A New Custodian for a Realistic Higgsless Model

We present an example of a realistic Higgsless model that makes use of alternative $SU(2)_R$ assignments for the top and bottom quarks recently proposed by Agashe et al. which results in an enhanced custodial symmetry. Using these new representat ions reduces the deviations in the $Zb_\ell\bar{b}_\ell$ coupling to $\sim 4$ for a wide range of parameters, while this remaining correction can also be eliminated by varying the localization parameter (bulk mass) for $b_r$.Comment: 11 pages, 2 figure

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 d_s<2 or fermion unparticles with dimensions d_f<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.Comment: 26 pages, 1 figur

Superluminal neutrinos in long baseline experiments and SN1987a

Precise tests of Lorentz invariance in neutrinos can be performed using long baseline experiments such as MINOS and OPERA or neutrinos from astrophysical sources. The MINOS collaboration reported a measurement of the muonic neutrino velocities that hints to super-luminal propagation, very recently confirmed at 6 sigma by OPERA. We consider a general parametrisation which goes beyond the usual linear or quadratic violation considered in quantum-gravitational models. We also propose a toy model showing why Lorentz violation can be specific to the neutrino sector and give rise to a generic energy behaviour E^alpha, where alpha is not necessarily an integer number. Supernova bounds and the preferred MINOS and OPERA regions show a tension, due to the absence of shape distortion in the neutrino bunch in the far detector of MINOS. The energy independence of the effect has also been pointed out by the OPERA results.Comment: 22 pages, 7 figures; comment on Cherenkov emission added, version matching JHEP published pape

Curing the Ills of Higgsless Models: the S Parameter and Unitarity

We consider various constraints on Higgsless models of electroweak symmetry breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped space. First we show that the S parameter which is positive if fermions are localized on the Planck brane can be lowered (or made vanishing) by changing the localization of the light fermions. If the wave function of the light fermions is almost flat their coupling to the gauge boson KK modes will be close to vanishing, and therefore contributions to the S parameter will be suppressed. At the same time the experimental bounds on such Z' and W' gauge bosons become very weak, and their masses can be lowered to make sure that perturbative unitarity is not violated in this theory before reaching energies of several TeV. The biggest difficulty of these models is to incorporate a heavy top quark mass without violating any of the experimental bounds on bottom quark gauge couplings. In the simplest models of fermion masses a sufficiently heavy top quark also implies an unacceptably large correction to the Zb\bar{b} vertex and a large splitting between the KK modes of the top and bottom quarks, yielding large loop corrections to the T-parameter. We present possible directions for model building where perhaps these constraints could be obeyed as well.Comment: 21 pages, LaTeX, 5 figures. References and acknowledgements adde

Oblique Corrections from Higgsless Models in Warped Space

We calculate the tree-level oblique corrections to electroweak precision observables generated in higgless models of electroweak symmetry breaking with a 5D SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group on a warped background. In the absence of brane induced kinetic terms (and equal left and right gauge couplings) we find the S parameter to be ~1.15, while T,U~0, as in technicolor theories. Planck brane induced kinetic terms and unequal left-right couplings can lower S, however for sufficiently low values of S tree-level unitarity will be lost. A kinetic term localized on the TeV brane for SU(2)_D will generically increase S, however an induced kinetic term for U(1)_{B-L} on the TeV brane will lower S. With an appropriate choice of the value of this induced kinetic term S~0 can be achieved. In this case the mass of the lowest Z' mode will be lowered to about ~300 GeV.Comment: 18 pages, LaTeX, 2 figures include

Four tops on the real projective plane at LHC

We explore the four top signal ttbar ttbar at the 7 TeV Large Hadron Collider as a probe of physics beyond the standard model. Enhancement of the corresponding cross-section with respect to the Standard Model value can probe the electroweak symmetry breaking sector or test extra dimensional models with heavy Kaluza-Klein gluons and quarks. We perform a detailed analysis including background and detector simulation in the specific case of a universal extra-dimensional model with two extra dimensions compactified using the geometry of the real projective plane. For masses around 600 GeV, a discovery is possible for an effective cross section above 210 fb (36 fb) for 1/fb (10/fb) of integrated luminosity. This implies a branching ratio in tops of the (1,1) heavy photon above 13% (5%). Furthermore, the 4-top signal from the (2,0) and (0,2) tiers can be discovered with an integrated luminosity of 3.5/fb. The results of our simulation can be easily adapted to other models since the background processes are identical. Concerning the signal, typical production mechanisms for the ttbar ttbar signal are similar even if cross-section values may vary considerably depending on the model and the spectrum of the new particles.Comment: 26 pages, 4 figures, minor modifications and few references adde

A Dark Matter candidate from Lorentz Invariance in 6 Dimensions

We study the unique 6 dimensional orbifold with chiral fermions where a stable dark matter candidate is present due to Lorentz invariance on the orbifold, with no additional discrete symmetries imposed by hand. We propose a model of Universal Extra Dimensions where a scalar photon of few hundred GeV is a good candidate for dark matter. The spectrum of the model is characteristic of the geometry, and it has clear distinctive features compared to previous models of Kaluza-Klein dark matter. The 5 dimensional limit of this model is the minimal model of natural Kaluza-Klein dark matter. Notwithstanding the low mass range preferred by cosmology, the model will be a challenge for the LHC due to the relatively small splitting between the states in the same KK level.Comment: 37 pages, 6 figure