Searcharxiv⌕ Search

arXiv subjects

Forough Nasseri

Publications and source records attributed to Forough Nasseri.

At least 19 recordsLinked to original sources
arXiv2007

Time variation of the gravitational coupling constant in decrumpling cosmology

Within the framework of a model universe with time variable space dimension (TVSD) model, known as decrumpling or TVSD model, we study the time variation of the gravitational coupling constant. Using observational bounds on the present time variation of the gravitational Newton's constant in three-dimensional space we are able to obtain a constraint on the time variation of the gravitational coupling constant. As a result, the absolute value of the time variation of the gravitational coupling constant must be less than $\sim 10^{-11} {\rm yr}^{-1}$.

hep-th↗
arXiv2007

Time variation of the gravitational coupling constant in all dimensions: Kasner-type cosmological models

We formulate the time variation of the gravitational coupling constant in all dimensions. We show that the time variation of the gravitational coupling constant is related to the time variation of the Newton's constant in three-space dimensions and also is related to the time variation of the volume of the extra spatial dimensions. Our results here are based on a model-independent approach. We then study time variation of the gravitational coupling constant in Kasner-type cosmological models. In the case of $(4+1)$-dimensional spacetime we show that the gravitational coupling constant decreases within the cosmic time and the rate of its time variabilty is of the order of the inverse of the present value of the age of the universe.

hep-th↗
arXiv2006

The Event Horizon of The Schwarzschild Black Hole in Noncommutative Spaces

The event horizon of Schwarzschild black hole is obtained in noncommutative spaces up to the second order of perturbative calculations. Because this type of black hole is non-rotating, to the first order there is no any effect on the event horizon due to the noncommutativity of space. A lower limit for the noncommutativity parameter is also obtained. As a result, the event horizon in noncommutative spaces is less than the event horizon in commutative spaces.

hep-th↗
arXiv2006

Time variation of the fine structure constant in decrumpling or TVSD model

Within the framework of a model universe with time variable space dimension (TVSD), known as decrumpling or TVSD model, we study the time variation of the fine structure constant. Using observational bounds on the present time variation of the fine structure constant, we are able to obtain the present time variation of spatial dimensions.

hep-th↗
arXiv2006

Decrumpling or TVSD model explains why the universe is accelerating today

Within the framework of a model universe with time variable space dimension (TVSD), known as decrumpling or TVSD model, we show the present value of the deceleration parameter is negative implying that the universe is accelerating today. Our study is based on a flat universe with the equation of state parameter to be $ω(z=0) \approx -1$ today. More clearly, decrumpling model tells us the universe is accelerating today due to the cosmological constant which is the simplest candidate for the dark energy.

hep-th↗
arXiv2005

Schwarzschild Black Hole in Noncommutative Spaces

We study the effects of noncommutative spaces on the horizon, the area spectrum and Hawking temperature of a Schwarzschild black hole. The results show deviations from the usual horizon, area spectrum and the Hawking temperature. The deviations depend on the parameter of space-space noncommutativity.

hep-th↗
arXiv2005

Dynamics of inflationary cosmology in TVSD model

Within the framework of a model Universe with time variable space dimensions (TVSD), known as decrumpling or TVSD model, we study TVSD chaotic inflation and obtain dynamics of the inflaton, scale factor and spatial dimension. We also study the quantum fluctuations of the inflaton field and obtain the spectral index and its running in this model. Two classes of examples have been studied and comparisons made with the standard slow-roll formulae. We compare our results with the recent Wilkinson Microwave Anisotropy Probe (WMAP) data.

astro-ph↗
arXiv2005

Limits on the Time Evolution of Space Dimensions from Newton's Constant

Limits are imposed upon the possible rate of change of extra spatial dimensions in a decrumpling model Universe with time variable spatial dimensions (TVSD) by considering the time variation of (1+3)-dimensional Newton's constant. Previous studies on the time variation of (1+3)-dimensional Newton's constant in TVSD theory had not been included the effects of the volume of the extra dimensions and the effects of the surface area of the unit sphere in D-space dimensions. Our main result is that the absolute value of the present rate of change of spatial dimensions to be less than about 10^{-14}yr^{-1}. Our results would appear to provide a prima facie case for ruling the TVSD model out. We show that based on observational bounds on the present-day variation of Newton's constant, one would have to conclude that the spatial dimension of the Universe when the Universe was at the Planck scale to be less than or equal to 3.09. If the dimension of space when the Universe was at the Planck scale is constrained to be fractional and very close to 3, then the whole edifice of TVSD model loses credibility.

hep-th↗
arXiv2004

Running of the Spectral Index in Noncommutative Inflation

We study the cosmological implications of the space-space noncommutative inflation and present formulae for the spectral index and its running. Our results show that deviations from the spectral index and its running depend on the space-space noncommutativity length scale. We conclude that in the slow-roll regime of a typical inflationary scenario, space-space noncommutativity has negligible effects on both the spectral index and its running. Two classes of examples have been studied and comparisons made with the standard slow-roll formulae. The results show that the correction terms to the commutative case are positive for the spectral index and negative for the running of the spectral index. Nevertheless the spectral index in noncommutative spaces is less than one owing to the very small values of the correction terms.

astro-ph↗
arXiv2004

Noncommutative Decrumpling Inflation and Running of the Spectral Index

We present a new inflation model, known as noncommutative decrumpling inflation, in which space has noncommutative geometry with time variability of the number of spatial dimensions. Within the framework of noncommutative decrumpling inflation, we compute both the spectral index and its running. Our results show that the effects of both time variability of the number of spatial dimensions and noncommutative geometry on the spectral index and its running. Two classes of examples have been studied and comparisons made with the standard slow-roll formulae. We conclude that the effects of noncommutative geometry on the spectral index and its running are much smaller than the effects of time variability of spatial dimensions.

hep-th↗
arXiv2002

Dynamics of Chaotic Inflation with Variable Space Dimension

Within the framework of a model Universe with variable space dimension, we study chaotic inflation with the potential $m^2ϕ^2/2$, and calculate the dynamical solutions of the inflaton field, variable space dimension, scale factor, and their interdependence during the inflationary epoch. We show that the characteristic of the variability of the space dimension causes the inflationary epoch in the variable space dimension to last longer than the inflationary epoch in the constant space dimension.

gr-qc↗
arXiv2001

Chaotic Inflation with Time-Variable Space Dimensions

Assuming the space dimension is not constant but decreases during the expansion of the Universe, we study chaotic inflation with the potential $m^2ϕ^2/2$. Our investigations are based on a model Universe with variable space dimensions. We write down field equations in the slow-roll approximation, and define slow-roll parameters by assuming the number of space dimensions decreases continuously as the Universe expands. The dynamical character of the space dimension shifts the initial and final value of the inflaton field to larger values. We obtain an upper limit for the space dimension at the Planck length. This result is in agreement with previous works for the effective time variation of the Newtonian gravitational constant in a model Universe with variable space dimensions.

gr-qc↗