15 research outputs found
Leptogenesis from Gravity Waves in Models of Inflation
We present a new mechanism for creating the observed cosmic matter-antimatter
asymmetry which satisfies all three Sakharov conditions from one common thread,
gravitational waves. We generate lepton number through the gravitational
anomaly in the lepton number current. The source term comes from elliptically
polarizated gravity waves that are produced during inflation if the inflaton
field contains a CP-odd component. In simple inflationary scenarios, the
generated matter asymmetry is very small. We describe some special conditions
in which our mechanism can give a matter asymmetry of realistic size.Comment: 4 pages, RevTeX4.1 format; an error in computations correcte
Can the string scale be related to the cosmic baryon asymmetry?
In a previous work, a mechanism was presented by which baryon asymmetry can
be generated during inflation from elliptically polarized gravitons.
Nonetheless, the mechanism only generated a realistic baryon asymmetry under
special circumstances which requires an enhancement of the lepton number from
an unspecified GUT. In this note we provide a stringy embedding of this
mechanism through the Green-Schwarz mechanism, demonstrating that if the
model-independent axion is the source of the gravitational waves responsible
for the lepton asymmetry, one can observationally constrain the string scale
and coupling.Comment: 12 Pages, typo corrected in the tex
Brane Gas Cosmology, M-theory and Little String Theory
We generalize the Brane Gas Cosmological Scenario to M-theory degrees of
freedom, namely and branes. Without brane intersections, the
Brandenberger Vafa(BV) arguments applied to M-theory degrees of freedom
generically predict a large 6 dimensional spacetime. We show that intersections
of and branes can instead lead to a large 4 dimensional spacetime.
One dimensional intersections in 11D is related to (2,0) little strings (LST)
on NS5 branes in type IIA. The gas regime of membranes in M-theory corresponds
to the thermodynamics of LST obtained from holography. We propose a mechanism
whereby LST living on the worldvolume of NS5 (M5)-branes wrapping a five
dimensional torus, annihilate most efficiently in 3+1 dimensions leading to a
large 3+1 dimensional spacetime. We also show that this picture is consistent
with the gas approximation in M-theory.Comment: 8 page
A thermal instability for positive brane cosmological constant in the Randall-Sundrum cosmologies
We describe a novel dynamical mechanism to radiate away a positive four
dimensional cosmological constant, in the Randall-Sundrum cosmological
scenario. We show that there are modes of the bulk gravitational field for
which the brane is effectively a mirror. This will generally give rise to an
emission of thermal radiation from the brane into the bulk. The temperature
turns out to be nonvanishing only if the effective four dimensional
cosmological constant is positive. In any theory where the four dimensional
vacuum energy is a function of physical degrees of freedom, there is then a
mechanism that radiates away any positive four dimensional cosmological
constant.Comment: 14 pages. The discussion on the relation between temperature and
effective 4d cosmological constant is changed. References are adde