535 research outputs found
Dark matter clues in the muon anomalous magnetic moment
We study the possibility to explain the non-baryonic dark matter abundance
and improve the present fits on the muon anomalous magnetic moment through the
same new physics. The only viable way to solve simultaneously both problems
which is known to date is by using supersymmetric theories. However in this
work we show that massive brane fluctuations (branons) in large
extra-dimensions models can provide a more economical alternative to
supersymmetry. This is so because the low-energy branon physics depends
effectively on only three parameters. Next collider experiments, such as LHC or
ILC, will be sensitive to branon phenomenology in the natural parameter region
where the theory is able to account for the two effects.Comment: 4 pages, 3 figures, REVTeX
Some consequences of the effective low-energy lagrangian for gravity
We consider the minimal low-energy action for gravity up to six derivatives
which is renormalizable at the two-loop level modulo higher derivative
corrections. Then we study the classical solutions corresponding to the
Schwarzschild and the Robertson-Walker metrics. In the first case we find a
singularity close to the gravitational radius and in the second case we find
inflationary de Sitter solutions in absence of any matter or cosmological
constant.Comment: 13 page
Black holes in modified gravity theories
In the context of gravity theories, the issue of finding static and
spherically symmetric black hole solutions is addressed. Two approaches to
study the existence of such solutions are considered: first, constant curvature
solutions, and second, the general case (without imposing constant curvature)
is also studied. Performing a perturbative expansion around the
Einstein-Hilbert action, it is found that only solutions of the
Schwarzschild-(Anti-) de Sitter type are present (up to second order in
perturbations) and the explicit expressions for these solutions are provided in
terms of the function. Finally we consider the thermodynamics of black
holes in Anti-de Sitter space-time and study their local and global stability.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish
Relativity Meeting 2009, Bilbao, Spain, 7-11 September 200
Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation
In this note we provide a simple explanation of the recent finding of
anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston
(astro-ph/9704196). We consider, as a possible origin of such effect, the
effective coupling between EM fields and some tiny background torsion field.
The coupling is obtained after integrating out charged fermions, it is gauge
invariant and does not require the introduction of any new physics.Comment: 8 pages, LaTeX, one figure, enlarged version with minor correction
Applicability constraints of the Equivalence Theorem
In this work we study the applicability of the Equivalence Theorem, either
for unitary models or within an effective lagrangian approach. There are two
types of limitations: the existence of a validity energy window and the use of
the lowest order in the electroweak constants. For the first kind, we consider
some methods, based on dispersion theory or the large limit, that allow us
to extend the applicability. For the second, we have obtained numerical
estimates of the effect of neglecting higher orders in the perturbative
expansion.Comment: Final version to appear in Phys. Rev. D. Power counting and energy
range estimates have been refined, improved referencing. 4 postscript
figures, uses revtex. FT-UCM 1/9
On the Equivalence Theorem in the Description of the Symmetry Breaking Sector of the Standard Model
We develop an alternative formulation of the symmetry breaking sector of the
Standard Model as a gauged non-linear sigma model (NLSM) following the
philosophy of the Chiral lagrangian approach, which is the only compatible with
all the experimental and theoretical constraints. We derive the BRS symmetry of
the model and the corresponding quantum lagrangian, which is a generalization
of the standard Faddeev-Popov method, in a way which is covariant with respect
to the reparametrizations of the coset space of the NLSM. Then we use the BRS
invariance of the quantum lagrangian to state the Equivalence Theorem for the
renormalized -matrix elements calculated as a chiral expansion.Comment: LaTeX. Final version as it will appear in Nuclear Physics B (1994
LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector
We present a unified analysis of the two main production processes of vector
boson pairs at the LHC, VV-fusion and qqbar annihilation, in a minimal strongly
interacting electroweak symmetry breaking sector. Using a unitarized
electroweak chiral Lagrangian formalism and modeling the final V_L V_L strong
rescattering effects by a form factor, we describe qqbar annihilation processes
in terms of the two chiral parameters that govern elastic V_L V_L scattering.
Depending on the values of these two chiral parameters, the unitarized
amplitudes may present resonant enhancements in different angular
momentum-isospin channels. Scanning this two parameter space, we generate the
general resonance spectrum of a minimal strongly interacting electroweak
symmetry breaking sector and determine the regions that can be probed at the
LHC.Comment: Final version to appear in Phys. Rev. D, including a more detailed
exposition and a few more references. Conclusions and results unchanged. 14
pages, 5 figure
Branon radiative corrections to collider physics and precision observables
In the context of brane-world scenarios, we study the effects produced by the
exchange of virtual massive branons. A one-loop calculation is performed which
generates higher-dimensional operators involving SM fields suppressed by powers
of the brane tension scale. We discuss constraints on this scenario from
colliders such as HERA, LEP and Tevatron and prospects for future detections at
LHC or ILC. The most interesting phenomenology comes from new four-particles
vertices induced by branon radiative corrections, mainly from four fermion
interactions. The presence of flexible branes modifies also the muon anomalous
magnetic moment and the electroweak precision observables.Comment: 23 pages, 4 figures, LaTe
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