6,902 research outputs found
Cosmological Constants as Messenger between Branes
We present a supersymmetry-breaking scenario in which both the breaking in
the hidden sector with no-scale type supergravity and that in the observable
sector with gauge mediation are taken into account. The breaking scales in the
hidden and observable sectors are related through the vanishing condition of
the cosmological constant with a brane-world picture in mind. Suppressing
flavor-changing neutral currents, we can naturally obtain the gravitino,
Higgs(ino), and soft masses of the electroweak scale.Comment: 7 pages, Late
When is Multimetric Gravity Ghost-free?
We study ghosts in multimetric gravity by combining the mini-superspace and
the Hamiltonian constraint analysis. We first revisit bimetric gravity and
explain why it is ghost-free. Then, we apply our method to trimetric gravity
and clarify when the model contains a ghost. More precisely, we prove trimetric
gravity generically contains a ghost. However, if we cut the interaction of a
pair of metrics, trimetric gravity becomes ghost-free. We further extend the
Hamiltonian analysis to general multimetric gravity and calculate the number of
ghosts in various models. Thus, we find multimetric gravity with loop type
interactions never becomes ghost-free.Comment: 22 pages, 6 figure
Inflationary paradigm after Planck 2013
Models of cosmic inflation posit an early phase of accelerated expansion of
the universe, driven by the dynamics of one or more scalar fields in curved
spacetime. Though detailed assumptions about fields and couplings vary across
models, inflation makes specific, quantitative predictions for several
observable quantities, such as the flatness parameter ()
and the spectral tilt of primordial curvature perturbations (), among others---predictions that match the latest
observations from the {\it Planck} satellite to very good precision. In the
light of data from {\it Planck} as well as recent theoretical developments in
the study of eternal inflation and the multiverse, we address recent criticisms
of inflation by Ijjas, Steinhardt, and Loeb. We argue that their conclusions
rest on several problematic assumptions, and we conclude that cosmic inflation
is on a stronger footing than ever before.Comment: 11 pages, no figures; added references, and brief additions to
Footnote 1, Section VI, and the Acknowledgment
Simple Scheme for Gauge Mediation
We present a simple scheme for constructing models that achieve successful
gauge mediation of supersymmetry breaking. In addition to our previous work [1]
that proposed drastically simplified models using metastable vacua of
supersymmetry breaking in vector-like theories, we show there are many other
successful models using various types of supersymmetry breaking mechanisms that
rely on enhanced low-energy U(1)_R symmetries. In models where supersymmetry is
broken by elementary singlets, one needs to assume U(1)_R violating effects are
accidentally small, while in models where composite fields break supersymmetry,
emergence of approximate low-energy U(1)_R symmetries can be understood simply
on dimensional grounds. Even though the scheme still requires somewhat small
parameters to sufficiently suppress gravity mediation, we discuss their
possible origins due to dimensional transmutation. The scheme accommodates a
wide range of the gravitino mass to avoid cosmological problems.Comment: 13 page
Dependence of the intrinsic spin Hall effect on spin-orbit interaction character
We report on a comparative numerical study of the spin Hall conductivity in
two-dimensions for three different spin-orbit interaction models; the standard
k-linear Rashba model, the k-cubic Rashba model that describes two-dimensional
hole systems, and a modified k-linear Rashba model in which the spin-orbit
coupling strength is energy dependent. Numerical finite-size Kubo formula
results indicate that the spin Hall conductivity of the k-linear Rashba model
vanishes for frequency much smaller than the scattering rate
, with order one relative fluctuations surviving out to large system
sizes. For the k-cubic Rashba model case, the spin Hall conductivity does not
depend noticeably on and is finite in the {\em dc} limit, in
agreement with experiment. For the modified k-linear Rashba model the spin Hall
conductivity is noticeably dependent but approaches a finite
value in the {\em dc} limit. We discuss these results in the light of a
spectral decomposition of the spin Hall conductivity and associated sum rules,
and in relation to a proposed separation of the spin Hall conductivity into
skew-scattering, intrinsic, and interband vertex correction contributions.Comment: 10 pages, 4 figure
Softly Broken Supersymmetric Desert from Orbifold Compactification
A new viewpoint for the gauge hierarchy problem is proposed: compactification
at a large scale, 1/R, leads to a low energy effective theory with
supersymmetry softly broken at a much lower scale, \alpha/R. The hierarchy is
induced by an extremely small angle \alpha which appears in the orbifold
compactification boundary conditions. The same orbifold boundary conditions
break Peccei-Quinn symmetry, leading to a new solution to the \mu problem.
Explicit 5d theories are constructed with gauge groups SU(3) \times SU(2)
\times U(1) and SU(5), with matter in the bulk or on the brane, which lead to
the (next-to) minimal supersymmetric standard model below the compactification
scale. In all cases the soft supersymmetry-breaking and \mu parameters
originate from bulk kinetic energy terms, and are highly constrained. The
supersymmetric flavor and CP problems are solved.Comment: 18 pages, Latex, corrected values for A parameter
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