229,708 research outputs found
Natural Inflation with Natural Trans-Planckian Axion Decay Constant from Anomalous
We propose a natural inflation model driven by an imaginary or axionic
component of a K\"ahler modulus in string-inspired supergravity. The shift
symmetry of the axion is gauged under an anomalous symmetry, which
leads to a modulus-dependent Fayet-Iliopoulos (FI) term. The matter fields are
stabilized by F-terms, and the real component of the modulus is stabilized by
the D-term, while its axion remains light. Therefore, the masses of
real and imaginary components of the modulus are separated at different scales.
The scalar potential for natural inflation is realized by the superpotential
from the non-perturbative effects. The trans-Planckian axion decay constant,
which is needed to fit with BICEP2 observations, can be obtained naturally in
this model.Comment: 14 pages, no figure, references added, version published in JHE
Helical Phase Inflation via Non-Geometric Flux Compactifications: from Natural to Starobinsky-like Inflation
We show that a new class of helical phase inflation models can be simply
realized in minimal supergravity, wherein the inflaton is the phase component
of a complex field and its potential admits a deformed helicoid structure. We
find a new unique complex-valued index that characterizes almost the
entire region of the plane favored by new Planck observations.
Continuously varying the index , predictions interpolate from
quadratic/natural inflation parameterized by a phase/axion decay constant to
Starobinsky-like inflation parameterized by the -parameter. We
demonstrate that the simple supergravity construction realizing
Starobinsky-like inflation can be obtained from a more microscopic model by
integrating out heavy fields, and that the flat phase direction for slow-roll
inflation is protected by a mildly broken global symmetry. %, which is
mildly broken at the inflation energy scale. We study the geometrical origin of
the index , and find that it corresponds to a linear constraint relating
\kah moduli. We argue that such a linear constraint is a natural result of
moduli stabilization in Type \MyRoman{2} orientifold compactifications on
Calabi-Yau threefolds with geometric and non-geometric fluxes. Possible choices
for the index are discrete points on the complex plane that relate to
the distribution of supersymmetric Minkowski vacua on moduli space. More
precise observations of the inflationary epoch in the future may provide a
better estimation of the index . Since is determined by the fluxes
and vacuum expectation values of complex structure moduli, such observations
would characterize the geometry of the internal space as well.Comment: 26 pages, 4 figures; 4+1 figure, discussion on several energy scales
added, references added, to appear in JHE
The influence of reconstruction criteria on the sensitive probes of the symmetry potential
Different criteria of constructing clusters and tracing back
resonances from the intermediate-energy neutron-rich HICs are discussed by
employing the updated UrQMD transport model. It is found that both the
phase-space and the coordinate-density criteria affect the single and the
double neutron/proton ratios of free nucleons at small transverse momenta, but
the influence becomes invisible at large transverse momenta. The effect of
different methods of reconstructing freeze-out s on the
ratio is strong in a large kinetic energy region.Comment: 8 pages, 7 fig
Aligned Natural Inflation and Moduli Stabilization from Anomalous Gauge Symmetries
To obtain natural inflation with large tensor-to-scalar ratio in string
framework, we need a special moduli stabilization mechanism which can separate
the masses of real and imaginary components of K\"ahler moduli at different
scales, and achieve a trans-Planckian axion decay constant from sub-Planckian
axion decay constants. In this work, we stabilize the matter fields by F-terms
and the real components of K\"ahler moduli by D-terms of two anomalous
symmetries strongly at high scales, while the
corresponding axions remain light due to their independence on the
Fayet-Iliopoulos (FI) term in moduli stabilization. The racetrack-type axion
superpotential is obtained from gaugino condensations of the hidden gauge
symmetries with massive matter fields in the bi-fundamental
respresentations. The axion alignment via Kim-Nilles-Pelroso (KNP) mechanism
corresponds to an approximate exchange symmetry of two K\"ahler moduli in
our model, and a slightly symmetry breaking leads to the natural
inflation with super-Planckian decay constant.Comment: 17 pages, no figur
Helical Phase Inflation
We show that the quadratic inflation can be realized by the phase of a
complex field with helicoid potential. Remarkably, this helicoid potential can
be simply realized in minimal supergravity. The global symmetry of the
K\"ahler potential introduces a flat direction and evades the problem
automatically. So such inflation is technically natural. The phase excursion is
super-Planckian as required by the Lyth bound, while the norm of the complex
field can be suppressed in the sub-Planckian region. This model resolves the
ultraviolet sensitive problem of the large field inflation, besides, it also
provides a new type of monodromy inflation in supersymmetric field theory with
consistent field stabilization.Comment: 4 pages+references, 2 figures, phase monodromy in supersymmetric
field theory is adde
Cosmological evolution of a D-brane
We study the cosmological evolution of a single BPS D-brane in the absence of
potential, which is in the category of the Chaplygin gas cosmological model.
When such a D-brane coupled to gravity moves in the bulk with a non-vanishing
velocity, it tends to slow down to zero velocity via mechanisms like
gravitational waves leakage to the bulk, losing its kinetic energy to fuel the
expansion of the universe on the D-brane. If the initial velocity of the
D-brane is high enough, the universe on the D-brane undergoes a dust-like stage
at early times and an acceleration stage at late times, as observed in the
original Chaplygin gas model. When the D-brane velocity is initially zero, the
D-brane will always remain fixed at some position in the bulk, with the brane
tension over the Plank mass squared as a cosmological constant. Interestingly,
this kind of fixed brane universe can arise as defects from tachyon inflation
on a non-BPS D-brane with one dimension higherWe study the cosmological
evolution of a single BPS D-brane coupled to gravity in the absence of
potential. When such a D-brane moves in the bulk with non-vanishing velocity,
it tends to slow down to zero velocity via mechanisms like gravitational wave
leakage to the bulk, losing its kinetic energy to fuel the expansion of the
universe on the D-brane. If the initial velocity of the D-brane is high enough,
the universe on the D-brane undergoes a dust-like stage at early times and an
acceleration stage at late times, realising the original Chaplygin gas model.
When the D-brane velocity is initially zero, the D-brane will always remain
fixed at some position in the bulk, with the brane tension over the Plank mass
squared as a cosmological constant. It is further shown that this kind of fixed
brane universe can arise as defects from tachyon inflation on a non-BPS D-brane
with one dimension higher.Comment: 13 page
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