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Guido Marandella

Publications and source records attributed to Guido Marandella.

15 recordsLinked to original sources
arXiv2008

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.

hep-ph↗
arXiv2007

Mass Determination in SUSY-like Events with Missing Energy

We describe a kinematic method which is capable of determining the overall mass scale in SUSY-like events at a hadron collider with two missing (dark matter) particles. We focus on the kinematic topology in which a pair of identical particles is produced with each decaying to two leptons and an invisible particle (schematically, $pp\to YY+jets$ followed by each $Y$ decaying via $Y\to \ell X\to \ell\ell'N$ where $N$ is invisible). This topology arises in many SUSY processes such as squark and gluino production and decay, not to mention $t\anti t$ di-lepton decays. In the example where the final state leptons are all muons, our errors on the masses of the particles $Y$, $X$ and $N$ in the decay chain range from 4 GeV for 2000 events after cuts to 13 GeV for 400 events after cuts. Errors for mass differences are much smaller. Our ability to determine masses comes from considering all the kinematic information in the event, including the missing momentum, in conjunction with the quadratic constraints that arise from the $Y$, $X$ and $N$ mass-shell conditions. Realistic missing momentum and lepton momenta uncertainties are included in the analysis.

hep-ph↗
arXiv2007

Colored Unparticles

We examine a scenario where the new physics at the LHC includes an approximate conformal field theory, where some of the degrees of freedom (aka "unparticles") carry a color charge. We present a simple argument showing that the production cross section for scalar unparticles mediated by a gauge interaction is given by (2-d) times the standard particle expression, where d is the scaling dimension of the unparticle field. We explicitly check that this is indeed the case, which involves non trivial cancellations between different Feynman diagrams, for the process q qbar to scalar unparticles.

hep-ph↗
arXiv2006

The Gaugephobic Higgs

We present a class of models that contains Randall-Sundrum and Higgsless models as limiting cases. Over a wide range of the parameter space WW scattering is mainly unitarized by Kaluza-Klein partners of the W and Z, and the Higgs particle has suppressed couplings to the gauge bosons. Such a gaugephobic Higgs can be significantly lighter than the 114 GeV LEP bound for a standard Higgs, or heavier than the theoretical upper bound. These models predict a suppressed single top production rate and unconventional Higgs phenomenology at the LHC: the Higgs production rates will be suppressed and the Higgs branching fractions modified. However, the more difficult the Higgs search at the LHC is, the easier the search for other light resonances (like Z', W', t', exotic fermions) will be.

hep-ph↗
arXiv2006

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 $b_r$.

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arXiv2006

ElectroWeak precision data: the minimal set of parameters

We show how precision electroweak data, assuming CP conservation and flavor universality, despite being sensitive to 20 dimension 6 operators, constrain severely only 9 combinations of them. We define a set of 7 oblique parameters $\hat S, \hat T, \hat U, V, X,W,Y$ which fully describe corrections to the leptonic observables. We add two additional parameters $δε_q, δC_q$ to take into account the most precise hadronic observables. Another parameter $δε_b$ is considered for the bottom quark if flavor universality is not assumed for the third generation of quarks. We show that the approximation is extremely satisfactory testing it on a set of random new physics models and on some famous $Z'$ gauge bosons.

hep-ph↗
arXiv2005

The Super-little Higgs

Supersymmetry combined with little-Higgs can render the Higgs vev 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 no tree-level mass term to the Goldstone. The fermion representations are anomaly free, generation independent and embeddable into an SU(6) GUT. A simple mechanism provides the large top quark mass.

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arXiv2005

Little-Higgs corrections to precision data after LEP2

We reconsider little-Higgs corrections to precision data. In five models with global symmetries SU(5), SU(6), SO(9) corrections are (although not explicitly) of `universal' type. We get simple expressions for the Shat, That, W, Y parameters, which summarize all effects. In all models Shat > (W+Y)/2 and That, W, Y\ge 0. Results differ from previous analyses, which are sometimes incomplete, sometimes incorrect, and because we add LEP2 e ebar --> f fbar cross sections to the data set. Depending on the model the constraint on f ranges between 2 and 20 TeV. We next study the `simplest' little-Higgs model (and propose a new related model) which is not `universal' and affects precision data due to the presence of an extra Z' vector. By restricting the data-set to the most accurate leptonic data we show how corrections to precision data generated by a generic Z' can be encoded in four effective Shat, That, W, Y parameters, giving their expressions.

hep-ph↗
arXiv2005

Supersymmetry and precision data after LEP2

We study one loop supersymmetric corrections to precision observables. Adding LEP2 e ebar --> f fbar cross sections to the data-set removes previous hints for SUSY and the resulting constraints are in some cases stronger than direct bounds on sparticle masses. We consider specific models: split SUSY, CMSSM, gauge mediation, anomaly and radion mediation. Beyond performing a complete one-loop analysis, we also develop a simple approximation, based on the Shat, That, W, Y `universal' parameters. SUSY corrections give W,Y > 0 and mainly depend on the left-handed slepton and squark masses, on M_2 and on mu.

hep-ph↗
arXiv2004

Probing oscillations into sterile neutrinos with cosmology, astrophysics and experiments

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.

hep-ph↗
arXiv2004

Sterile neutrinos: from cosmology to experiments

We analyze the oscillation signals generated by one extra sterile neutrino. We fully take into account the effects of the established oscillations among active neutrinos. We analyze the effects in solar, atmospheric, reactor and beam experiments, cosmology and supernovæ. We analyze the impact of the LSND anomaly on cosmology showing, in the full 4 neutrino context, that it is not compatible with standard cosmology. We identify the still allowed regions of the parameter space, outlining which are the future experiments which can improve the bounds.

hep-ph↗
arXiv2003

Radiative Electroweak Symmetry Breaking from a Quasi-Localized Top Quark

We consider 5D supersymmetric SU(3) x SU(2) x U(1) theories compactified at the TeV scale on S^1/Z_2 with supersymmetry broken by boundary conditions. Localizing the top quark at a boundary of a fifth dimension by a bulk mass term M_t, reduces the strength of radiative electroweak symmetry breaking. For M_t R approximately 1--2, the natural value for the top and bottom squark masses are raised to 500--1200 GeV, and all other superpartners may have masses of the compactification scale, which has a natural range of 1/R ~= 1.5--3.5 TeV. The superpartner masses depend only on 1/R, and are precisely correlated amongst themselves and with the mass of the Higgs boson, which is lighter than 130 GeV.

hep-ph↗
arXiv2003

The Higgs mass as a function of the compactification scale

We calculate to a few percent precision the Higgs potential in a model with supersymmetry broken by boundary conditions on an extra-dimension, compactified to a segment of length $L$, and a top quark quasi-localized on one of the two boundaries. 1/L alone, in the range 2-4 TeV, determines the Higgs mass, in the range 110-125 GeV, and the spectrum of gauginos, higgsinos and of the third-generation squarks. Lower values of 1/L cannot be excluded, with a progressive delocalization of the top quark.

hep-ph↗
arXiv2002

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.

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