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Suresh Kumar - One of the best experts on this subject based on the ideXlab platform.

  • anisotropic dark energy models with Constant Deceleration parameter
    General Relativity and Gravitation, 2011
    Co-Authors: Suresh Kumar, C P Singh
    Abstract:

    We consider a spatially homogeneous and totally anisotropic Bianchi-I space-time with perfect fluid (dark matter and standard visible matter) and anisotropic dark energy, which has dynamical energy density. The two sources are assumed to interact minimally and therefore their energy momentum tensors are conserved separately. Using suitable physical assumptions, the field equations are solved exactly. Various dark energy models are studied and it is found that quintessence model is suitable for describing the present evolution of the universe. The geometrical and kinematical features of the models and the behavior of the anisotropy of the dark energy, are examined in detail.

  • anisotropic bianchi type i models with Constant Deceleration parameter in general relativity
    Astrophysics and Space Science, 2007
    Co-Authors: Suresh Kumar, C P Singh
    Abstract:

    A special law of variation for Hubble’s parameter is presented in a spatially homogeneous and anisotropic Bianchi type-I space-time that yields a Constant value of Deceleration parameter. Using the law of variation for Hubble’s parameter, exact solutions of Einstein’s field equations are obtained for Bianchi-I space-time filled with perfect fluid in two different cases where the universe exhibits power-law and exponential expansion. It is found that the solutions are consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out.

  • bianchi type ii space times with Constant Deceleration parameter in self creation cosmology
    Astrophysics and Space Science, 2007
    Co-Authors: C P Singh, Suresh Kumar
    Abstract:

    The properties of locally rotationally symmetric Bianchi type-II perfect fluid space-times are analyzed in Barber’s second self-creation theory by using a special law of variation for Hubble’s parameter that yields a Constant value of Deceleration parameter. By assuming the equation of state p=γρ, many new solutions are obtained for different era—Zel’dovich, radiation, vacuum and vacuum energy dominated. The solutions with power-law and exponential expansion are discussed. A detailed study of geometrical and physical parameters is carried out. The nature of singularity is also clarified in each case.

  • bianchi type ii cosmological models with Constant Deceleration parameter
    International Journal of Modern Physics D, 2006
    Co-Authors: C P Singh, Suresh Kumar
    Abstract:

    A special law of variation for Hubble's parameter in anisotropic space–time models that yields a Constant value of the Deceleration parameter is presented. Also, a spatially homogeneous and anisotropic but locally rotationally symmetric (LRS) Bianchi type-II cosmological model is studied with a perfect fluid and Constant Deceleration parameter. Assuming the equation of state p = γρ, where 0≤γ≤1, and using a special law of variation for the Hubble parameter, we are able to construct many new solutions to Einstein's field equations of LRS Bianchi type-II for four different physical models (dust, radiation, Zel'dovich and vacuum). We discuss the solutions with power-law and exponential expansion and examine a particular class of models. A detailed study of kinematic, geometrical and observational properties is carried out.

C P Singh - One of the best experts on this subject based on the ideXlab platform.

  • anisotropic dark energy models with Constant Deceleration parameter
    General Relativity and Gravitation, 2011
    Co-Authors: Suresh Kumar, C P Singh
    Abstract:

    We consider a spatially homogeneous and totally anisotropic Bianchi-I space-time with perfect fluid (dark matter and standard visible matter) and anisotropic dark energy, which has dynamical energy density. The two sources are assumed to interact minimally and therefore their energy momentum tensors are conserved separately. Using suitable physical assumptions, the field equations are solved exactly. Various dark energy models are studied and it is found that quintessence model is suitable for describing the present evolution of the universe. The geometrical and kinematical features of the models and the behavior of the anisotropy of the dark energy, are examined in detail.

  • anisotropic bianchi type i models with Constant Deceleration parameter in general relativity
    Astrophysics and Space Science, 2007
    Co-Authors: Suresh Kumar, C P Singh
    Abstract:

    A special law of variation for Hubble’s parameter is presented in a spatially homogeneous and anisotropic Bianchi type-I space-time that yields a Constant value of Deceleration parameter. Using the law of variation for Hubble’s parameter, exact solutions of Einstein’s field equations are obtained for Bianchi-I space-time filled with perfect fluid in two different cases where the universe exhibits power-law and exponential expansion. It is found that the solutions are consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out.

  • Bianchi Type-II inflationary models with Constant Deceleration parameter in general relativity
    Pramana, 2007
    Co-Authors: C P Singh, Sushil Kumar
    Abstract:

    Einstein’s field equations are considered for a locally rotationally symmetric Bianchi Type-II space-time in the presence of a massless scalar field with a scalar potential. Exact solutions of scale factors and other physical parameters are obtained by using a special law of variation for Hubble’s parameter that yields a Constant value of Deceleration parameter. To get inflationary solutions, a flat region is considered in which the scalar potential is Constant. Power-law and exponential cases are studied and in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity. A detailed study of geometrical and kinematical properties of solutions has been carried out.

  • bianchi type ii space times with Constant Deceleration parameter in self creation cosmology
    Astrophysics and Space Science, 2007
    Co-Authors: C P Singh, Suresh Kumar
    Abstract:

    The properties of locally rotationally symmetric Bianchi type-II perfect fluid space-times are analyzed in Barber’s second self-creation theory by using a special law of variation for Hubble’s parameter that yields a Constant value of Deceleration parameter. By assuming the equation of state p=γρ, many new solutions are obtained for different era—Zel’dovich, radiation, vacuum and vacuum energy dominated. The solutions with power-law and exponential expansion are discussed. A detailed study of geometrical and physical parameters is carried out. The nature of singularity is also clarified in each case.

  • bianchi type ii cosmological models with Constant Deceleration parameter
    International Journal of Modern Physics D, 2006
    Co-Authors: C P Singh, Suresh Kumar
    Abstract:

    A special law of variation for Hubble's parameter in anisotropic space–time models that yields a Constant value of the Deceleration parameter is presented. Also, a spatially homogeneous and anisotropic but locally rotationally symmetric (LRS) Bianchi type-II cosmological model is studied with a perfect fluid and Constant Deceleration parameter. Assuming the equation of state p = γρ, where 0≤γ≤1, and using a special law of variation for the Hubble parameter, we are able to construct many new solutions to Einstein's field equations of LRS Bianchi type-II for four different physical models (dust, radiation, Zel'dovich and vacuum). We discuss the solutions with power-law and exponential expansion and examine a particular class of models. A detailed study of kinematic, geometrical and observational properties is carried out.

Tomislav Prokopec - One of the best experts on this subject based on the ideXlab platform.

  • Regulating the infrared by mode matching: a massless scalar in expanding spaces with Constant Deceleration
    Physical Review D, 2011
    Co-Authors: Tomas Janssen, Tomislav Prokopec
    Abstract:

    In this paper we consider a massless scalar field, with a possible coupling {xi} to the Ricci scalar in a D dimensional Friedmann-Lemaitre-Robertson-Walker space-time with a Constant Deceleration parameter q={epsilon}-1, {epsilon}=-H/H{sup 2}. Correlation functions for the Bunch-Davies vacuum of such a theory have long been known to be infrared divergent for a wide range of values of {epsilon}. We resolve these divergences by explicitly matching the space-time under consideration to a space-time without infrared divergencies. Such a procedure ensures that all correlation functions with respect to the vacuum in the space-time of interest are infrared finite. In this newly defined vacuum we construct the coincidence limit of the propagator and as an example calculate the expectation value of the stress-energy tensor. We find that this approach gives both in the ultraviolet and in the infrared satisfactory results. Moreover, we find that, unless the effective mass due to the coupling to the Ricci scalar {xi}R is negative, quantum contributions to the energy density always dilute away faster, or just as fast, as the background energy density. Therefore, quantum backreaction is insignificant at the one-loop order, unless {xi}R is negative. Finally we compare this approach with known results where the infrared ismore » regulated by placing the Universe in a finite box. In an accelerating universe, the results are qualitatively the same, provided one identifies the size of the Universe with the physical Hubble radius at the time of the matching. In a decelerating universe, however, the two schemes give different late time behavior for the quantum stress-energy tensor. This happens because in this case the length scale at which one regulates the infrared becomes sub-Hubble at late times.« less

  • the graviton one loop effective action in cosmological space times with Constant Deceleration
    Annals of Physics, 2010
    Co-Authors: Tomas Janssen, Tomislav Prokopec
    Abstract:

    Abstract We consider the quantum Friedmann equations which include one-loop vacuum fluctuations due to gravitons and scalar field matter in a FLRW background with Constant ϵ = - H ˙ / H 2 . After several field redefinitions, to remove the mixing between the gravitational and matter degrees of freedom, we can construct the one-loop correction to the Friedmann equations. Due to cosmological particle creation, the propagators needed in such a calculation are typically infrared divergent. In this paper we construct the graviton and matter propagators, making use of the recent construction of the infrared finite scalar propagators calculated on a compact spatial manifold in Janssen et al. (2008) [1] . The resulting correction to the Friedman equations is suppressed with respect to the tree level contribution by a factor of H 2 / m p 2 and shows no secular growth.

  • The graviton one-loop effective action in cosmological space-times with Constant Deceleration
    Annals of Physics, 2010
    Co-Authors: Tomas Janssen, Tomislav Prokopec
    Abstract:

    We consider the quantum Friedmann equations which include one-loop vacuum fluctuations due to gravitons and scalar field matter in a FLRW background with Constant $\epsilon=-{\dot{H}}/{H^2}$. After several field redefinitions, to remove the mixing between the gravitational and matter degrees of freedom, we can construct the one loop correction to the Friedmann equations. Due to cosmological particle creation, the propagators needed in such a calculation are typically infrared divergent. In this paper we construct the graviton and matter propagators, making use of the recent construction of the infrared finite scalar propagators calculated on a compact spatial manifold in \cite{Janssen:2008px}. The resulting correction to the Friedman equations is suppressed with respect to the tree level contribution by a factor of $H^2/m_p^2$ and shows no secular growth.

  • The fermion propagator in cosmological spaces with Constant Deceleration
    Classical and Quantum Gravity, 2009
    Co-Authors: Jurjen F Koksma, Tomislav Prokopec
    Abstract:

    We calculate the fermion propagator in Friedmann–Lemaˆitre–Robertson– Walker (FLRW) spacetimeswith Constant Deceleration q = −1, = −H˙ /H2 for excited states. For fermions whose mass is generated by a scalar field through a Yukawa coupling m = gYφ, we assume φ ∝α H. We first solve the mode functions by splitting the spinor into a direct product of helicity and chirality spinors. We also allow for non-vacuum states. We normalize the spinors using a consistent canonical quantization and by requiring orthogonality of particle and anti-particle spinors. We apply our propagator to calculate the one-loop effective action and renormalize using dimensional regularization. Since the Hubble parameter is now treated dynamically, this paves the way to study the dynamical backreaction of fermions on the background spacetime.

  • fermion propagator in cosmological spaces with Constant Deceleration
    arXiv: General Relativity and Quantum Cosmology, 2009
    Co-Authors: Jurjen F Koksma, Tomislav Prokopec
    Abstract:

    We calculate the fermion propagator in FLRW spacetimes with Constant Deceleration $q=\epsilon-1$, $\epsilon=-\dot{H}/H^{2}$ for excited states. For fermions whose mass is generated by a scalar field through a Yukawa coupling $m=g_{\mathrm{\scriptscriptstyle{Y}}} \phi$, we assume $\phi \propto H$. We first solve for the mode functions by splitting the spinor into a direct product of helicity and chirality spinors. We also allow for non-vacuum states. We normalise the spinors using a consistent canonical quantisation and by requiring orthogonality of particle and anti-particle spinors. We apply our propagator to calculate the one loop effective action and renormalise using dimensional regularisation. Since the Hubble parameter is now treated dynamically, this paves the way to study the dynamical backreaction of fermions on the background spacetime.

D. R. K. Reddy - One of the best experts on this subject based on the ideXlab platform.

S D Katore - One of the best experts on this subject based on the ideXlab platform.