4,818 research outputs found
Inflation and dark energy arising from geometrical tachyons
We study the motion of a BPS D3-brane in the NS5-brane ring background. The
radion field becomes tachyonic in this geometrical set up. We investigate the
potential of this geometrical tachyon in the cosmological scenario for
inflation as well as dark energy. We evaluate the spectra of scalar and tensor
perturbations generated during tachyon inflation and show that this model is
compatible with recent observations of Cosmic Microwave Background (CMB) due to
an extra freedom of the number of NS5-branes. It is not possible to explain the
origin of both inflation and dark energy by using a single tachyon field, since
the energy density at the potential minimum is not negligibly small because of
the amplitude of scalar perturbations set by CMB anisotropies. However
geometrical tachyon can account for dark energy when the number of NS5-branes
is large, provided that inflation is realized by another scalar field.Comment: 11 pages, 8 figure
Hot Nuclear Matter : A Variational Approach
We develop a nonperturbative technique in field theory to study properties of
infinite nuclear matter at zero temperature as well as at finite temperatures.
Here we dress the nuclear matter with off-mass shell pions. The techniques of
thermofield dynamics are used for finite temperature calculations. Equation of
state is derived from the dynamics of the interacting system in a self
consistent manner. The transition temperature for nuclear matter appears to be
around 15 MeV.Comment: 16 pages, IP/BBSR/91-3
Neutron matter - Quark matter phase transition and Quark star
We consider the neutron matter quark matter phase transition along with
possible existence of hybrid quark stars. The equation of state for neutron
matter is obtained using a nonperturbative method with pion dressing of the
neutron matter and an analysis similar to that of symmetric nuclear matter. The
quark matter sector is treated perturbatively in the small distance domain. For
bag constant =148 MeV, a first order phase transition is seen. In the
context of neutron quark hybrid stars, Tolman-Oppenheimer-Volkoff equations are
solved using the equations of state for quark matter and for neutron matter
with a phase transition as noted earlier. Stable solutions for such stars are
obtained with the Chandrasekhar limit as 1.58 and radius around 10
km. The bulk of the star is quark matter with a thin crust of neutron matter of
less than a kilometer.Comment: 28 pages including 9 figures, Revtex, IP/BBSR/92-8
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