12,748 research outputs found
Neutrino Oscillation and Charged Lepton-Flavor Violation in the Supersymmetric Standard Models
The neutrino experiment results suggest that the neutrinos have finite masses
and the lepton-flavor symmetries are violating in nature. In the supersymmetric
models, the charged lepton-flavor violating processes, such as mu -> e gamma
and tau -> mu gamma, may have the branching ratios accessible to the future
experiments, depending on origins of the neutrino masses and the SUSY breaking.
In this paper we discuss the branching ratios in the supergravity scenario
using the current solar and atmospheric neutrino experimental data.Comment: 12 pages. Talk given at the Workshop on High Intensity Muon Sources
(HIMUS99), Tsukuba, Japan, 1-4 Dec 199
Molecular Hydrogen Emission from Protoplanetary Disks
We have modeled self-consistently the density and temperature profiles of gas
and dust in protoplanetary disks, taking into account irradiation from a
central star. Making use of this physical structure, we have calculated the
level populations of molecular hydrogen and the line emission from the disks.
As a result, we can reproduce the observed strong line spectra of molecular
hydrogen from protoplanetary disks, both in the ultraviolet (UV) and the
near-infrared, but only if the central star has a strong UV excess radiation.Comment: 19 pages, accepted for publication in Astronomy and Astrophysic
Unification of Weak and Hypercharge Interactions at the TeV Scale
A realistic SU(3)_C x SU(3)_W unified theory is constructed with a TeV sized
extra dimension compactified on the orbifold S_1/Z_2, leaving only the standard
model gauge group SU(3)_C x SU(2)_L x U(1)_Y unbroken in the low energy 4D
theory. The Higgs doublets are zero modes of bulk SU(3)_W triplets and serve to
normalize the hypercharge generator, apparently giving a tree-level prediction
for the weak mixing angle: \sin^2\theta = 1/4. The orbifold boundary conditions
imply a restricted set of SU(3)_W gauge transformations: at an orbifold fixed
point only the transformations of SU(2)_L x U(1)_Y are operative. This allows
quarks to be located at this fixed point, overcoming the longstanding problem
of how to incorporate matter in a unified SU(3)_W theory. However, in general
this local, explicit breaking of SU(3)_W symmetry, necessary for including
quarks into the theory, destroys the tree-level prediction for the weak mixing
angle. This apparent contradiction is reconciled by making the volume of the
extra dimension large, diluting the effects of the local SU(3)_W violation. In
the case that the electroweak theory is strongly coupled at the cutoff scale of
the effective theory, radiative corrections to the weak mixing angle can be
reliably computed, and used to predict the scale of compactification: 1 - 2 TeV
without supersymmetry, and in the region of 3 - 6 TeV for a supersymmetric
theory. The experimental signature of electroweak unification into SU(3)_W is a
set of ``weak partners'' of mass 1/2R, which are all electrically charged and
are expected to be accessible at LHC. These include weak doublets of gauge
particles of electric charge (++,+), and a charged scalar. When pair produced,
they yield events containing multiple charged leptons, missing large transverse
energy and possibly Higgs and electroweak gauge bosons.Comment: 13 pages, LaTeX, note added on charge quantizatio
Grand Unification and Intermediate Scale Supersymmetry
With minimal field content and for an interesting range of the supersymmetric
Higgs mixing parameter, 0.5 < tan^2 \beta < 2, the superpartner mass scale,
\tilde{m}, is found to be at the intermediate scale, ~ 10^{10 \pm 1} GeV, near
where the Standard Model Higgs quartic coupling passes through zero. For any 4d
supersymmetric grand unified symmetry spontaneously broken by a vacuum
expectation value , if superpotential interactions for \Sigma are
forbidden e.g. by R symmetries, the uneaten color octet, \Sigma_8, and weak
triplet, \Sigma_3, have masses of order \tilde{m}. The combination of
superpartner and \Sigma_{8,3} states leads to successful gauge coupling
unification, removing the disastrously high proton decay rate of minimal
Standard Model unification. Proton decay could be seen in future experiments if
\tilde{m} ~ 10^{11} GeV, but not if it is lower. If the reheating temperature
after inflation, T_R, is less than \tilde{m} dark matter may be axions. If T_R
> \tilde{m}, thermal LSP dark matter may lead to the environmental selection of
a TeV-scale LSP, either wino or Higgsino, which could comprise all or just one
component of dark matter. In the Higgsino case, the dark matter is found to
behave inelastically in direct detection experiments, and gauge coupling
unification occurs accurately without the need of any threshold corrections.Comment: 14 pages, 3 figures; version to appear in JHE
The Entropy of a Vacuum: What Does the Covariant Entropy Count?
We argue that a unitary description of the formation and evaporation of a
black hole implies that the Bekenstein-Hawking entropy is the "entropy of a
vacuum": the logarithm of the number of possible independent ways in which
quantum field theory on a fixed classical spacetime background can emerge in a
full quantum theory of gravity. In many cases, the covariant entropy counts
this entropy--the degeneracy of emergent quantum field theories in full quantum
gravity--with the entropy of particle excitations in each quantum field theory
giving only a tiny perturbation. In the Rindler description of a (black hole)
horizon, the relevant vacuum degrees of freedom manifest themselves as an extra
hidden quantum number carried by the states representing the second exterior
region; this quantum number is invisible in the emergent quantum field theory.
In a distant picture, these states arise as exponentially degenerate ground and
excited states of the intrinsically quantum gravitational degrees of freedom on
the stretched horizon. The formation and evaporation of a black hole involve
processes in which the entropy of collapsing matter is transformed into that of
a vacuum and then to that of final-state Hawking radiation. In the intermediate
stage of this evolution, entanglement between the vacuum and (early) Hawking
radiation develops, which is transferred to the entanglement among final-state
Hawking quanta through the evaporation process. The horizon is kept smooth
throughout the evolution; in particular, no firewall develops. Similar
considerations also apply for cosmological horizons, for example for the
horizon of a meta-stable de-Sitter space.Comment: 30 pages; v2: references added, minor revisions; v3: footnotes 2 and
7 added for the journal versio
Berezinskii-Kosterlitz-Thouless transitions in the six-state clock model
Classical 2D clock model is known to have a critical phase with
Berezinskii-Kosterlitz-Thouless(BKT) transitions. These transitions have
logarithmic corrections which make numerical analysis difficult. In order to
resolve this difficulty, one of the authors has proposed the method called
level spectroscopy, which is based on the conformal field theory. We extend
this method to the multi-degenerated case. As an example, we study the
classical 2D 6-clock model which can be mapped to the quantum self-dual 1D
6-clock model. Additionally, we confirm that the self-dual point has a precise
numerical agreement with the analytical result, and we argue the degeneracy of
the excitation states at the self-dual point from the effective field
theoretical point of view.Comment: 18pages, 7figure
Dimension-six Proton Decays in the Modified Missing Doublet SU(5) Model
Dimension-five operators for nucleon decays are suppressed in the modified
missing doublet (MMD) model in the supersymmetric SU(5) grand unification. We
show that nonrenormalizable interactions decrease the unification scale in the
MMD model which increases the nucleon decay rate of dimension-six operators by
a significant amount. We find that the theoretical lower bound on the proton
life time \tau(p \to \e^+ \pi^0) is within the observable range at
SuperKamiokande.Comment: 9 pages, Latex, 1 Postscript figure
Grand Unification, Axion, and Inflation in Intermediate Scale Supersymmetry
A class of supersymmetric grand unified theories is introduced that has a
single scale below the cutoff, that of the supersymmetry breaking masses
. For a wide range of the dimensionless parameters, agreement with
the observed mass of the Higgs boson determines , yielding Intermediate Scale Supersymmetry. We show that within this
framework it is possible for seesaw neutrino masses, axions, and inflation to
be described by the scale , offering the possibility of a unified
origin of disparate phenomena. Neutrino masses allowing for thermal
leptogenesis can be obtained, and the axion decay constant lies naturally in
the range , consistent with a recent
observational suggestion of high scale inflation. A minimal model is
presented that illustrates these features. In this model, the only states at
the grand unified scale are those of the heavy gauge supermultiplet. The grand
unified partners of the Higgs doublets have a mass of order ,
leading to the dominant proton decay mode , which
may be probed in upcoming experiments. Dark matter may be winos, with mass
environmentally selected to the TeV scale, and/or axions. Gauge coupling
unification is found to be successful, especially if the wino is at the TeV
scale.Comment: 27 pages, 7 figures; minor corrections, references and discussion
adde
Low Energy Description of Quantum Gravity and Complementarity
We consider a framework in which low energy dynamics of quantum gravity is
described preserving locality, and yet taking into account the effects that are
not captured by the naive global spacetime picture, e.g. those associated with
black hole complementarity. Our framework employs a "special relativistic"
description of gravity; specifically, gravity is treated as a force measured by
the observer tied to the coordinate system associated with a freely falling
local Lorentz frame. We identify, in simple cases, regions of spacetime in
which low energy local descriptions are applicable as viewed from the freely
falling frame; in particular, we identify a surface called the gravitational
observer horizon on which the local proper acceleration measured in the
observer's coordinates becomes the cutoff (string) scale. This allows for
separating between the "low-energy" local physics and "trans-Planckian"
intrinsically quantum gravitational (stringy) physics, and allows for
developing physical pictures of the origins of various effects. We explore the
structure of the Hilbert space in which the proposed scheme is realized in a
simple manner, and classify its elements according to certain horizons they
possess. We also discuss implications of our framework on the firewall problem.
We conjecture that the complementarity picture may persist due to properties of
trans-Planckian physics.Comment: 18 pages, 1 figure; matches published versio
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