106 research outputs found
Neutrino masses in the Lepton Number Violating MSSM
We consider the most general supersymmetric model with minimal particle
content and an additional discrete Z_3 symmetry (instead of R-parity), which
allows lepton number violating terms and results in non-zero Majorana neutrino
masses. We investigate whether the currently measured values for lepton masses
and mixing can be reproduced. We set up a framework in which Lagrangian
parameters can be initialised without recourse to assumptions concerning
trilinear or bilinear superpotential terms, CP-conservation or
intergenerational mixing and analyse in detail the one loop corrections to the
neutrino masses. We present scenarios in which the experimental data are
reproduced and show the effect varying lepton number violating couplings has on
the predicted atmospheric and solar mass^2 differences. We find that with
bilinear lepton number violating couplings in the superpotential of the order 1
MeV the atmospheric mass scale can be reproduced. Certain trilinear
superpotential couplings, usually, of the order of the electron Yukawa coupling
can give rise to either atmospheric or solar mass scales and bilinear
supersymmetry breaking terms of the order 0.1 GeV^2 can set the solar mass
scale. Further details of our calculation, Lagrangian, Feynman rules and
relevant generic loop diagrams, are presented in three Appendices.Comment: 48 pages, 7 figures, v2 references added, typos corrected, published
versio
Quantum Hall effect anomaly and collective modes in the magnetic-field-induced spin-density-wave phases of quasi-one-dimensional conductors
We study the collective modes in the magnetic-field-induced spin-density-wave
(FISDW) phases experimentally observed in organic conductors of the Bechgaard
salts family. In phases that exhibit a sign reversal of the quantum Hall effect
(Ribault anomaly), the coexistence of two spin-density waves gives rise to
additional collective modes besides the Goldstone modes due to spontaneous
translation and rotation symmetry breaking. These modes strongly affect the
charge and spin response functions. We discuss some experimental consequences
for the Bechgaard salts.Comment: Final version (LaTex, 8 pages, no figure), to be published in
Europhys. Let
Critical Exponents of the Three Dimensional Random Field Ising Model
The phase transition of the three--dimensional random field Ising model with
a discrete () field distribution is investigated by extensive Monte
Carlo simulations. Values of the critical exponents for the correlation length,
specific heat, susceptibility, disconnected susceptibility and magnetization
are determined simultaneously via finite size scaling. While the exponents for
the magnetization and disconnected susceptibility are consistent with a first
order transition, the specific heat appears to saturate indicating no latent
heat. Sample to sample fluctuations of the susceptibilty are consistent with
the droplet picture for the transition.Comment: Revtex, 10 pages + 4 figures included as Latex files and 1 in
Postscrip
A Study of Activated Processes in Soft Sphere Glass
On the basis of long simulations of a binary mixture of soft spheres just
below the glass transition, we make an exploratory study of the activated
processes that contribute to the dynamics. We concentrate on statistical
measures of the size of the activated processes.Comment: 17 pages, 9 postscript figures with epsf, uses harvmac.te
Conformal Enhancement of Holographic Scaling in Black Hole Thermodynamics: A Near-Horizon Heat-Kernel Framework
Standard thermodynamic treatments of quantum field theory in the presence of
black-hole backgrounds reproduce the black hole entropy by usually specializing
to the leading order of the heat-kernel or the high-temperature expansion. By
contrast, this work develops a hybrid framework centered on geometric spectral
asymptotics whereby these assumptions are shown to be unwarranted insofar as
black hole thermodynamics is concerned. The approach--consisting of the
concurrent use of near-horizon and heat-kernel asymptotic expansions--leads to
a proof of the holographic scaling of the entropy as a universal feature driven
by conformal quantum mechanics.Comment: 13 pages, JHEP style. Added section 3 in the new version and a few
typos were correcte
Open String Wavefunctions in Warped Compactifications
We analyze the wavefunctions for open strings in warped compactifications,
and compute the warped Kahler potential for the light modes of a probe D-brane.
This analysis not only applies to the dynamics of D-branes in warped
backgrounds, but also allows to deduce warping corrections to the closed string
Kahler metrics via their couplings to open strings. We consider in particular
the spectrum of D7-branes in warped Calabi-Yau orientifolds, which provide a
string theory realizations of the Randall-Sundrum scenario. We find that
certain background fluxes, necessary in the presence of warping, couple to the
fermionic wavefunctions and qualitatively change their behavior. This modified
dependence of the wavefunctions are needed for consistency with supersymmetry,
though it is present in non-supersymmetric vacua as well. We discuss the
deviations of our setup from the RS scenario and, as an application of our
results, compute the warping corrections to Yukawa couplings in a simple model.
Our analysis is performed both with and without the presence of D-brane
world-volume flux, as well as for the case of backgrounds with varying dilaton.Comment: 52 pages, refs. added, minor correction
The Little Hierarchy in Universal Extra Dimensions
In the standard model in universal extra dimensions (UED) the mass of the
Higgs field is driven to the cutoff of the higher-dimensional theory. This
re-introduces a small hierarchy since the compactification scale 1/R should not
be smaller than the weak scale. In this paper we study possible solutions to
this problem by considering five-dimensional theories where the Higgs field
potential vanishes at tree level due to a global symmetry. We consider two
avenues: a Little Higgs model and a Twin Higgs model. An obstacle for the
embedding of these four-dimensional models in five dimensions is that their
logarithmic sensitivity to the cutoff will result in linear divergences in the
higher dimensional theory. We show that, despite the increased cutoff
sensitivity of higher dimensional theories, it is possible to control the Higgs
mass in these two scenarios. For the Little Higgs model studied, the
phenomenology will be significantly different from the case of the standard
model in UED. This is due to the fact that the compactification scale
approximately coincides with the scale where the masses of the new states
appear. For the case of the Twin Higgs model, the compactification scale may be
considerably lower than the scale where the new states appear. If it is as low
as allowed by current limits, it would be possible to experimentally observe
the standard model Kaluza-Klein states as well as a new heavy quark. On the
other hand, if the compactification scale is higher, then the phenomenology at
colliders would coincide with the one for the standard model in UED.Comment: 25 pages, 2 figure
Boundary States of c=1 and 3/2 Rational Conformal Field Theories
We study the boundary states for the rational points in the moduli spaces of
c=1 conformal and c=3/2 superconformal field theories, including the isolated
Ginsparg points. We use the orbifold and simple-current techniques to relate
the boundary states of different theories and to obtain symmetry-breaking,
non-Cardy boundary states. We show some interesting examples of fractional and
twisted branes on orbifold spaces.Comment: Latex, 46 pages, 1 figur
Mixed Wino Dark Matter: Consequences for Direct, Indirect and Collider Detection
In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass
unification, the predicted relic abundance of neutralinos usually exceeds the
strict limits imposed by the WMAP collaboration. One way to obtain the correct
relic abundance is to abandon gaugino mass universality and allow a mixed
wino-bino lightest SUSY particle (LSP). The enhanced annihilation and
scattering cross sections of mixed wino dark matter (MWDM) compared to bino
dark matter lead to enhanced rates for direct dark matter detection, as well as
for indirect detection at neutrino telescopes and for detection of dark matter
annihilation products in the galactic halo. For collider experiments, MWDM
leads to a reduced but significant mass gap between the lightest neutralinos so
that chi_2^0 two-body decay modes are usually closed. This means that dilepton
mass edges-- the starting point for cascade decay reconstruction at the CERN
LHC-- should be accessible over almost all of parameter space. Measurement of
the m_{\tz_2}-m_{\tz_1} mass gap at LHC plus various sparticle masses and cross
sections as a function of beam polarization at the International Linear
Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in
the universe.Comment: 29 pages including 19 eps figure
Gauge thresholds in the presence of oblique magnetic fluxes
We compute the one-loop partition function and analyze the conditions for
tadpole cancellation in type I theories compactified on tori in the presence of
internal oblique magnetic fields. We check open - closed string channel duality
and discuss the effect of T-duality. We address the issue of the quantum
consistency of the toroidal model with stabilized moduli recently proposed by
Antoniadis and Maillard (AM). We then pass to describe the computation of
one-loop threshold corrections to the gauge couplings in models of this kind.
Finally we briefly comment on coupling unification and dilaton stabilization in
phenomenologically more viable modelsComment: 34 pages, 2 figures; references added, major changes to the
discussion of the model proposed by Antoniadis and Maillar
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