2,795 research outputs found
Classical and Quantum Brane Cosmology
The first part of this lecture quickly touches upon some important but
infrequently discussed issues in large extra dimension and warped extra
dimension scenarios, with particular reference to effects in the early
universe. The second part discusses a modification and extension of an earlier
proposal by Brown and Teitelboim to relax the effective cosmological term by
nucleation of fundamental membranes.Comment: 12 pages, latex using aipproc2.st
Axion-Assisted Electroweak Baryogenesis
We consider a hidden-valley gauge sector, G, with strong coupling scale
Lambda~TeV and CP-violating topological parameter, theta, as well as a new
axion degree of freedom which adjusts theta to near zero in the current
universe. If the G-sector couples to the Standard Model via weak-scale states
charged under both, then in the early universe it is possible for the
CP-violation due to theta (which has not yet been adjusted to zero by the
hidden axion) to feed in to the SM and drive efficient baryogenesis during the
electroweak (EW) phase transition, independent of the effectively small amount
of CP violation present in the SM itself. While current constraints on both the
new axion and charged states are easily satisfied, we argue that the LHC can
investigate the vast majority of parameter space where EW-baryogenesis is
efficiently assisted, while the hidden axion should comprise a significant
fraction of the dark matter density. In the supersymmetric version, the
``messenger'' matter communicating between the SM- and G-sectors naturally
solves the little hierarchy problem of the MSSM. The connection of the hidden
scale and masses of the ``quirk''-like messengers to the EW scale via the
assisted electroweak baryogenesis mechanism provides a reason for such new
hidden valley physics to lie at the weak scale.Comment: 22+1 pages, 3 figure
A Survey of Residual Cancer Risks Permitted by Health, Safety and Environmental Policy
The authors describe permitted U.S. residual cancer risks, focusing on numerical levels specifically and implicitly authorized by statute or regulation. They also discuss potential changes
Baryogenesis via Particle-Antiparticle Oscillations
CP violation, which is crucial for producing the baryon asymmetry of the
Universe, is enhanced in particle-antiparticle oscillations. We study
particle-antiparticle oscillations (of a particle with mass O(100 GeV)) with CP
violation in the early Universe in the presence of interactions with O(ab-fb)
cross-sections. We show that, if baryon-number-violating interactions exist, a
baryon asymmetry can be produced via out-of-equilibrium decays of oscillating
particles. As a concrete example we study a -symmetric,
R-parity-violating SUSY model with pseudo-Dirac gauginos, which undergo
particle-antiparticle oscillations. Taking bino to be the lightest
-symmetric particle, and assuming it decays via baryon-number-violating
interactions, we show that bino-antibino oscillations can produce the baryon
asymmetry of the Universe.Comment: 17 pages, 11 figures, refs added, typos fixe
Retrofitted Natural Supersymmetry from a U(1)
We propose that a single, spontaneously broken, U(1) gauge symmetry may be
responsible for suppressing both the first two generation Yukawa couplings, and
also, in a correlated manner, parameters in the dynamical supersymmetry (SUSY)
breaking sector by the mechanism of retrofitting. In the dynamical SUSY
breaking sector, these small parameters are typically required in order to
introduce R-symmetry breaking in a controlled manner and obtain
phenomenologically viable meta-stable vacua. The heavy U(1) multiplet mediates
a dominant contribution to the first two generation MSSM sfermion soft masses,
while gauge mediation provides a parametrically suppressed soft term
contribution to the stop and most other states, so realising a natural SUSY
spectrum in a fashion consistent with SUSY unification. In explicit models the
spectra obtained can be such that current LHC limits are evaded, and
predictions of flavour changing processes are consistent with observation. We
examine both implementations with low scale mediation, and string-motivated
examples where the U(1) is anomalous before the inclusion of a generalised
Green-Schwarz mechanism.Comment: V2: References adde
Rare Flavor Processes in Maximally Natural Supersymmetry
We study CP-conserving rare flavor violating processes in the recently
proposed theory of Maximally Natural Supersymmetry (MNSUSY). MNSUSY is an
unusual supersymmetric (SUSY) extension of the Standard Model (SM) which,
remarkably, is un-tuned at present LHC limits. It employs Scherk-Schwarz
breaking of SUSY by boundary conditions upon compactifying an underlying
5-dimensional (5D) theory down to 4D, and is not well-described by
softly-broken SUSY, with much different phenomenology than the
Minimal Supersymmetric Standard Model (MSSM) and its variants. The usual
CP-conserving SUSY-flavor problem is automatically solved in MNSUSY due to a
residual almost exact symmetry, naturally heavy and highly degenerate
1st- and 2nd-generation sfermions, and heavy gauginos and Higgsinos. Depending
on the exact implementation of MNSUSY there exist important new sources of
flavor violation involving gauge boson Kaluza-Klein (KK) excitations. The
spatial localization properties of the matter multiplets, in particular the
brane localization of the 3rd generation states, imply KK-parity is broken and
{\it tree-level} contributions to flavor changing neutral currents are present
in general. Nevertheless, we show that simple variants of the basic MNSUSY
model are safe from present flavor constraints arising from kaon and -meson
oscillations, the rare decays ,
and - conversion in nuclei. We also briefly discuss some special
features of the radiative decays and . Future experiments, especially those concerned with lepton flavor
violation, should see deviations from SM predictions unless one of the MNSUSY
variants with enhanced flavor symmetries is realized.Comment: 28 pages, 19 figures; references added, typos correcte
Pseudo-Goldstones from Supersymmetric Wilson Lines on 5D Orbifolds
We consider a U(1) gauge theory on the five dimensional orbifold
, where has even parity. This leads to
a light pseudoscalar degree of freedom in the effective 4D theory below
the compactification scale arising from a gauge-invariant brane-to-brane Wilson
line. As noted by Arkani-Hamed et al in the non-supersymmetric case the
5D bulk gauge-invariance of the underlying theory together with the non-local
nature of the Wilson line field leads to the protection of the 4D theory of
from possible large global-symmetry violating quantum gravitational
effects. We study the theory in detail, in particular developing the
supersymmetric generalization of this construction, involving a pseudoscalar
Goldstone field (the `axion') and its scalar and fermion superpartners
(`saxion' and `axino'). The global nature of implies the absence of
independent Kaluza-Klein excitations of its component fields. The
non-derivative interactions of the (supersymmetric) Wilson line in the
effective 4D theory arising from U(1) charged 5D fields propagating
between the boundary branes are studied. We show that, similar to the
non-supersymmetric case, these interactions are suppressed by where is the size of the extra dimension.Comment: LaTex, 16 page
Inducing the mu and the B mu Term by the Radion and the 5d Chern-Simons Term
In 5-dimensional models with gauge-Higgs unification, the F-term vacuum
expectation value of the radion provides, in close analogy to the
Giudice-Masiero mechanism, a natural source for the mu and B mu term. Both the
leading order gauge theory lagrangian and the supersymmetric Chern-Simons term
contain couplings to the radion superfield which can be used for this purpose.
We analyse the basic features of this mechanism for mu term generation and
provide an explicit example, based on a variation of the SU(6) gauge-Higgs
unification model of Burdman and Nomura. This construction contains all the
relevant features used in our generic analysis. More generally, we expect our
mechanism to be relevant to many of the recently discussed orbifold GUT models
derived from heterotic string theory. This provides an interesting way of
testing high-scale physics via Higgs mass patterns accessible at the LHC.Comment: 23 pages, LaTeX, 1 figure, concrete model significantly improved,
references adde
Axion Mediation
We explore the possibility that supersymmetry breaking is mediated to the
Standard Model sector through the interactions of a generalized axion multiplet
that gains a F-term expectation value. Using an effective field theory
framework we enumerate the most general possible set of axion couplings and
compute the Standard Model sector soft-supersymmetry-breaking terms. Unusual,
non-minimal spectra, such as those of both natural and split supersymmetry are
easily implemented. We discuss example models and low-energy spectra, as well
as implications of the particularly minimal case of mediation via the QCD axion
multiplet. We argue that if the Peccei-Quinn solution to the strong-CP problem
is realized in string theory then such axion-mediation is generic, while in a
field theory model it is a natural possibility in both DFSZ- and KSVZ-like
regimes. Axion mediation can parametrically dominate gravity-mediation and is
also cosmologically beneficial as the constraints arising from axino and
gravitino overproduction are reduced. Finally, in the string context, axion
mediation provides a motivated mechanism where the UV completion naturally
ameliorates the supersymmetric flavor problem.Comment: 32 pages, 3 figures, references added, minor change
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