374 research outputs found
Supercriticality of a Class of Critical String Cosmological Solutions
For a class of Friedmann-Robertson-Walker type string solutions with compact
hyperbolic spatial slices formulated in critical dimension, we find the world
sheet conformal field theory which involves the linear dilaton and
Wess-Zumino-Witten type model with the compact hyperbolic target space. By
analyzing the infrared spectrum, we conclude that the theory is actually
supercritical due to the modular invariance of string theory. Thus, taking into
account previous results, we conclude that all the simple nontrivial string
cosmological solutions are supercritical. A possible explanation of why we are
living in D=4 is provided. The interesting relation of this background with the
Supercritical String Cosmology (SSC) is pointed out
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
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 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
From Gravity to No-Scale Supergravity
We show that gravity coupled conformally to scalar fields is equivalent
to the real bosonic sector of SU(N,1)/SU(N)U(1) no-scale supergravity,
where the conformal factor can be identified with the K\"ahler potential, and
we review the construction of Starobinsky-like models of inflation within this
framework.Comment: 15 pages, version accepted for publicatio
Canonical Gauge Coupling Unification in the Standard Model with High-Scale Supersymmetry Breaking
Inspired by the string landscape and the unified gauge coupling relation in
the F-theory Grand Unified Theories (GUTs) and GUTs with suitable
high-dimensional operators, we study the canonical gauge coupling unification
and Higgs boson mass in the Standard Model (SM) with high-scale supersymmetry
breaking. In the SM with GUT-scale supersymmetry breaking, we achieve the gauge
coupling unification at about 5.3 x 10^{13} GeV, and the Higgs boson mass is
predicted to range from 130 GeV to 147 GeV. In the SM with supersymmetry
breaking scale from 10^4 GeV to 5.3 x 10^{13} GeV, gauge coupling unification
can always be realized and the corresponding GUT scale M_U is from 10^{16} GeV
to 5.3 x 10^{13} GeV, respectively. Also, we obtain the Higgs boson mass from
114.4 GeV to 147 GeV. Moreover, the discrepancies among the SM gauge couplings
at the GUT scale are less than about 4-6%. Furthermore, we present the SU(5)
and SO(10) models from the F-theory model building and orbifold constructions,
and show that we do not have the dimension-five and dimension-six proton decay
problems even if M_U \le 5 x 10^{15} GeV.Comment: RevTex4, 16 pages, 5 figures, version to appear in JHE
Starobinsky-like Inflationary Models as Avatars of No-Scale Supergravity
Models of cosmological inflation resembling the Starobinsky R + R^2 model
emerge naturally among the effective potentials derived from no-scale
SU(N,1)/SU(N) x U(1) supergravity when N > 1. We display several examples in
the SU(2,1)/SU(2) x U(1) case, in which the inflaton may be identified with
either a modulus field or a matter field. We discuss how the modulus field may
be stabilized in models in which a matter field plays the role of the inflaton.
We also discuss models that generalize the Starobinsky model but display
different relations between the tilt in the spectrum of scalar density
perturbations, n_s, the tensor-to-scalar ratio, r, and the number of e-folds,
N_*. Finally, we discuss how such models can be probed by present and future
CMB experiments.Comment: 23 pages, 3 figure
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