4,920 research outputs found
Cosmology and Hierarchy in Stabilized Warped Brane Models
We examine the cosmology and hierarchy of scales in models with branes
immersed in a five-dimensional curved spacetime subject to radion
stabilization. When the radion field is time-independent and the inter-brane
spacing is stabilized, the universe can naturally find itself in the
radiation-dominated epoch. This feature is independent of the form of the
stabilizing potential. We recover the standard Friedmann equations without
assuming a specific form for the bulk energy-momentum tensor. In the models
considered, if the observable brane has positive tension, a solution to the
hierarchy problem requires the presence of a negative tension brane somewhere
in the bulk. We find that the string scale can be as low as the electroweak
scale. In the situation of self-tuning branes where the bulk cosmological
constant is set to zero, the brane tensions have hierarchical values. In the
case of a polynomial stabilizing potential no new hierarchy is created.Comment: Version to appear in PL
Some Phenomenology of Intersecting D-Brane Models
We present some phenomenology of a new class of intersecting D-brane models.
Soft SUSY breaking terms for these models are calculated in the u - moduli
dominant SUSY breaking approach (in type IIA). In this case, the dependence of
the soft terms on the Yukawas and Wilson lines drops out. These soft terms have
a different pattern compared to the usual heterotic string models.
Phenomenological implications for dark matter are discussed.Comment: 29 pages, 1 figure, References adde
String Fields and the Standard Model
The Cremmer-Scherk mechanism is generalised in a non-Abelian context. In the
presence of the Higgs scalars of the standard model it is argued that fields
arising from the low energy effective string action may contribute to the mass
generation of the observed vector bosons that mediate the electroweak
interactions and that future analyses of experimental data should consider the
possibility of string induced radiative corrections to the Weinberg angle
coming from physics beyond the standard model.Comment: 4 pages, LATEX, no figure
Thermodynamic properties of spontaneous magnetization in Chern-Simons QED_3
The spontaneous magnetization in Chern-Simons QED_3 is discussed in a finite
temperature system. The thermodynamical potential is analyzed within the weak
field approximation and in the fermion massless limit. We find that there is a
linear term with respect to the magnetic field with a negative coefficient at
any finite temperature. This implies that the spontaneous magnetic field does
not vanish even at high temperature. In addition, we examine the photon
spectrum in the system. We find that the bare Chern-Simons coefficient is
cancelled by the radiative effects. The photons then become topologically
massless according to the magnetization, though they are massive by finite
temperature effects. Thus the magnetic field is a long-range force without the
screening even at high temperature.Comment: 32 pages, Latex, 4 eps figure
Self-accelerating solutions of scalar-tensor gravity
Scalar-tensor gravity is the simplest and best understood modification of
general relativity, consisting of a real scalar field coupled directly to the
Ricci scalar curvature. Models of this type have self-accelerating solutions.
In an example inspired by string dilaton couplings, scalar-tensor gravity
coupled to ordinary matter exhibits a de Sitter type expansion, even in the
presence of a {\it negative} cosmological constant whose magnitude exceeds that
of the matter density. This unusual behavior does not require phantoms, ghosts
or other exotic sources. More generally, we show that any expansion history can
be interpreted as arising partly or entirely from scalar-tensor gravity. To
distinguish any quintessence or inflation model from its scalar-tensor
variants, we use the fact that scalar-tensor models imply deviations of the
post-Newtonian parameters of general relativity, and time variation of the
Newton's gravitational coupling . We emphasize that next-generation probes
of modified GR and the time variation of are an essential complement to
dark energy probes based on luminosity-distance measurements.Comment: 14 pages, 3 figure
Summary of the Very Large Hadron Collider Physics and Detector Workshop
One of the options for an accelerator beyond the LHC is a hadron collider
with higher energy. Work is going on to explore accelerator technologies that
would make such a machine feasible. This workshop concentrated on the physics
and detector issues associated with a hadron collider with an energy in the
center of mass of the order of 100 to 200 TeV
Semileptonic decays of the standard Higgs boson
The Higgs boson decay into a pair of real or virtual W bosons, with one of
them decaying leptonically, is predicted within the Standard Model to have the
largest branching fraction of all Higgs decays that involve an isolated
electron or muon, for M_h > 120 GeV. We compute analytically the
fully-differential width for this h -> l \nu jj decay at tree level, and then
explore some multi-dimensional cuts that preserve the region of large signal.
Future searches for semileptonic decays at the Tevatron and LHC, employing
fully-differential information as outlined here, may be essential for ruling
out or in the Higgs boson and for characterizing a Higgs signal.Comment: 17 pages, 5 .eps figure
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