521 research outputs found
Gravitino Production Suppressed by Dynamics of Sgoldstino
In supersymmetric theories, the gravitino is abundantly produced in the early
Universe from thermal scattering, resulting in a strong upper bound on the
reheat temperature after inflation. We point out that the gravitino problem may
be absent or very mild due to the early dynamics of a supersymmetry breaking
field, i.e. a sgoldstino. In models of low scale mediation, the field value of
the sgoldstino determines the mediation scale and is in general different in
the early Universe from the present one. A large initial field value since the
era of the inflationary reheating suppresses the gravitino production
significantly. We investigate in detail the cosmological evolution of the
sgoldstino and show that the reheat temperature may be much higher than the
conventional upper bound, restoring the compatibility with thermal
leptogenesis.Comment: 23 pages, 3 figures; v2: discussions added and one figure updated,
matches version published in JHE
Novel electronic wave interference patterns in nanographene sheets
Superperiodic patterns with a long distance in a nanographene sheet observed
by STM are discussed in terms of the interference of electronic wave functions.
The period and the amplitude of the oscillations decrease spatially in one
direction. We explain the superperiodic patterns with a static linear potential
theoretically. In the k-p model, the oscillation period decreases, and agrees
with experiments. The spatial difference of the static potential is estimated
as 1.3 eV for 200 nm in distance, and this value seems to be reasonable in
order that the potential difference remains against perturbations, for example,
by phonon fluctuations and impurity scatterings. It turns out that the
long-distance oscillations come from the band structure of the two-dimensional
graphene sheet.Comment: Published as a LETTER in J. Phys.: Condens. Matter; 8 pages; 6
figures; Online version at
http://www.iop.org/EJ/S/3/1256/0hJAmc5sCL6d.7sOO.BtLw/abstract/0953-8984/14/3
6/10
Electronic states of metallic and semiconducting carbon nanotubes with bond and site disorder
Disorder effects on the density of states in carbon nanotubes are analyzed by
a tight binding model with Gaussian bond or site disorder. Metallic armchair
and semiconducting zigzag nanotubes are investigated. In the strong disorder
limit, the conduction and valence band states merge, and a finite density of
states appears at the Fermi energy in both of metallic and semiconducting
carbon nanotubes. The bond disorder gives rise to a huge density of states at
the Fermi energy differently from that of the site disorder case. Consequences
for experiments are discussed.Comment: Phys. Rev. B: Brief Reports (to be published). Related preprints can
be found at http://www.etl.go.jp/~harigaya/NEW.htm
Lower bound of the tensor-to-scalar ratio in a nearly quadratic chaotic inflation model in supergravity
We consider an initial condition problem in a nearly quadratic chaotic
inflation model in supergravity. We introduce shift symmetry breaking not only
in the superpotential but also in the Kahler potential. In this model the
inflaton potential is nearly quadratic for inflaton field values around the
Planck scale, but deviates from the quadratic one for larger field values. As a
result, the prediction on the tensor-to-scalar ratio can be smaller than that
of a purely quadratic model. Due to the shift symmetry breaking in the Kahler
potential, the inflaton potential becomes steep for large inflaton field
values, which may prevent inflation from naturally taking place in a closed
universe. We estimate an upper bound on the magnitude of the shift symmetry
breaking so that inflation takes place before a closed universe with a Planck
length size collapses, which yields a lower bound on the tensor-to-scalar
ratio, .Comment: 11 pages, 6 figure
R-symmetric Axion/Natural Inflation in Supergravity via Deformed Moduli Dynamics
We construct a natural inflation model in supergravity where the inflaton is
identified with a modulus field possessing a shift symmetry. The superpotential
for the inflaton is generated by meson condensation due to strong dynamics with
deformed moduli constraints. In contrast to models based on gaugino
condensation, the inflaton potential is generated without -symmetry breaking
and hence does not depend on the gravitino mass. Thus, our model is compatible
with low scale supersymmetry.Comment: 15 page
Chaotic Inflation with a Fractional Power-Law Potential in Strongly Coupled Gauge Theories
Models of chaotic inflation with a fractional power-law potential are not
only viable but also testable in the foreseeable future. We show that such
models can be realized in simple strongly coupled supersymmetric gauge
theories. In these models, the energy scale during inflation is dynamically
generated by the dimensional transmutation due to the strong gauge dynamics.
Therefore, such models not only explain the origin of the fractional power in
the inflationary potential but also provide a reason why the energy scale of
inflation is much smaller than the Planck scale.Comment: 5 page
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