479 research outputs found
F-enomenology
The advantages of Flipped SU(5) over conventional Supersymmetric GUTs, like
SU(5), are discussed. Recent values of the strong coupling at M_Z, sin-squared
theta-Weinberg, g-2 of the muon, and the lower limit on the proton lifetime for
the (K+, anti-neutrino) mode point directly to Flipped SU(5) as the simplest
way to avoid potential pitfalls. It is shown that "F(lipped)-enomenology"
accomodates easily all presently available low-energy data, favoring a rather
"light" supersymmetric spectrum while yielding the right amount of Cold Dark
Matter and a proton lifetime in the ((e+/muon+), pi-zero) mode which is beyond
the present experimental limit yet still possibly accessible to a further round
of experiments.Comment: 22 pages; 3 figures and 2 diagrams prepared with feynmf.mf &
feynmf.sty; Invited talk given at: 1st Intl. Conf. on String Phenomenology,
Oxford, England, July 6-11, 2002, -and- NeSS 2002, Washington D.C., USA,
September 19-21, 200
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
The march towards no-scale supergravity
The different steps that led us to the discovery of {\em no-scale supergravity} are discussed from a very personal point of view. No-scale supergravity has been heralded as the most promising effective theory that describes physics below the Planck scale. In its string-derived form it holds the potential for a Dynamical Determination Of Everything (DDOE
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
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
A No-Scale Framework for Sub-Planckian Physics
We propose a minimal model framework for physics below the Planck scale with
the following features: (i) it is based on no-scale supergravity, as favoured
in many string compactifications, (ii) it incorporates Starobinsky-like
inflation, and hence is compatible with constraints from the Planck satellite,
(iii) the inflaton may be identified with a singlet field in a see-saw model
for neutrino masses, providing an efficient scenario for reheating and
leptogenesis, (iv) supersymmetry breaking occurs with an arbitrary scale and a
cosmological constant that vanishes before radiative corrections, (v) regions
of the model parameter space are compatible with all LHC, Higgs and dark matter
constraints.Comment: 6 pages, 2 figures, some minor corrections and additions. Final
versio
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