127 research outputs found
Supercurrent in p-wave Holographic Superconductor
The p-wave and -wave holographic superconductors with fixed DC
supercurrent are studied by introducing a non-vanishing vector potential. We
find that close to the critical temperature of zero current, the
numerical results of both the p wave model and the model are the same as
those of Ginzburg-Landau (G-L) theory, for example, the critical current and the phase transition in the presence of a DC current is
a first order transition. Besides the similar results between both models, the
superconductor shows isotropic behavior for the supercurrent, while the
p-wave superconductor shows anisotropic behavior for the supercurrent.Comment: Version 4. 18 pages, 9figures. New results of the anisotropic
behavior for the supercurrent in p-wave model added. Accepted by PR
d-wave Holographic Superconductor Vortex Lattice and Non-Abelian Holographic Superconductor Droplet
A d-wave holographic superconductor is studied under a constant magnetic
field by perturbation method, we obtain both droplet and triangular vortex
lattice solution. The results are the same as the s-wave holographic
superconductor. The non-Abelian holographic superconductor with -wave
background is also studied under magnetic field, unlike the d-wave and s-wave
models, we find that the non-Abelian model has only droplet solution.Comment: Version2, 12 pages,2 figures. Accepted by PR
One dimensional s-wave holographic superconductor with supercurrent
We study the one dimensional s-wave holographic superconductor by turning on
the vector potential in the bulk, which behaves as on the boundary. By solving the model with fixed , we
find that if we identify the with the supercurrent of the
holographic superconductor, the results agree with the Gindzburg- Landau
theory. For example, will break the superconductivity, and the
critical value of is proportional to .Comment: 13 pages, 8figures, references adde
Continuous Hawking-Page transitions in Einstein-scalar gravity
We investigate continuous Hawking-Page transitions in Einstein's gravity
coupled to a scalar field with an arbitrary potential in the weak gravity
limit. We show that this is only possible in a singular limit where the
black-hole horizon marginally traps a curvature singularity. Depending on the
subleading terms in the potential, a rich variety of continuous phase
transitions arise. Our examples include second and higher order, including the
Berezinskii-Kosterlitz-Thouless type. In the case when the scalar is dilaton,
the condition for a continuous phase transition lead to (asymptotically)
linear-dilaton background. We obtain the scaling laws of thermodynamic
functions, as well as the viscosity coefficients near the transition. In the
limit of weak gravitational interactions, the bulk viscosity asymptotes to a
universal constant, independent of the details of the scalar potential. As a
byproduct of our analysis we obtain a one-parameter family of kink solutions in
arbitrary dimension d that interpolate between AdS near the boundary and
linear-dilaton background in the deep interior. The continuous Hawking-Page
transitions found here serve as holographic models for normal-to superfluid
transitions.Comment: 35 pages + appendice
M5-branes from gauge theories on the 5-sphere
We use the 5-sphere partition functions of supersymmetric Yang-Mills theories
to explore the (2,0) superconformal theory on S^5 x S^1. The 5d theories can be
regarded as Scherk-Schwarz reductions of the 6d theory along the circle. In a
special limit, the perturbative partition function takes the form of the
Chern-Simons partition function on S^3. With a simple non-perturbative
completion, it becomes a 6d index which captures the degeneracy of a sector of
BPS states as well as the index version of the vacuum Casimir energy. The
Casimir energy exhibits the N^3 scaling at large N. The large N index for U(N)
gauge group also completely agrees with the supergravity index on AdS_7 x S^4.Comment: 44 pages, 1 figure, v4: ref added, clarified weak/strong coupling
behaviors of large N free energy, minor improvements, version to be published
in JHE
Pure Leptonic Gauge Symmetry, Neutrino Masses and Dark Matter
A possible extension of the Standard Model to include lepton number as local
gauge symmetry is investigated. In such a model, anomalies are canceled by two
extra fermions doublet. After leptonic gauge symmetry spontaneously broken,
three active neutrinos may acquire non-zero Majorana masses through the
modified Type-II seesaw mechanism. Constraints on the model from electro-weak
precision measurements are studied. Due to the discrete flavor symmetry,
right-handed Majorana neutrinos can serve as cold dark matter candidate of the
Universe. Constraint from dark matter relic abundance is calculated.Comment: 13 pages, 2 figures; typos corrected, comments and references added,
to appear in Phys. Lett.
Yukawa Textures, Neutrino Masses and Horava-Witten M-Theory
We consider the Horava-Witten based model with 5-branes situated near the
distant orbifold plane and with vanishing instanton numbers on the physical
plane. This model has a toric fibered Calabi-Yau with del Pezzo base dP_7 which
allows three generations with Standard Model gauge group at the GUT scale.
Previous analysis showed that the quark hierarchy at the electroweak scale
could be achieved qualitatively without undue fine tuning due to the effects of
the 5-branes on the Kahler potential. We extend here this analysis to include
the leptons. A new mechanism is introduced to obtain neutrino masses by
assuming massless right handed neutrinos exist in the particle spectrum, which
allows a cubic holomorphic term to exist in the Kahler metric, l_L*H_2*nu_R,
scaled by the 11D Planck mass. After transferring this term to the
superpotential, this term gives rise to neutrino masses of the correct size at
the electroweak scale. With natural choices of the Yukawa and Kahler matrix
entries, it is possible to fit all mass, CKM and MNS experimental data. The
model predicts mu -> e + gamma decay at a rate that should be detectable for
much of the SUSY parameter space in the next round of experiments.Comment: 24 pages, 4 figures. Minor changes, references added. Some discussion
on neutrino mass generating mechanism added; no other change. Accepted for
publication in Nucl. Phys.
Anomalous U(1) symmetry and lepton flavor violation
We show that in a large class of models based on anomalous U(1) symmetry
which addresses the fermion mass hierarchy problem, leptonic flavor changing
processes are induced that are in the experimentally interesting range. The
flavor violation occurs through the renormalization group evolution of the soft
SUSY breaking parameters between the string scale and the U(1)_A breaking
scale. We derive general expressions for the evolution of these parameters in
the presence of higher dimensional operators. Several sources for the flavor
violation are identified: flavor-dependent contributions to the soft masses
from the U(1)_A gaugino, scalar mass corrections proportional to the trace of
U(1)_A charge, non-proportional A-terms from vertex corrections, and the U(1)_A
D-term. Quantitative estimates for the decays \mu -> e \gamma and \tau -> \mu
\gamma are presented in supergravity models which accommodate the relic
abundance of neutralino dark matter.Comment: References added, typos corrected, 28 pages LaTeX, includes 14 eps
figure
A new parametric equation of state and quark stars
It is still a matter of debate to understand the equation of state of cold
supra-nuclear matter in compact stars because of unknown on-perturbative strong
interaction between quarks. Nevertheless, it is speculated from an
astrophysical view point that quark clusters could form in cold quark matter
due to strong coupling at realistic baryon densities. Although it is hard to
calculate this conjectured matter from first principles, one can expect the
inter-cluster interaction to share some general features to nucleon-nucleon
interaction. We adopt a two-Gaussian component soft-core potential with these
general features and show that quark clusters can form stable simple cubic
crystal structure if we assume Gaussian form wave function. With this
parameterizing, Tolman-Oppenheimer-Volkoff equation is solved with reasonable
constrained parameter space to give mass-radius relation of crystalline solid
quark star. With baryon densities truncated at 2 times nuclear density at
surface and range of interaction fixed at 2fm we can reproduce similar
mass-radius relation to that obtained with bag model equations of state. The
maximum mass ranges from about 0.5 to 3 solar mass. Observed maximum pulsar
mass (about 2 solar mass) is then used to constrain parameters of this simple
interaction potential.Comment: 5 pages, 2 figure
Paired and clustered quantum Hall states
We briefly summarize properties of quantum Hall states with a pairing or
clustering property. Their study employs a fundamental connection with
parafermionic Conformal Field Theories. We report on closed form expressions
for the many-body wave functions and on multiplicities of the fundamental
quasi-hole excitations.Comment: 13 pages, Contribution to the proceedings of the NATO Advanced
Research Workshop "Statistical Field Theories" Como (Italy), June 18-23 200
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