Blue Spectra of Kalb-Ramond Axions and Fully Anisotropic String Cosmologies

Abstract

The inhomogeneities associated with massless Kalb-Ramond axions can be amplified not only in isotropic (four-dimensional) string cosmological models but also in the fully anisotropic case. If the background geometry is isotropic, the axions (which are not part of the homogeneous background) develop, outside the horizon, growing modes leading, ultimately, to logarithmic energy spectra which are "red" in frequency and increase at large distance scales. We show that this conclusion can be evaded not only in the case of higher dimensional backgrounds with contracting internal dimensions but also in the case of string cosmological scenarios which are completely anisotropic in four dimensions. In this case the logarithmic energy spectra turn out to be "blue" in frequency and, consequently, decreasing at large distance scales. We elaborate on anisotropic dilaton-driven models and we argue that, incidentally, the background models leading to (or flat) logarithmic energy spectra for axionic fluctuations are likely to be isotropized by the effect of string tension corrections.

17 pages in LaTex style, 8 Encapsulated figures

References in corpus (9)

• Vacuum fluctuations in axion-dilaton cosmologies
• Inhomogeneous Pre-Big Bang String Cosmology
• Tensor perturbations in high-curvature string backgrounds
• Cosmic microwave background polarization, Faraday rotation and stochastic gravity-waves backgrounds
• Seeds of large-scale anisotropy in string cosmology
• Massless (pseudo-)scalar seeds of CMB anisotropy
• A numerical simulation of pre-big bang cosmology
• Regular Cosmological Examples of Tree-Level Dilaton-Driven Models
• Singularity free dilaton-driven cosmologies and pre-little-bang

Cited by in corpus (15)

• The Pre-Big Bang Scenario in String Cosmology
• Superstring Cosmology
• Static spherisymmetric solutions, gravitational lensing and perihelion precession in Einstein--Kalb--Ramond theory
• Constraints on pre-big bang parameter space from CMBR anisotropies
• Quintessential perturbations during scaling regime
• A singularity theorem based on spatial averages
• Hypermagnetic gyrotropy, inflation and the baryon asymmetry of the Universe
• Homogeneous magnetic fields in fully anisotropic string cosmological backgrounds
• No-hair conjectures, primordial shear and protoinflationary initial conditions
• Minimal coupling of the Kalb-Ramond field to a scalar field
• Does curvature-dilaton coupling with Kalb Ramond field lead to an accelerating Universe ?
• Kalb-Ramond axion production in anisotropic string cosmologies
• Cold and Hot Dark Matter from a Single Nonthermal Relic
• Spherically symmetric solution in a space-time with torsion
• Quantum Kalb-Ramond Field in D-dimensional de Sitter Spacetimes