Guido Marandella

A GIM mechanism from extra dimensions

We explore how to protect extra dimensional models from large avor changing neutral currents by using bulk and brane avor symmetries. We show that a GIM mechanism can be built in to warped space models such as Randall-Sundrum or composite Higgs models if avor mixing is introduced via UV brane kinetic mixings for right handed quarks. We give a realistic implementation both for a model with minimal avor violation and one with next-to-minimal avor violation. The latter does not suer from a CP problem. We consider some of the existing experimental constraints on these models implied by precision electroweak tests.

Probing oscillations into sterile neutrinos with cosmology, astrophysics and experiments

Abstract We perform a thorough analysis of oscillation signals generated by one extra sterile neutrino, extending previous analyses done in simple limiting cases and including the effects of established oscillations among active neutrinos. We consider the following probes: solar, atmospheric, reactor and beam neutrinos, big-bang nucleosynthesis (helium-4, deuterium), cosmic microwave background, large scale structure, supernovae, neutrinos from other astrophysical sources. We find no evidence for a sterile neutrino in present data, identify the still allowed regions, and study which future experiments can best probe them: sub-MeV solar experiments, more precise studies of CMB or BBN, future supernova explosions, etc. We discuss how the LSND hint is strongly disfavoured by the constraints of (standard) cosmology.

A New Custodian for a Realistic Higgsless Model

We present an example of a realistic Higgsless model that makes use of alternative SU(2){sub R} assignments for the top and bottom quarks recently proposed by Agashe et al. which results in an enhanced custodial symmetry. Using these new representations reduces the deviations in the Zb{sub l}b{sub l} coupling to {approx}4% for a wide range of parameters, while this remaining correction can also be eliminated by varying the localization parameter (bulk mass) for b{sub r}.

The super-little Higgs

Supersymmetry combined with little Higgs can render the Higgs vacuum expectation value super-little, providing models of electroweak symmetry breaking free from fine-tunings. We discuss the difficulties that arise in implementing this idea and propose one simple successful model. Thanks to appropriately chosen Higgs representations, D-terms give a negligible tree-level mass term to the Goldstone. The fermion representations are anomaly free, generation independent, and embeddable into an SU(6) grand unified theory. A simple mechanism provides the large top quark mass.

The AdS/CFT/unparticle correspondence

We examine the correspondence between the anti-de Sitter (AdS) description of conformal field theories (CFTs) and the unparticle description of CFTs. We show how unparticle actions are equivalent to holographic boundary actions for fields in AdS, and how massive unparticles provide a new type of infrared cutoff that can be simply implemented in AdS by a soft breaking of conformal symmetry. We also show that processes involving scalar unparticles with dimensions ds < 2 or fermion unparticles with dimensions df < 5/2 are insensitive to ultraviolet cutoff effects. Finally we show that gauge interactions for unparticles can be described by bulk gauge interactions in AdS and that they correspond to minimal gauging of the non-local effective action, and we compute the fermion unparticle production cross-section.

Breaking the electroweak symmetry and supersymmetry by a compact extra dimension

We revisit in some more detail a recent specific proposal for the breaking of the electroweak symmetry and of supersymmetry by a compact extra dimension. Possible mass terms for the Higgs and the matter hypermultiplets are considered and their effects on the spectrum analyzed. Previous conclusions are reinforced and put on firmer ground.

Dimensions of supersymmetric operators from AdS/CFT

We examine the AdS/CFT correspondence through a manifestly 5D supersymmetric formalism, corresponding to a 4D = 1 supersymmetric CFT. We find that the dimensions of scalar and fermionic component operators are simply related, and that there is a smooth transition of scalar operator dimensions through the value ds = 2. By using this formalism, we also show that the formula used in the string literature for the dimension of fermion operators is incomplete.

Relating the electroweak scale to an extra dimension: Constraints from electroweak precision tests

In models with supersymmetry breaking by boundary conditions on an extra-dimension it is possible to relate in a quantitative natural way the Fermi scale to the size of the extra-dimension. We analyze in detail the compatibility of such models with ElectroWeak Precision Tests.