1,897 research outputs found
Classification and Moduli Kahler Potentials of G_2 Manifolds
Compact manifolds of G_2 holonomy may be constructed by dividing a
seven-torus by some discrete symmetry group and then blowing up the
singularities of the resulting orbifold. We classify possible group elements
that may be used in this construction and use this classification to find a set
of possible orbifold groups. We then derive the moduli Kahler potential for
M-theory on the resulting class of G_2 manifolds with blown up co-dimension
four singularities.Comment: 30 pages, Latex, references adde
G_2 Domain Walls in M-theory
M-theory is considered in its low-energy limit on a G_2 manifold with
non-vanishing flux. Using the Killing spinor equations for linear flux, an
explicit set of first-order bosonic equations for supersymmetric solutions is
found. These solutions describe a warped product of a domain wall in
four-dimensional space-time and a deformed G_2 manifold. It is shown how these
domain walls arise from the perspective of the associated four-dimensional N=1
effective supergravity theories. We also discuss the inclusion of membrane and
M5-brane sources.Comment: 30 pages, Late
Second-order perturbations of cosmological fluids: Relativistic effects of pressure, multi-component, curvature, and rotation
We present general relativistic correction terms appearing in Newton's
gravity to the second-order perturbations of cosmological fluids. In our
previous work we have shown that to the second-order perturbations, the density
and velocity perturbation equations of general relativistic zero-pressure,
irrotational, single-component fluid in a flat background coincide exactly with
the ones known in Newton's theory. Here, we present the general relativistic
second-order correction terms arising due to (i) pressure, (ii)
multi-component, (iii) background curvature, and (iv) rotation. In case of
multi-component zero-pressure, irrotational fluids under the flat background,
we effectively do not have relativistic correction terms, thus the relativistic
result again coincides with the Newtonian ones. In the other three cases we
generally have pure general relativistic correction terms. In case of pressure,
the relativistic corrections appear even in the level of background and linear
perturbation equations. In the presence of background curvature, or rotation,
pure relativistic correction terms directly appear in the Newtonian equations
of motion of density and velocity perturbations to the second order. In the
small-scale limit (far inside the horizon), relativistic equations including
the rotation coincide with the ones in Newton's gravity.Comment: 41 pages, no figur
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
Axions In String Theory
In the context of string theory, axions appear to provide the most plausible
solution of the strong CP problem. However, as has been known for a long time,
in many string-based models, the axion coupling parameter F_a is several orders
of magnitude higher than the standard cosmological bounds. We re-examine this
problem in a variety of models, showing that F_a is close to the GUT scale or
above in many models that have GUT-like phenomenology, as well as some that do
not. On the other hand, in some models with Standard Model gauge fields
supported on vanishing cycles, it is possible for F_a to be well below the GUT
scale.Comment: 62 pages, v2; references, acknowledgements and minor corrections
adde
C-axis resistivity and high Tc superconductivity
Recently we had proposed a mechanism for the normal-state C-axis resistivity
of the high-T layered cuprates that involved blocking of the
single-particle tunneling between the weakly coupled planes by strong
intra-planar electron-electron scattering. This gave a C-axis resistivity that
tracks the ab-plane T-linear resistivity, as observed in the high-temperature
limit. In this work this mechanism is examined further for its implication for
the ground-state energy and superconductivity of the layered cuprates. It is
now argued that, unlike the single-particle tunneling, the tunneling of a
boson-like pair between the planes prepared in the BCS-type coherent trial
state remains unblocked inasmuch as the latter is by construction an eigenstate
of the pair annihilation operator. The resulting pair-delocalization along the
C-axis offers energetically a comparative advantage to the paired-up trial
state, and, thus stabilizes superconductivity. In this scheme the strongly
correlated nature of the layered system enters only through the blocking
effect, namely that a given electron is effectively repeatedly monitored
(intra-planarly scattered) by the other electrons acting as an environment, on
a time-scale shorter than the inter-planar tunneling time. Possible
relationship to other inter-layer pairing mechanisms proposed by several
workers in the field is also briefly discussed.Comment: typos in equations corrected, contents unchange
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
c-axis electrodynamics of ybco
New measurements of surface impedance in ybco show that the c-axis
penetration depth and conductivity below Tc exhibit behaviour different from
that observed in the planes. The c-axis penetration depth never has the linear
temperature dependence seen in the ab-plane. Instead of the conductivity peak
seen in the planes, the c-axis microwave conductivity falls to low values in
the superconducting state, then rises slightly below 20K. These results show
that c-axis transport remains incoherent below Tc, even though this is one of
the least anisotropic cuprate superconductors.Comment: 4-page
Kaon Condensation and Dynamical Nucleons in Neutron Stars
We discuss the nature of the kaon condensation phase transition. We find
several features which, if kaons condense in neutron stars, are not only
remarkable, but must surely effect such properties as superfluidity and
transport properties, which in turn are relevant to the glitch phenomenon and
cooling rates of neutron stars. The mixed phase, because of the extensive
pressure range that it spans, will occupy a broad radial extent in a neutron
star. This region is permeated with microscopic drops (and other
configurations) located at lattice sites of one phase immersed in the
background of the other phase. The electric charge on drops is opposite to that
of the background phase {\sl and} nucleons have a mass approximately a factor
two different depending on whether they are in the drops or the background
phase. A large part of the stellar interior has this highly non-homogeneous
structure.Comment: 5 pages, 6 figures, revtex. Physical Review Letters (accepted
- …