1,875 research outputs found
The good, the bad and the ugly .... of Horava gravity
I review the good, the bad and the ugly of the non-projectable versions of
Horava gravity. I explain how this non-relativistic theory was constructed and
why it was touted with such excitement as a quantum theory of gravity. I then
review some of the issues facing the theory, explaining how strong coupling
occurs and why this is such a problem for both phenomenology and the question
of renormalisability. Finally I comment on possible violations of Equivalence
Principle, and explain why these could be an issue for Blas et al's "healthy
extension". This paper was presented as a talk at PASCOS 2010 in Valencia.Comment: 7 page
Electroweak Limits on General New Vector Bosons
We study extensions of the Standard Model with general new vector bosons. The
full Standard Model gauge symmetry is used to classify the extra vectors and
constrain their couplings. We derive the corresponding effective Lagrangian,
valid at energies lower than the mass of the extra vectors, and use it to
extract limits from electroweak precision observables, including LEP 2 data. We
consider both universal and nonuniversal couplings to fermions. We study the
interplay of several extra vectors, which can have the effect of opening new
regions in parameter space. In particular, it allows to explain the anomaly in
the bottom forward-backward asymmetry with perturbative couplings. Finally, we
analyze quantitatively the implications for the Higgs mass.Comment: Latex 50 pages, 12 eps figures. Typos fixed, comments and references
adde
Impact of extra particles on indirect Z' limits
We study the possibility of relaxing the indirect limits on extra neutral
vector bosons by their interplay with additional new particles. They can be
systematically weakened, even below present direct bounds at colliders, by the
addition of more vector bosons and/or scalars designed for this purpose.
Otherwise, they appear to be robust.Comment: Latex 23 pages, 8 eps figures. Minor changes, version published in
Phys. Rev.
Looking for signals beyond the neutrino Standard Model
Any new neutrino physics at the TeV scale must include a suppression
mechanism to keep its contribution to light neutrino masses small enough. We
review some seesaw model examples with weakly broken lepton number, and comment
on the expected effects at large colliders and in neutrino oscillations.Comment: LaTeX 10 pages, 9 PS figures. Contribution to the Proceedings of the
XXXI International School of Theoretical Physics "Matter To The Deepest"
Ustron, Poland, September 5-11, 2007. Typos correcte
Experimental assessment of the speed of light perturbation in free-fall absolute gravimeters
Precision absolute gravity measurements are growing in importance, especially
in the context of the new definition of the kilogram. For the case of free-fall
absolute gravimeters with a Michelson-type interferometer tracking the position
of a free falling body, one of the effects that needs to be taken into account
is the speed of light perturbation due to the finite speed of propagation of
light. This effect has been extensively discussed in the past, and there is at
present a disagreement between different studies. In this work, we present the
analysis of new data and confirm the result expected from the theoretical
analysis applied nowadays in free-fall gravimeters. We also review the standard
derivations of this effect (by using phase shift or Doppler effect arguments)
and show their equivalence
Renormalization of gauge theories in the background-field approach
Using the background-field method we demonstrate the
Becchi-Rouet-Stora-Tyutin (BRST) structure of counterterms in a broad class of
gauge theories. Put simply, we show that gauge invariance is preserved by
renormalization in local gauge field theories whenever they admit a sensible
background-field formulation and anomaly-free path integral measure. This class
encompasses Yang-Mills theories (with possibly Abelian subgroups) and
relativistic gravity, including both renormalizable and non-renormalizable
(effective) theories. Our results also hold for non-relativistic models such as
Yang-Mills theories with anisotropic scaling or Horava gravity. They strengthen
and generalize the existing results in the literature concerning the
renormalization of gauge systems. Locality of the BRST construction is
emphasized throughout the derivation. We illustrate our general approach with
several explicit examples.Comment: 45 pages, no figures; references added, changes in the Introduction
and Conclusion
Renormalization of Horava Gravity
We prove perturbative renormalizability of projectable Horava gravity. The
key element of the argument is the choice of a gauge which ensures the correct
anisotropic scaling of the propagators and their uniform falloff at large
frequencies and momenta. This guarantees that the counterterms required to
absorb the loop divergences are local and marginal or relevant with respect to
the anisotropic scaling. Gauge invariance of the counterterms is achieved by
making use of the background-covariant formalism. We also comment on the
difficulties of this approach when addressing the renormalizability of the
non-projectable model.Comment: 35 pages, no figures; references discussing gauge invariance of
counterterms have been added, typos correcte
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