arXiv subjects

M. R. Tanhayi

Publications and source records attributed to M. R. Tanhayi.

8 recordsLinked to original sources

arXiv2016

Inflation in Non-de Sitter Background with Coherent States

We use the excited coherent states built over the initial non-de Sitter modes, to study the modification of spectra of primordial scalar fluctuation. Non-de Sitter modes are actually the asymptotic solution of the inflaton field equation[JHEP 09(2014) 020]. We build excited coherent states over the non-de Sitter modes and despite the lack of interactions in the Lagrangian, we find a non-zero one-point function. It is shown that the primordial non-Gaussianity resulting from excited-de Sitter modes depend both of time and background space-time. It is very tiny of order $(\leq{10}^{-24})$, at the Planck initial fixed time that confirmed by resent observations for single field inflation but it grows in the present epoch. Moreover, our results at the leading order are similar to what obtained with general initial states and in the dS limit leads to standard results [JCAP 1202(2012) 005]. We will show that the non-dS modes and its resulting spectrum are more usable for far past time limit.

gr-qc↗

arXiv2014

Power Spectrum with Auxiliary Fields in de Sitter Space

We use the auxiliary fields and (excited-) de Sitter solutions to study the standard power spectrum of primordial fluctuations of a scalar field in the early universe. The auxiliary fields are the negative norm solutions of the field equation and as it is shown, with a fixed boundary condition, utilizing these states results in a finite power spectrum without any infinity. The power spectrum is determined by the de Sitter solutions up to some corrections and the space-time symmetry is not broken in this point of view. The modulation to the power spectrum is of order $ (\frac{H}Λ)^{2} $, where $ H $ is the Hubble parameter and $ Λ$ is the energy scale, e.g., Planck scale.

hep-th↗

arXiv2013

Weyl-invariant extension of the Metric-Affine Gravity

Metric-affine geometry provides a non-trivial extension of the general relativity where the metric and connection are treated as the two independent fundamental quantities in constructing the space-time (with non-vanishing torsion and non-metricity). In this paper we study the generic form of action in this formalism, and then construct the Weyl-invariant version of this theory. It is shown that in Weitzenbock space, the obtained Weyl-invariant action can cover the conformally invariant teleparallel action. Finally the related field equations are obtained in the general case.

gr-qc↗

arXiv2012

Radiation effects on particle's trajectory in the linear level

In this work, we first obtain the linear form of the scalar self-force and then, the effect of self-force on the particle's trajectory is considered. In de Sitter space-time, within the classical approach, we consider this effect. Finally, some limits for the problem are presented.

gr-qc↗

arXiv2011

Auxiliary "massless" spin-2 field in de Sitter universe

For the tensor field of rank-2 there are two unitary irreducible representation (UIR) in de Sitter (dS) space denoted by $Π^{\pm}_{2,2}$ and $Π^{\pm}_{2,1}$ [1]. In the flat limit only the $Π^{\pm}_{2,2}$ coincides to the UIR of Poincaré group, the second one becomes important in the study of conformal gravity. In the pervious work, Dirac's six-cone formalism has been utilized to obtain conformally invariant (CI) field equation for the "massless" spin-2 field in dS space [2]. This equation results in a field which transformed according to $Π^{\pm}_{2,1}$, we name this field the auxiliary field. In this paper this auxiliary field is considered and also related two-point function is calculated as a product of a polarization tensor and "massless" conformally coupled scalar field. This two-point function is de Sitter invariant.

gr-qc↗

arXiv2010

Linear Weyl Gravity in de Sitter Universe

In this paper we obtain the linear Weyl gravity in de Sitter background. Its linear form in five-dimensional ambient space notation has also been obtained. From the group theoretical point of view, we show that this conformal invariant fourth order theory in its linear form does not transform as an unitary irreducible representation of the de Sitter group.

gr-qc↗

arXiv2010

Conformal linear gravity in de Sitter space

It has been shown that the theory of linear conformal quantum gravity must include a tensor field of rank-3 and mixed symmetry [1]. In this paper, we obtain the corresponding field equation in de Sitter space. Then, in order to relate this field with the symmetric tensor field of rank-2, $\K_{αβ}$ related to graviton, we will define homomorphisms between them. Our main result is that if one insists $\K_{αβ}$ to be a unitary irreducible representation of de Sitter and conformal groups it must satisfy a filed equation of order 6, which is obtained.

gr-qc↗

arXiv2008

Conformally Invariant "Massless" Spin-2 Field in de Sitter Universe

''Massless'' spin-2 field equation in de Sitter space, which is invariant under the conformal transformation, has been obtained. The frame work utilized is the symmetric rank-2 tensor field of the conformal group. Our method is based on the group theoretical approach and six-cone formalism, initially introduced by Dirac. Dirac's six-cone is used to obtain conformally invariant equations on de Sitter space. The solution of the physical sector of massless spin-2 field (linear gravity) in de Sitter ambient space is written as a product of a generalized polarization tensor and a massless minimally coupled scalar field. Similar to the minimally coupled scalar field, for quantization of this sector, the Krein space quantization is utilized. We have calculated the physical part of the linear graviton two-point function. This two-point function is de Sitter invariant and free of pathological large distance behavior.

gr-qc↗