A Way to Dynamically Overcome the Cosmological Constant Problem

The Cosmological Constant problem can be solved once we require that the full standard Einstein Hilbert lagrangian, gravity plus matter, is multiplied by a total derivative. We analyze such a picture writing the total derivative as the covariant gradient of a new vector field (b_mu). The dynamics of this b_mu field can play a key role in the explanation of the present cosmological acceleration of the Universe.Comment: 5 page

Particle Currents in a Space-Time dependent and CP-violating Higgs Background: a Field Theory Approach

Motivated by cosmological applications like electroweak baryogenesis, we develop a field theoretic approach to the computation of particle currents on a space-time dependent and CP-violating Higgs background. We consider the Standard Model model with two Higgs doublets and CP violation in the scalar sector, and compute both fermionic and Higgs currents by means of an expansion in the background fields. We discuss the gauge dependence of the results and the renormalization of the current operators, showing that in the limit of local equilibrium, no extra renormalization conditions are needed in order to specify the system completely.Comment: 21 pages, LaTeX file, uses epsf.sty. 4 figures available as a compressed .ep

Hairy black holes in theories with massive gravitons

This is a brief survey of the known black hole solutions in the theories of ghost-free bigravity and massive gravity. Various black holes exist in these theories, in particular those supporting a massive graviton hair. However, it seems that solutions which could be astrophysically relevant are the same as in General Relativity, or very close to them. Therefore, the no-hair conjecture essentially applies, and so it would be hard to detect the graviton mass by observing black holes.Comment: References added. 20 pages, 3 figures, based on the talk given at the 7-th Aegean Summer School "Beyond Einstein's theory of gravity", September 201

Information and Discrimination from b Quark Production on Z Resonance

We introduce and define operatively in a model independent way a new ``heavy" b-vertexparameter, $\eta_b$, that can be derived from the measurement of a special polarization asymmetry for production of b-quarks on Z resonance. We show that the combination of the measurement of $\eta_b$ with that of a second and previously defined ``heavy" b-vertex parameter $\delta_{bV}$ can discriminate a number of models of New Physics that remain associated to different ``trajectories" in the plane of the variations of the two parameters. This is shown in particular for some popular SUSY and technicolor-type models. In general, this discrimination is possible if a measurement of \underline{both} parameters is performed.Comment: 22 pages, 6 figures available by air mail upon request, (e-mail [email protected] PM/94-04, UTS-DFT-94-02 .( revised version with corrected references

On the Importance of Electroweak Corrections for Majorana Dark Matter Indirect Detection

Recent analyses have shown that the inclusion of electroweak corrections can alter significantly the energy spectra of Standard Model particles originated from dark matter annihilations. We investigate the important situation where the radiation of electroweak gauge bosons has a substantial influence: a Majorana dark matter particle annihilating into two light fermions. This process is in p-wave and hence suppressed by the small value of the relative velocity of the annihilating particles. The inclusion of electroweak radiation eludes this suppression and opens up a potentially sizeable s-wave contribution to the annihilation cross section. We study this effect in detail and explore its impact on the fluxes of stable particles resulting from the dark matter annihilations, which are relevant for dark matter indirect searches. We also discuss the effective field theory approach, pointing out that the opening of the s-wave is missed at the level of dimension-six operators and only encoded by higher orders.Comment: 25 pages, 6 figures. Minor corrections to match version published in JCA

Thermal Stability of Corrugated Epitaxial Graphene Grown on Re(0001)

We report on a novel approach to determine the relationship between the corrugation and the thermal stability of epitaxial graphene grown on a strongly interacting substrate. According to our density functional theory calculations, the C single layer grown on Re(0001) is strongly corrugated, with a buckling of 1.6 angstrom, yielding a simulated C 1s core level spectrum which is in excellent agreement with the experimental one. We found that corrugation is closely knit with the thermal stability of the C network: C-C bond breaking is favored in the strongly buckled regions of the moire cell, though it requires the presence of diffusing graphene layer vacancies

Fermion scattering off electroweak phase transition kink walls with hypermagnetic fields

We study the scattering of fermions off a finite width kink wall during the electroweak phase transition in the presence of a background hypermagnetic field. We derive and solve the Dirac equation for such fermions and compute the reflection and transmission coefficients for the case when the fermions move from the symmetric to the broken symmetry phase. We show that the chiral nature of the fermion coupling with the background field in the symmetric phase generates an axial asymmetry in the scattering processes. We discuss possible implications of such axial charge segregation for baryon number generation.Comment: 9 pages, 3 Postscript figures, uses RevTeX4. Expanded discussion, published versio

A No-Lose Theorem for Higgs Searches at a Future Linear Collider

Assuming perturbativity up to a high energy scale $\sim 10^{16}$ GeV, we demonstrate that a future $e^+e^-$ linear collider operating at $\sqrt{s} =$ 500 GeV with $\int{\cal L}=$ 500 fb$^{-1}$ per year (such as the recently proposed TESLA facility) will detect a Higgs boson signal regardless of the complexity of the Higgs sector and of how the Higgs bosons decay.Comment: 4 pages, LaTe

The abundance of relativistic axions in a flaton model of Peccei-Quinn symmetry

Flaton models of Peccei-Quinn symmetry have good particle physics motivation, and are likely to cause thermal inflation leading to a well-defined cosmology. They can solve the $\mu$ problem, and generate viable neutrino masses. Canonical flaton models predict an axion decay constant F_a of order 10^{10} GeV and generic flaton models give F_a of order 10^9 GeV as required by observation. The axion is a good candidate for cold dark matter in all cases, because its density is diluted by flaton decay if F_a is bigger than 10^{12} GeV. In addition to the dark matter axions, a population of relativistic axions is produced by flaton decay, which at nucleosynthesis is equivalent to some number \delta N_\nu of extra neutrino species. Focussing on the canonical model, containing three flaton particles and two flatinos, we evaluate all of the flaton-flatino-axion interactions and the corresponding axionic decay rates. They are compared with the dominant hadronic decay rates, for both DFSZ and KSVZ models. These formulas provide the basis for a precise calculation of the equivalent \delta N_\nu in terms of the parameters (masses and couplings). The KSVZ case is probably already ruled out by the existing bound \delta N_\nu\lsim 1. The DFSZ case is allowed in a significant region of parameter space, and will provide a possible explanation for any future detection of nonzero $\delta N_\nu$