828 research outputs found
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
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
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
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
Direct amine-functionalisation of Îł-Fe2O3nanoparticles
A novel and simple preparation of amine-modified Îł-Fe2O3 nanoparticles is described. The presence of amine groups on the surface, instead of hydroxyl groups, will allow conjugation of biologically active molecules to the iron oxide nanoparticles without the need for a size increasing silica shell. Furthermore, the outer amine-layer increases the temperature of the Îł-Fe2O3 to α-Fe2O3 structural transition in a similar way to previously reported cationic substitutions. This may suggest the formation of an oxideânitride outer layer. Re-dispersion of the amine-modified Îł-Fe2O3 nanoparticles led to the preparation of stable ferrofluids
Identifying eroded Messinian deposits on the Maltese Islands by gypsum Sr isotopes
International audienceEvaporite sediments are known to have formed during the Messinian high salinity crisis that has been recognized in many Mediterranean areas. This event was however never identified on the Maltese Islands. In this study, a Sr isotopic characterization of gypsum, found as secondary minerals in the Oligocene-Miocene formations of Malta and Gozo is performed. The 87Sr/86Sr values are discussed on the basis of comparison with the surrounding rock Sr isotopic signature. The data outline two distinguishable 87Sr/86Sr ratios for gypsum according to their facies. Most of crack-infilling mineral data suggest a downward fluid circulation in the Miocene sediment associated with interaction in the currently outcropping limestones. Some gypsum crystals found as crystallized spherules show significantly lower 87Sr/86Sr ratios, close to those defined in the literature for Messinian evaporate sediments. Taken together, this may suggest that an evaporate formation of Messinian age had in the past covered the present-day sedimentary sequence in Malta and Gozo
Cosmic strings and Natural Inflation
In the present work we discuss cosmic strings in natural inflation. Our
analysis is based entirely on the CMB quadrupole temperature anisotropy and on
the existing upper bound on the cosmic string tension. Our results show that
the allowed range for both parameters of the inflationary model is very
different from the range obtained recently if cosmic strings are formed at the
same time with inflation, while if strings are formed after inflation we find
that the parameters of the inflationary model are similar to the ones obtained
recently.Comment: 12 pages, 0 tables, 4 figures, accepted for publication in JHE
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
- âŠ