2,427 research outputs found
Racetrack inflation and assisted moduli stabilisation
We present a model of inflation based on a racetrack model without flux
stabilization. The initial conditions are set automatically through topological
inflation. This ensures that the dilaton is not swept to weak coupling through
either thermal effects or fast roll. Including the effect of non-dilaton fields
we find that moduli provide natural candidates for the inflaton. The resulting
potential generates slow-roll inflation without the need to fine tune
parameters. The energy scale of inflation must be near the GUT scale and the
scalar density perturbation generated has a spectrum consistent with WMAP data.Comment: 17 pages, 6 figures (Latex); Error in v.1 eliminated and improved
example of modular inflation presente
Three-body confinement force in a realistic constituent quark model
We show that in realistic constituent quark models based on a two-body
confinement interaction color states appear in the middle of the experimentally
known spectrum. To avoid this situation we implement a three-body confinement
interaction, introduced on an algebraic basis, into a semirelativistic version
of the Goldstone-boson-exchange constituent quark model and by solving the
Faddeev equations we show that this interaction can increase the gap between
singlet and colour states, such as the latter can be ignored and the known
baryons can be described as systems. We analyze the effect of a -
and a Y-shape three-body interaction.Comment: 14 pages, 3 figures, revised version to appear in Nucl. Phys.
Fine-Tuning Solution for Hybrid Inflation in Dissipative Chaotic Dynamics
We study the presence of chaotic behavior in phase space in the
pre-inflationary stage of hybrid inflation models. This is closely related to
the problem of initial conditions associated to these inflationary type of
models. We then show how an expected dissipative dynamics of fields just before
the onset of inflation can solve or ease considerably the problem of initial
conditions, driving naturally the system towards inflation. The chaotic
behavior of the corresponding dynamical system is studied by the computation of
the fractal dimension of the boundary, in phase space, separating inflationary
from non-inflationary trajectories. The fractal dimension for this boundary is
determined as a function of the dissipation coefficients appearing in the
effective equations of motion for the fields.Comment: 10 pages, 4 eps figures (uses epsf), Revtex. Replaced with version to
match one in press Physical Review
Accelerating Universes in String Theory via Field Redefinition
We study cosmological solutions in the effective heterotic string theory with
-correction terms in string frame. It is pointed out that the
effective theory has an ambiguity via field redefinition and we analyze
generalized effective theories due to this ambiguity. We restrict our analysis
to the effective theories which give equations of motion of second order in the
derivatives, just as "Galileon" field theory. This class of effective actions
contains two free coupling constants. We find de Sitter solutions as well as
the power-law expanding universes in our four-dimensional Einstein frame. The
accelerated expanding universes are always the attractors in the present
dynamical system.Comment: 22 pages, 3 figures, some additional formulae adde
Can Disordered Chiral Condensates Form? A Dynamical Perspective
We address the issue of whether a region of disordered chiral condensate
(DCC), in which the chiral condensate has components along the pion
directions, can form. We consider a system going through the chiral phase
transition either via a quench, or via relaxation of the high temperature phase
to the low temperature one within a given time scale (of order ).
We use a density matrix based formalism that takes both thermal and quantum
fluctuations into account non-perturbatively to argue that if the linear
sigma model is the correct way to model the situation in QCD, then it is very
unlikely at least in the Hartree approximation, that a large ()
DCC region will form. Typical sizes of such regions are
and the density of pions in such regions is at most of order . We end with some speculations on how large DCC regions may be
formed.Comment: 21 pages LATEX, 12 figures available upon request via regular mail,
PITT-94-0
Novel ophiostomatalean fungi from galleries of Cyrtogenius africus (Scolytinae) infesting dying Euphorbia ingens
Euphorbia ingens trees have been dying in
large numbers in the Limpopo Province of South
Africa for approximately 15 years. The ambrosia
beetle Cyrtogenius africus is often found infesting
diseased and dying trees. The aim of this study was to
identify the ophiostomatoid fungi occurring in the
galleries of C. africus. Logs infested with this beetle
were collected from the KwaZulu-Natal, Limpopo,
Mpumalanga, and North West Provinces of South
Africa. Fungi belonging to the Ophiostomatales were
identified based on morphology and comparison of
sequence data for the b-tubulin, ITS1-5.8S-ITS2 and
LSU gene regions. A novel species of Ophiostoma and
a novel genus in the Ophiostomatales were identified.
Inoculation studies with these fungi produced lesions
in the branches of healthy E. ingens trees.Department of Science and Technology (DST), National Research Foundation (NRF) and DST/NRF Centre of Excellence in Tree Health Biotechnology (CTHB).http://link.springer.com/journal/104822017-04-28hb2016Forestry and Agricultural Biotechnology Institute (FABI)Microbiology and Plant Patholog
Kahler Moduli Inflation Revisited
We perform a detailed numerical analysis of inflationary solutions in Kahler
moduli of type IIB flux compactifications. We show that there are inflationary
solutions even when all the fields play an important role in the overall shape
of the scalar potential. Moreover, there exists a direction of attraction for
the inflationary trajectories that correspond to the constant volume direction.
This basin of attraction enables the system to have an island of stability in
the set of initial conditions. We provide explicit examples of these
trajectories, compute the corresponding tilt of the density perturbations power
spectrum and show that they provide a robust prediction of n_s approximately
0.96 for 60 e-folds of inflation.Comment: 27 pages, 9 figure
Thermodynamics of Large-N_f QCD at Finite Chemical Potential
We extend the previously obtained results for the thermodynamic potential of
hot QCD in the limit of large number of fermions to non-vanishing chemical
potential. We give exact results for the thermal pressure in the entire range
of temperature and chemical potential for which the presence of a Landau pole
is negligible numerically. In addition we compute linear and non-linear quark
susceptibilities at zero chemical potential, and the entropy at small
temperatures. We compare with the available perturbative results and determine
their range of applicability. Our numerical accuracy is sufficiently high to
check and verify existing results, including the recent perturbative results by
Vuorinen on quark number susceptibilities and the older results by Freedman and
McLerran on the pressure at zero temperature and high chemical potential. We
also obtain a number of perturbative coefficients at sixth order in the
coupling that have not yet been calculated analytically. In the case of both
non-zero temperature and non-zero chemical potential, we investigate the range
of validity of a scaling behaviour noticed recently in lattice calculations by
Fodor, Katz, and Szabo at moderately large chemical potential and find that it
breaks down rather abruptly at , which points to a
presumably generic obstruction for extrapolating data from small to large
chemical potential. At sufficiently small temperatures , we find
dominating non-Fermi-liquid contributions to the interaction part of the
entropy, which exhibits strong nonlinearity in the temperature and an excess
over the free-theory value.Comment: 18 pages, 7 figures, JHEP style; v2: several updates, rewritten and
extended sect. 3.4 covering now "Entropy at small temperatures and
non-Fermi-liquid behaviour"; v3: additional remarks at the end of sect. 3.4;
v4: minor corrections and additions (version to appear in JHEP
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte
Combining Anomaly and Z' Mediation of Supersymmetry Breaking
We propose a scenario in which the supersymmetry breaking effect mediated by
an additional U(1)' is comparable with that of anomaly mediation. We argue that
such a scenario can be naturally realized in a large class of models. Combining
anomaly with Z' mediation allows us to solve the tachyonic slepton problem of
the former and avoid significant fine tuning in the latter. We focus on an
NMSSM-like scenario where U(1)' gauge invariance is used to forbid a tree-level
mu term, and present concrete models, which admit successful dynamical
electroweak symmetry breaking. Gaugino masses are somewhat lighter than the
scalar masses, and the third generation squarks are lighter than the first two.
In the specific class of models under consideration, the gluino is light since
it only receives a contribution from 2-loop anomaly mediation, and it decays
dominantly into third generation quarks. Gluino production leads to distinct
LHC signals and prospects of early discovery. In addition, there is a
relatively light Z', with mass in the range of several TeV. Discovering and
studying its properties can reveal important clues about the underlying model.Comment: Minor changes: references added, typos corrected, journal versio
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