5,022 research outputs found
Constraining SUSY GUTs and Inflation with Cosmology
In the framework of Supersymmetric Grand Unified Theories (SUSY GUTs), the
universe undergoes a cascade of symmetry breakings, during which topological
defects can be formed. We address the question of the probability of cosmic
string formation after a phase of hybrid inflation within a large number of
models of SUSY GUTs in agreement with particle and cosmological data. We show
that cosmic strings are extremely generic and should be used to relate
cosmology and high energy physics. This conclusion is employed together with
the WMAP CMB data to strongly constrain SUSY hybrid inflation models. F-term
and D-term inflation are studied in the SUSY and minimal SUGRA framework. They
are both found to agree with data but suffer from fine tuning of their
superpotential coupling (\lambda \lesssim 3\times 10^(-5) or less). Mass scales
of inflation are also constrained to be less than M \lesssim 3\times 10^(15)
GeV.Comment: Based on talks given by J. Rocher at the "IAP Colloquium", Paris in
july 2004, at "COSMO 04", Toronto in September 2004, at the Workshop "Quest
For Unification", CERN in December 2004 and at the "Einstein's Century
Meeting", Paris in june 2005. To appear in the Proceedings of the "Einstein's
Century Meeting", Ed. J.-M. Alimi, A. Furzfa, AIP, Paris (2006
-term inflation, cosmic strings, and consistency with cosmic microwave background measurement
Standard D-term inflation is studied in the framework of supergravity. D-term
inflation produces cosmic strings, however it can still be compatible with CMB
measurements without invoking any new physics. The cosmic strings contribution
to the CMB data is not constant, nor dominant, contrary to some previous
results. Using current CMB measurements, the free parameters (gauge and
superpotential couplings, as well as the Fayet-Iliopoulos term) of D-term
inflation are constrained.Comment: 1 Latex file and 3 figures. accepted for publication in Physical
Review Letter
Scientific cooperation in the South China Sea: another lever for China?
Overview
Security issues in the South China Sea are often studied, whereas analysis of scientific cooperation in those waters is rare, thinly spread and short. This paper looks at shared priorities, China\u27s leading role in launching scientific programs, implications for the environment, and the use of scientific cooperation as a power vector.
The research space is increasingly well controlled, but that control isnât the product of scientific cooperation. Itâs the result of China leading research programs. Scientific cooperation hasnât reduced mistrust, and common interests donât prevail. In relations between Southeast Asia and China, the fulcrum is asymmetry. The differences in scientific cooperation noted in this paper demonstrate that asymmetry and its serious long-term consequences for neighbouring countries
Avoiding the blue spectrum and the fine-tuning of initial conditions in hybrid inflation
Hybrid inflation faces two well-known problems: the blue spectrum of the
non-supersymmetric version of the model and the fine-tuning of the initial
conditions of the fields leading to sufficient inflation to account for the
standard cosmological problems. They are investigated by studying the exact
two-fields dynamics instead of assuming slow-roll. When the field values are
restricted to be less than the reduced Planck mass, a non-negligible part of
the initial condition space (around 15% depending on potential parameters)
leads to successful inflation. Most of it is located outside the usual
inflationary valley and organized in continuous patterns instead of being
isolated as previously found. Their existence is explained and their properties
are studied. This shows that no excessive fine-tuning is required for
successful hybrid inflation. Moreover, by extending the initial condition space
to planckian-like or super-planckian values, inflation becomes generically
sufficiently long and can produce a red-tilted scalar power spectrum due to
slow-roll violations. The robustness of these properties is confirmed by
conducting our analysis on three other models of hybrid-type inflation in
various framework: "smooth" and "shifted" inflation in SUSY and SUGRA, and
"radion assisted" gauge inflation. A high percentage of successful inflation
for smooth hybrid inflation (up to 80%) is observed.Comment: 20 pages, 14 figures. Some refs added/updated. New results for Smooth
and Shifted hybrid models. To appear in PR
Genericity of Cosmic Strings Formation in SUSY GUTs
The idea of GUT implies that the universe went through a series of phase
transitions during which topological defects are expected to form. We
investigate here the genericity of cosmic strings formation in realistic SUSY
GUTs models. We conclude that all acceptable symmetry breaking schemes produce
cosmic strings after the last inflationary phase. Generically, as they form at
the end of inflation, they have a mass of order of the GUT scale. Since
cosmological data coming from CMB measurements do not show evidence for such
strings, they constrain GUT scale physics.Comment: 4 pages, talk at the XXXIX Rencontres de Moriond (La Thuile, March
2004), to appear in the proceeding
Fractal initial conditions and natural parameter values in hybrid inflation
We show that the initial field values required to produce inflation in the
two fields original hybrid model, and its supergravity F-term extension, do not
suffer from any fine-tuning problem, even when the fields are restricted to be
sub-planckian and for almost all potential parameter values. This is due to the
existence of an initial slow-roll violating evolution which has been overlooked
so far. Due to the attractor nature of the inflationary valley, these
trajectories end up producing enough accelerated expansion of the universe. By
numerically solving the full non-linear dynamics, we show that the set of such
successful initial field values is connected, of dimension two and possesses a
fractal boundary of infinite length exploring the whole field space. We then
perform a Monte-Carlo-Markov-Chain analysis of the whole parameter space
consisting of the initial field values, field velocities and potential
parameters. We give the marginalised posterior probability distributions for
each of these quantities such that the universe inflates long enough to solve
the usual cosmological problems. Inflation in the original hybrid model and its
supergravity version appears to be generic and more probable by starting
outside of the inflationary valley. Finally, the implication of our findings in
the context of the eternal inflationary scenario are discussed.Comment: 16 pages, 16 figures, uses RevTeX. Lyapunov exponents and references
added, matches published versio
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