1,873 research outputs found
Heterotic Cosmic Strings
We show that all three conditions for the cosmological relevance of heterotic
cosmic strings, the right tension, stability and a production mechanism at the
end of inflation, can be met in the strongly coupled M-theory regime. Whereas
cosmic strings generated from weakly coupled heterotic strings have the well
known problems posed by Witten in 1985, we show that strings arising from
M5-branes wrapped around 4-cycles (divisors) of a Calabi-Yau in heterotic
M-theory compactifications, solve these problems in an elegant fashion.Comment: 25 pages, v2: section and references adde
Phases of N=1 USp(2N_c) Gauge Theories with Flavors
We studied the phase structures of N=1 supersymmetric USp(2N_c) gauge theory
with N_f flavors in the fundamental representation as we deformed the N=2
supersymmetric QCD by adding the superpotential for adjoint chiral scalar
field. We determined the most general factorization curves for various breaking
patterns, for example, the two different breaking patterns of quartic
superpotential. We observed all kinds of smooth transitions for quartic
superpotential. Finally we discuss the intriguing role of USp(0) in the phase
structure and the possible connection with observations made recently in
hep-th/0304271 (Aganagic, Intriligator, Vafa and Warner) and in hep-th/0307063
(Cachazo).Comment: 61pp; Improved the presentation, references are added and to appear
in PR
A ferromagnet with a glass transition
We introduce a finite-connectivity ferromagnetic model with a three-spin
interaction which has a crystalline (ferromagnetic) phase as well as a glass
phase. The model is not frustrated, it has a ferromagnetic equilibrium phase at
low temperature which is not reached dynamically in a quench from the
high-temperature phase. Instead it shows a glass transition which can be
studied in detail by a one step replica-symmetry broken calculation. This spin
model exhibits the main properties of the structural glass transition at a
solvable mean-field level.Comment: 7 pages, 2 figures, uses epl.cls (included
A Century of Cosmology
In the century since Einstein's anno mirabilis of 1905, our concept of the
Universe has expanded from Kapteyn's flattened disk of stars only 10 kpc across
to an observed horizon about 30 Gpc across that is only a tiny fraction of an
immensely large inflated bubble. The expansion of our knowledge about the
Universe, both in the types of data and the sheer quantity of data, has been
just as dramatic. This talk will summarize this century of progress and our
current understanding of the cosmos.Comment: Talk presented at the "Relativistic Astrophysics and Cosmology -
Einstein's Legacy" meeting in Munich, Nov 2005. Proceedings will be published
in the Springer-Verlag "ESO Astrophysics Symposia" series. 10 pages Latex
with 2 figure
Influence of the in-medium pion dispersion relation in heavy ion collisions
We investigate the influence of medium corrections to the pion dispersion
relation on the pion dynamics in intermediate energy heavy ion collisions. To
do so a pion potential is extracted from the in-medium dispersion relation and
used in QMD calculations and thus we take care of both, real and imaginary part
of the pion optical potential. The potentials are determined from different
sources, i.e. from the --hole model and from phenomenological
approaches. Depending on the strength of the potential a reduction of the
anti-correlation of pion and nucleon flow in non-central collisions is observed
as well as an enhancement of the high energetic yield in transverse pion
spectra. A comparison to experiments, in particular to -spectra for the
reaction Ca+Ca at 1 GeV/nucleon and the pion in-plane flow in Ne+Pb collisions
at 800 MeV/nucleon, generally favours a weak potential.Comment: 25 pages, using REVTeX, 6 postscript figures; replaced by published
versio
Multiple-Surrogate Approach to Helicopter Rotor Blade Vibration Reduction
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77383/1/AIAA-40291-933.pd
Cauchy Horizons, Thermodynamics and Closed Time-like Curves in Planar Supersymmetric Space-times
We study geodesically complete, singularity free space-times induced by
supersymmetric planar domain walls interpolating between Minkowski and anti-de
Sitter () vacua. A geodesically complete space-time without closed
time-like curves includes an infinite number of semi-infinite Minkowski
space-times, separated from each other by a region of space-time. These
space-times are closely related to the extreme Reissner Nordstr\" om (RN) black
hole, exhibiting Cauchy horizons with zero Hawking temperature, but in contrast
to the RN black hole there is no entropy. Another geodesically complete
extension with closed time-like curves involves space-times connecting a finite
number of semi-infinite Minkowski space-times.Comment: 11 pages, 1 figure appended, phyzz
Second order perturbations of a zero-pressure cosmological medium: Proofs of the relativistic-Newtonian correspondence
The dynamic world model and its linear perturbations were first studied in
Einstein's gravity. In the system without pressure the relativistic equations
coincide exactly with the later known ones in Newton's gravity. Here we prove
that, except for the gravitational wave contribution, even to the second-order
perturbations, equations for the relativistic irrotational zero-pressure fluid
in a flat Friedmann background coincide exactly with the previously known
Newtonian equations. Thus, to the second order, we correctly identify the
relativistic density and velocity perturbation variables, and we expand the
range of applicability of the Newtonian medium without pressure to all
cosmological scales including the super-horizon scale. In the relativistic
analyses, however, we do not have a relativistic variable which corresponds to
the Newtonian potential to the second order. Mixed usage of different gauge
conditions is useful to make such proofs and to examine the result with
perspective. We also present the gravitational wave equation to the second
order. Since our correspondence includes the cosmological constant, our results
are relevant to currently favoured cosmology. Our result has an important
practical implication that one can use the large-scale Newtonian numerical
simulation more reliably even as the simulation scale approaches near horizon.Comment: 10 pages, no figur
The Isotropy of Compact Universes
We discuss the problem of the stability of the isotropy of the universe in
the space of ever-expanding spatially homogeneous universes with a compact
spatial topology. The anisotropic modes which prevent isotropy being
asymptotically stable in Bianchi-type universes with non-compact
topologies are excluded by topological compactness. Bianchi type and type
universes with compact topologies must be exactly isotropic. In the
flat case we calculate the dynamical degrees of freedom of Bianchi-type and
universes with compact 3-spaces and show that type solutions
are more general than type solutions for systems with perfect fluid,
although the type models are more general than type in the vacuum
case. For particular topologies the 4-velocity of any perfect fluid is required
to be non-tilted. Various consequences for the problems of the isotropy,
homogeneity, and flatness of the universe are discussed.Comment: 22 pages in LaTeX2e with the amsmath packag
Unification, KK-thresholds and the top Yukawa coupling in F-theory GUTs
In a class of F-theory SU(5) GUTs the low energy chiral mass spectrum is
obtained from rank one fermion mass textures with a hierarchical structure
organised by U(1) symmetries embedded in the exceptional E_8 group. In these
theories chiral fields reside on matter `curves' and the tree level masses are
computed from integrals of overlapping wavefuctions of the particles at the
triple intersection points. This calculation requires knowledge of the exact
form of the wavefuctions. In this work we propose a way to obtain a reliable
estimate of the various quantities which determine the strength of the Yukawa
couplings. We use previous analysis of KK threshold effects to determine the
(ratios of) heavy mass scales of the theory which are involved in the
normalization of the wave functions. We consider similar effects from the
chiral spectrum of these models and discuss possible constraints on the
emerging matter content. In this approach, we find that the Yukawa couplings
can be determined solely from the U(1) charges of the states in the
`intersection' and the torsion which is a topological invariant quantity. We
apply the results to a viable SU(5) model with minimal spectrum which satisfies
all the constraints imposed by our analysis. We use renormalization group
analysis to estimate the top and bottom masses and find that they are in
agreement with the experimental values.Comment: 28 pages, 2 figure
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