, notwithstanding the presence of local inhomogeneities at the given scale L , wish to model (M,g) with a member (M, g ^ ) of the family of Friedmann-Lemaitre-Robertson-Walker spacetimes. In such a framework, we discuss a number of mathematical results that allows a rigorous comparison between the two lightcones C ??L (p,g) and C ??L (p, g ^ ) . In particular, we introduce a scale dependent ( L ) lightcone-comparison functional, defined by a harmonic type energy, associated with a natural map between the physical C ??L (p,g) and the FLRW reference lightcone C ??L (p, g ^ ) . This functional has a number of remarkable properties, in particular it vanishes iff, at the given length-scale, the corresponding lightcone surface sections (the celestial spheres) are isometric. We discuss in detail its variational analysis and prove the existence of a minimum that characterizes a natural scale-dependent distance functional between the two lightcones. We also indicate how it is possible to extend our results to the case when caustics develop on the physical past lightcone C ??L (p,g) . Finally, we show how the distance functional is related to spacetime scalar curvature in the causal past of the two lightcones, and briefly illustrate a number of its possible applications.

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General Relativity And Quantum Cosmology

A covariant polymerized scalar field in loop quantum gravity

We propose a new polymerization scheme for scalar fields coupled to gravity. It has the advantage of being a (non-bijective) canonical transformation of the fields and therefore ensures the covariance of the theory. We study it in detail in spherically symmetric situations and compare to other approaches.

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General Relativity And Quantum Cosmology

A finite model of an elementary charge

We set up a model of an elementary electric charge where the noninvertible metric phase of first order gravity supercedes the standard point singularity. A topological interpretation of the electric charge is provided in terms of an index defined for the degenerate spacetime solution, being closely related to the Euler characteristic. The gravitational equations of motion at this phase are found to be equivalent to the laws of electrostatics. The associated field energy is finite and the geometry sourcing the charge is regular.

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General Relativity And Quantum Cosmology

A higher-multipole gravitational waveform model for an eccentric binary black holes based on the effective-one-body-numerical-relativity formalism

We construct a new factorized waveform including (l,|m|)=(2,2),(2,1),(3,3),(4,4) modes based on effective-one-body (EOB) formalism, which is valid for spinning binary black holes (BBH) in general equatorial orbit. When combined with the dynamics of SEOBNRv4 , the (l,|m|)=(2,2) mode waveform generated by this new waveform can fit the original SEOBNRv4 waveform very well in the case of a quasi-circular orbit. We have calibrated our new waveform model to the Simulating eXtreme Spacetimes (SXS) catalog. The comparison is done for BBH with total mass in (20,200) M ??using Advanced LIGO designed sensitivity. For the quasi-circular cases we have compared our (2,2) mode waveforms to the 281 numerical relativity (NR) simulations of BBH along quasi-circular orbits. All of the matching factors are bigger than 98\%. For the elliptical cases, 24 numerical relativity simulations of BBH along an elliptic orbit are used. For each elliptical BBH system, we compare our modeled gravitational polarizations against the NR results for different combinations of the inclination angle, the initial orbit phase and the source localization in the sky. We use the the minimal matching factor respect to the inclination angle, the initial orbit phase and the source localization to quantify the performance of the higher modes waveform. We found that after introducing the high modes, the minimum of the minimal matching factor among the 24 tested elliptical BBHs increases from 90\% to 98\%. Following our previous SEOBNRE waveform model, we call our new waveform model SEOBNREHM . Our SEOBNREHM waveform model can match all tested 305 SXS waveforms better than 98\% including highly spinning ( ?=0.99 ) BBH, highly eccentric ( e??.15 ) BBH and large mass ratio ( q=10 ) BBH.

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