84 research outputs found
Fine Tuning in Quintessence Models with Exponential Potentials
We explore regions of parameter space in a simple exponential model of the
form that are allowed by observational
constraints. We find that the level of fine tuning in these models is not
different from more sophisticated models of dark energy. We study a transient
regime where the parameter has to be less than and the
fixed point has not been reached. All values of the parameter
that lead to this transient regime are permitted. We also point out
that this model can accelerate the universe today even for , leading to a halt of the present acceleration of the universe in the
future thus avoiding the horizon problem. We conclude that this model can not
be discarded by current observations.Comment: 15 pages, 8 figure
Dipole-induced anomalous top quark couplings at the LHC
We consider direct bounds on the coefficients of higher dimensional top quark
dipole operators from their contributions to anomalous top couplings that
affect some related processes at the LHC. Several observables are studied. In
particular, we incorporate for the first time in this type of analysis the
recently measured associated production, which is currently the
only measured direct observable sensitive to the dipole operator involving the
hypercharge field. We perform a Bayesian analysis to derive the
confidence level (CL) intervals on these coefficients.Comment: 9 pages, 1 figure, 1 table; references added. Version accepted for
publication in PR
Higgs Pair Production at the LHC in Models with Universal Extra Dimensions
In this letter we study the process of gluon fusion into a pair of Higgs
bosons in a model with one universal extra dimension. We find that the
contributions from the extra top quark Kaluza-Klein excitations lead to a Higgs
pair production cross section at the LHC that can be significantly altered
compared to the Standard Model value for small values of the compactification
scale.Comment: 10 pages, 6 figures. LHC cross section computed, 2 new figure
Double Higgs Production at the LHC as a robust test of Little Higgs models
We analyze double Higgs boson production at the LHC in the context of Little
Higgs models. In double Higgs production, the diagrams involved are directly
related to those that cause the cancellation of the quadratic divergence of the
Higgs self-energy, so this mode provides a robust prediction for this class of
models. We find that in extensions of this model with the inclusion of a
so-called T-parity, there is a significant enhancement in the cross sections as
compared to the Standard Model.Comment: Presented at XXV Physics in Collision 2005, Prague, Czech Republic,
6-9 July 2005. 5 pages, 3 figure
Double Higgs Production and Quadratic Divergence Cancellation in Little Higgs Models with T Parity
We analyze double Higgs boson production at the Large Hadron Collider in the
context of Little Higgs models. In double Higgs production, the diagrams
involved are directly related to those that cause the cancellation of the
quadratic divergence of the Higgs self-energy, providing a robust prediction
for this class of models. We find that in extensions of this model with the
inclusion of a so-called T-parity, there is a significant enhancement in the
cross sections as compared to the Standard Model.Comment: 10 pages, 6 figures. v2: New references and comments on triple Higgs
coupling and signal significance adde
The Dynamical Composite Higgs
We present a simple microscopic realization of a pseudo-Nambu-Goldstone
(pNGB) boson Higgs scenario arising from the breaking of . The Higgs constituents are explicitly identified as well as the
interactions responsible for forming the bound state and breaking the
electroweak symmetry. This outcome follows from the presence of four-fermion
interactions with a super-critical coupling, and uses the Nambu-Jona-Lasinio
mechanism to break the global symmetry. The Higgs potential is found to
be insensitive to high energy scales due to the existence of an approximate
infrared fixed point. The appearance of vector resonances is described and the
correspondence with other proposals in the literature established. The model
described here is significantly simpler than other recent ultraviolet
completions of pNGB scenarios. The observed Higgs mass can be accommodated, and
agreement with electroweak precision tests achieved in certain regions of
parameter space. There are also new vector-like fermions, some of which may lie
within reach of the LHC. In addition, we predict a heavy standard model singlet
scalar in the multi-TeV range. The amount of fine-tuning required in the model
is studied. Finally, we show that such a scheme can be completed in the
ultraviolet by a renormalizable theory.Comment: 32 pages plus appendices, 7 figures - reference adde
WIMP and SIMP Dark Matter from the Spontaneous Breaking of a Global Group
We propose and study a scalar extension of the Standard Model which respects
a symmetry remnant of the spontaneous breaking of a global
symmetry. Consequently, this model has a natural dark matter
candidate and a Goldstone boson in the physical spectrum. In addition, the
Higgs boson properties are changed with respect to the Standard Model due to
the mixing with a new particle. We explore regions in the parameter space
taking into account bounds from the measured Higgs properties, dark matter
direct detection as well as measurements of the effective number of neutrino
species before recombination. The dark matter relic density is determined by
three classes of processes: the usual self-annihilation, semi-annihilation and
purely dark matter processes. The latter has been subject of recent
interest leading to the so-called `Strongly Interacting Massive Particle'
(SIMP) scenario. We show under which conditions our model can lead to a
concrete realization of such scenario and study the possibility that the dark
matter self-interactions could address the small scale structure problems. In
particular, we find that in order for the SIMP scenario to work, the dark
matter mass must be in the range MeV, with the global symmetry energy
breaking scale in the TeV range.Comment: 28 pages, 17 artistic figures. Accepted for publication in JCA
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