M. Sami
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
M. Sami has a total of 4 co-authors. Here are the top co-authors by number of shared publications:
- Shinji Tsujikawa
Department of Physics, Gunma National College of Technology, Gunma 371-8530, Japan
5 shared publications - Sudhakar Panda
Harish Chandra Research Institute 211019 Allahabad India
4 shared publications - John Ward
Center for Research in String Theory Department of Physics Queen Mary University of London Mile End Road E1 4NS London UK
2 shared publications - Parampreet Singh
Louisiana State University
1 shared publication
Latest Publications
- 5 November 2007
- Published by American Physical Society (APS) in Physical Review D
- Vol. 76 (10) , 103512
Prospects of inflation in delicate D-brane cosmology
We study D-brane inflation in a warped conifold background that includes brane-position dependent corrections for the nonperturbative superpotential. Instead of stabilizing the volume modulus at instantaneous minima of the potential and studying the inflation dynamics with an effective single field (radial distance between a brane and an antibrane) , we investigate the multifield inflation scenario involving these two fields. The two-field dynamics with the potential in this model is significantly different from the effective single-field description in terms of the field when the field is integrated out. The latter picture underestimates the total number of e-foldings even by 1 order of magnitude. We show that a correct single-field description is provided by a field obtained from a rotation in the two-field space along the background trajectory. This model can give a large number of e-foldings required to solve flatness and horizon problems at the expense of fine-tunings of model parameters. We also estimate the spectra of density perturbations and show that the slow-roll parameter in terms of the rotated field determines the spectral index of scalar metric perturbations. We find that it is generally difficult to satisfy, simultaneously, both constraints of the spectral index and the cosmic background explorer normalization, while the tensor to scalar ratio is sufficiently small to match with observations.- 5 November 2007
- Published by American Physical Society (APS) in Physical Review D
- Vol. 76 (10) , 103512
Prospects of inflation in delicate D-brane cosmology
We study D-brane inflation in a warped conifold background that includes brane-position dependent corrections for the nonperturbative superpotential. Instead of stabilizing the volume modulus at instantaneous minima of the potential and studying the inflation dynamics with an effective single field (radial distance between a brane and an antibrane) , we investigate the multifield inflation scenario involving these two fields. The two-field dynamics with the potential in this model is significantly different from the effective single-field description in terms of the field when the field is integrated out. The latter picture underestimates the total number of e-foldings even by 1 order of magnitude. We show that a correct single-field description is provided by a field obtained from a rotation in the two-field space along the background trajectory. This model can give a large number of e-foldings required to solve flatness and horizon problems at the expense of fine-tunings of model parameters. We also estimate the spectra of density perturbations and show that the slow-roll parameter in terms of the rotated field determines the spectral index of scalar metric perturbations. We find that it is generally difficult to satisfy, simultaneously, both constraints of the spectral index and the cosmic background explorer normalization, while the tensor to scalar ratio is sufficiently small to match with observations.- Open Access
Prospects of inflation in delicate D-brane cosmology
We study D-brane inflation in a warped conifold background that includes brane-position dependent corrections for the nonperturbative superpotential. Instead of stabilizing the volume modulus chi at instantaneous minima of the potential and studying the inflation dynamics with an effective single field (radial distance between a brane and an anti-brane) phi, we investigate the multi-field inflation scenario involving these two fields. The two-field dynamics with the potential V(phi,chi) in this model is significantly different from the effective single-field description in terms of the field phi when the field chi is integrated out. The latter picture underestimates the total number of e-foldings even by one order of magnitude. We show that a correct single-field description is provided by a field psi obtained from a rotation in the two-field space along the background trajectory. This model can give a large number of e-foldings required to solve flatness and horizon problems at the expense of fine-tunings of model parameters. We also estimate the spectra of density perturbations and show that the slow-roll parameter eta_{psi psi}=M_{pl}^2 V_{,psi psi}/V in terms of the rotated field psi determines the spectral index of scalar metric perturbations. We find that it is generally difficult to satisfy, simultaneously, both constraints of the spectral index and the COBE normalization, while the tensor to scalar ratio is sufficiently small to match with observations.
Open AccessProspects of inflation in delicate D-brane cosmology
We study D-brane inflation in a warped conifold background that includes brane-position dependent corrections for the nonperturbative superpotential. Instead of stabilizing the volume modulus chi at instantaneous minima of the potential and studying the inflation dynamics with an effective single field (radial distance between a brane and an anti-brane) phi, we investigate the multi-field inflation scenario involving these two fields. The two-field dynamics with the potential V(phi,chi) in this model is significantly different from the effective single-field description in terms of the field phi when the field chi is integrated out. The latter picture underestimates the total number of e-foldings even by one order of magnitude. We show that a correct single-field description is provided by a field psi obtained from a rotation in the two-field space along the background trajectory. This model can give a large number of e-foldings required to solve flatness and horizon problems at the expense of fine-tunings of model parameters. We also estimate the spectra of density perturbations and show that the slow-roll parameter eta_{psi psi}=M_{pl}^2 V_{,psi psi}/V in terms of the rotated field psi determines the spectral index of scalar metric perturbations. We find that it is generally difficult to satisfy, simultaneously, both constraints of the spectral index and the COBE normalization, while the tensor to scalar ratio is sufficiently small to match with observations.
- Open Access
Avoidance of future singularities in loop quantum cosmology
We consider the fate of future singularities in the effective dynamics of loop quantum cosmology. Non-perturbative quantum geometric effects which lead to $\rho^2$ modification of the Friedmann equation at high energies result in generic resolution of singularities whenever energy density $\rho$ diverges at future singularities of Friedmann dynamics. Such quantum effects lead to the avoidance of a Big Rip, which is followed by a recollapsing universe stable against perturbations. Resolution of sudden singularity, the case when pressure diverges but energy density approaches a finite value depends on the ratio of the latter to a critical energy density of the order of Planck. If the value of this ratio is greater than unity, the universe escapes the sudden future singularity and becomes oscillatory.Open AccessAvoidance of future singularities in loop quantum cosmology
We consider the fate of future singularities in the effective dynamics of loop quantum cosmology. Non-perturbative quantum geometric effects which lead to $\rho^2$ modification of the Friedmann equation at high energies result in generic resolution of singularities whenever energy density $\rho$ diverges at future singularities of Friedmann dynamics. Such quantum effects lead to the avoidance of a Big Rip, which is followed by a recollapsing universe stable against perturbations. Resolution of sudden singularity, the case when pressure diverges but energy density approaches a finite value depends on the ratio of the latter to a critical energy density of the order of Planck. If the value of this ratio is greater than unity, the universe escapes the sudden future singularity and becomes oscillatory. - 7 April 2006
- Published by American Physical Society (APS) in Physical Review D
- Vol. 73 (8) , 083512
Inflation from D3-brane motion in the background of D5-branes
We study inflation arising from the motion of a Bogomol’nyi-Prasad-Sommerfield D3-brane in the background of a stack of parallel D5-branes. There are two scalar fields in this setup: (i) the radion field , a real scalar field, and (ii) a complex tachyonic scalar field living on the world volume of the open string stretched between the D3 and D5 branes. We find that inflation is realized by the potential of the radion field, which satisfies observational constraints coming from the cosmic microwave background. After the radion becomes of the order of the string length scale , the dynamics is governed by the potential of the complex scalar field. Since this field has a standard kinematic term, reheating can be successfully realized by the mechanism of tachyonic preheating with spontaneous symmetry breaking.- 7 April 2006
- Published by American Physical Society (APS) in Physical Review D
- Vol. 73 (8) , 083512
Inflation from D3-brane motion in the background of D5-branes
We study inflation arising from the motion of a Bogomol’nyi-Prasad-Sommerfield D3-brane in the background of a stack of parallel D5-branes. There are two scalar fields in this setup: (i) the radion field , a real scalar field, and (ii) a complex tachyonic scalar field living on the world volume of the open string stretched between the D3 and D5 branes. We find that inflation is realized by the potential of the radion field, which satisfies observational constraints coming from the cosmic microwave background. After the radion becomes of the order of the string length scale , the dynamics is governed by the potential of the complex scalar field. Since this field has a standard kinematic term, reheating can be successfully realized by the mechanism of tachyonic preheating with spontaneous symmetry breaking.- Open Access
Inflation from D3-brane motion in the background of D5-branes
We study inflation arising from the motion of a BPS D3-brane in the background of a stack of k parallel D5-branes. There are two scalar fields in this set up-- (i) the radion field R, a real scalar field, and (ii) a complex tachyonic scalar field chi living on the world volume of the open string stretched between the D3 and D5 branes. We find that inflation is realized by the potential of the radion field, which satisfies observational constraints coming from the Cosmic Microwave Background. After the radion becomes of order the string length scale l_s, the dynamics is governed by the potential of the complex scalar field. Since this field has a standard kinematic term, reheating can be successfully realized by the mechanism of tachyonic preheating with spontaneous symmetry breaking.
Open AccessInflation from D3-brane motion in the background of D5-branes
We study inflation arising from the motion of a BPS D3-brane in the background of a stack of k parallel D5-branes. There are two scalar fields in this set up-- (i) the radion field R, a real scalar field, and (ii) a complex tachyonic scalar field chi living on the world volume of the open string stretched between the D3 and D5 branes. We find that inflation is realized by the potential of the radion field, which satisfies observational constraints coming from the Cosmic Microwave Background. After the radion becomes of order the string length scale l_s, the dynamics is governed by the potential of the complex scalar field. Since this field has a standard kinematic term, reheating can be successfully realized by the mechanism of tachyonic preheating with spontaneous symmetry breaking.