1,022 research outputs found
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
Scattering of cosmic strings by black holes: loop formation
We study the deformation of a long cosmic string by a nearby rotating black
hole. We examine whether the deformation of a cosmic string, induced by the
gravitational field of a Kerr black hole, may lead to the formation of a loop
of cosmic string. The segment of the string which enters the ergosphere of a
rotating black hole gets deformed and, if it is sufficiently twisted, it can
self-intersect chopping off a loop of cosmic string. We find that the formation
of a loop, via this mechanism, is a rare event. It will only arise in a small
region of the collision phase space, which depends on the string velocity, the
impact parameter and the black hole angular momentum. We conclude that
generically, the cosmic string is simply scattered or captured by the rotating
black hole.Comment: 11 pages, 2 figures, RevTe
Les transferts de revenus des migrants : quel impact sur le dĂ©veloppement Ă©conomique et financier des pays dâAfrique subsaharienne ?
Les revenus des migrants peuvent agir sur la croissance et le dĂ©veloppement financier des Ă©conomies bĂ©nĂ©ficiaires, notamment dâAfrique, sous rĂ©serve dâune formalisation accrue des circuits de transferts et de la mise en oeuvre de rĂ©formes structurelles ciblĂ©es dans les pays rĂ©cepteurs.Afrique subsaharienne, croissance, financement du dĂ©veloppement, secteur financier, transferts des migrants.
D-term inflation in non-minimal supergravity
D-term inflation is one of the most interesting and versatile models of
inflation. It is possible to implement naturally D-term inflation within high
energy physics, as for example SUSY GUTs, SUGRA, or string theories. D-term
inflation avoids the -problem, while in its standard form it always ends
with the formation of cosmic strings. Given the recent three-year WMAP data on
the cosmic microwave background temperature anisotropies, we examine whether
D-term inflation can be successfully implemented in non-minimal supergravity
theories. We show that for all our choices of K\"ahler potential, there exists
a parameter space for which the predictions of D-term inflation are in
agreement with the measurements. The cosmic string contribution on the measured
temperature anisotropies is always dominant, unless the superpotential coupling
constant is fine tuned; a result already obtained for D-term inflation within
minimal supergravity. In conclusion, cosmic strings and their r\^ole in the
angular power spectrum cannot be easily hidden by just considering a non-flat
K\"ahler geometry.Comment: 29 pages, 9 figures; minor changes to match publihed versio
Mesenchymal Stromal Cells Impair the Differentiation of CD14++CD16-CD64+ Classical Monocytes into CD14++CD16+CD64++ Activate Monocytes
Production of topological defects at the end of inflation
Hybrid inflation within supersymmetric grand unified theories, as well as
inflation through brane collisions within braneworld cosmological models, lead
to the formation of one-dimensional defects. Observational data, mainly from
the cosmic microwave background temperature anisotropies but also from the
gravitational wave background, impose constraints on the free parameters of the
models. I review these inflationary models and discuss the constraints from the
currently available data.Comment: 9 pages, Invited talk in the Conference "Challenges in Particle
Astrophysics" -- 6th Rencontres du Vietnam, Hanoi (Vietnam) 6-12 Aug. 200
Hybrid inflation followed by modular inflation
Inflationary models with a superheavy scale F-term hybrid inflation followed
by an intermediate scale modular inflation are considered. The restrictions on
the power spectrum P_R of curvature perturbation and the spectral index n_s
from the recent data within the power-law cosmological model with cold dark
matter and a cosmological constant can be met provided that the number of
e-foldings N_HI* suffered by the pivot scale k_*=0.002/Mpc during hybrid
inflation is suitably restricted. The additional e-foldings needed for solving
the horizon and flatness problems are generated by modular inflation with a
string axion as inflaton. For central values of P_R and n_s, the grand
unification scale comes out, in the case of standard hybrid inflation, close to
its supersymmetric value M_GUT=2.86 x 10^16 GeV, the relevant coupling constant
is relatively large (0.005-0.14), and N_HI* is between 10 and 21.7. In the
shifted [smooth] hybrid inflation case, the grand unification scale can be
identified with M_GUT for N_HI*=21 [N_HI*=18].Comment: 13 pages including 3 figures, uses ws-ijmpa.cls, minor corrections
included, talk given at the CTP Symposium on Supersymmetry at LHC:
Theoretical and Experimental Perspectives, British University in Egypt (BUE),
Cairo, 11-14 March 2007 (to appear in the proceedings
A new high performance liquid chromatographic technique for separation and determination of adenylic and nicotinamide nucleotides in Lactobacillus plantarum
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