arXiv subjects

Antonio Delgado

Publications and source records attributed to Antonio Delgado.

71 records · Page 4Linked to original sources

arXiv2011

A Light Scalar in Low-Scale Technicolor

In addition to the narrow spin-one resonances $ρ_T$, $ω_T$ and $a_T$ occurring in low-scale technicolor, there will be relatively narrow scalars in the mass range 200 to 600--700 GeV. We study the lightest isoscalar state, $σ_T$. In several important respects it is like a heavy Higgs boson with a small vev. It may be discovered with high luminosity at the LHC where it is produced via weak boson fusion and likely has substantial $W^+ W^-$ and $Z^0Z^0$ decay modes.

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arXiv2010

A Gauge-Mediated Embedding of the S-MSSM

We embed the S-MSSM -- a singlet extension of the minimal supersymmetric standard model with an explicit mu-term and supersymmetric mass term -- in a gauge-mediated supersymmetry breaking scheme. We find that by absolving the singlet of its responsibility for solving the mu-problem, we are instead able to solve the little hierarchy problem naturally. Specifically, we find that even with a minimal embedding of the S-MSSM into a gauge-mediated scheme, we can easily raise the lightest Higgs mass above 114 GeV, while keeping top squarks below the TeV scale, maintaining perturbative unification of the gauge couplings, and without tuning the other parameters of the model.

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arXiv2010

The SUSY Higgs Mass: the Singlet Saves the Day

We present a generalization of the Next-to-Minimal Supersymmetric Standard Model (NMSSM), with an explicit mu-term and a supersymmetric mass for the singlet superfield, as a route to alleviating the little hierarchy problem of the Minimal Supersymmetric Standard Model (MSSM). Though this model does not address the mu-problem of the MSSM, we are able to generate masses for the lightest neutral Higgs boson up to 140 GeV with top squarks below the TeV scale, all couplings perturbative to the gauge unification scale, and with no need to fine tune parameters in the scalar potential. This model, which we call the S-MSSM, more closely resembles the MSSM phenomenologically than the NMSSM as usually defined.

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arXiv2009

A Simple-Minded Unitarity Constraint and an Application to Unparticles

Unitarity, a powerful constraint on new physics, has not always been properly accounted for in the context of hidden sectors. Feng, Rajaraman and Tu have suggested that large (pb to nb) multi-photon or multi-lepton sugnals could be generated at the LHC through the three-point functions of a conformally-invariant hidden sector (an "unparticle" sector.) Because of the conformal invariance, the kinematic distributions are calculable. However, the cross-sections for many such processes grow rapidly with energy, and at some high scale, to preserve unitarity, conformal invariance must break down. Requiring that conformal invariance not be broken, and that no signals be already observed at the Tevatron, we obtain a strong unitarity bound on multi-photon events at the (10 TeV) LHC. For the model of Feng et al., even with extremely conservative assumptions, cross-sections must be below 25 fb, and for operator dimension near 2, well below 1 fb. In more general models, four-photon signals could still reach cross-sections of a few pb, though bounds below 200 fb are more typical. Our methods apply to a wide variety of other processes and settings.

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arXiv2009

Fermion Mass Hierarchy from the Soft Wall

We develop a 5d model for ElectroWeak physics based on a non compact warped extra dimension of finite length, known as the soft wall scenario, where all the dynamical degrees of freedom propagate in the 5d bulk. We solve the equations of motion and find the allowed spectra, showing that the mass of the lightest fermionic mode behaves as a power law of the effective 4d Yukawa coupling constant, with the exponent being the corresponding fermionic 5d bulk mass. Precisely this non universal behavior allows us to reproduce the hierarchy between the Standard Model (SM) fermion masses (from neutrinos to the top quark) with non-hierarchical fermionic bulk masses.

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arXiv2007

Hunting long-lived gluinos at the Pierre Auger Observatory

Eventual signals of split sypersymmetry in cosmic ray physics are analyzed in detail. The study focusses particularly on quasi-stable colorless R-hadrons originating through confinement of long-lived gluinos (with quarks, anti-quarks, and gluons) produced in pp collisions at astrophysical sources. Because of parton density requirements, the gluino has a momentum which is considerable smaller than the energy of the primary proton, and so production of heavy (mass ~ 500 GeV) R-hadrons requires powerful cosmic ray engines able to accelerate particles up to extreme energies, somewhat above 10^{13.6} GeV. Using a realistic Monte Carlo simulation with the AIRES engine, we study the main characteristics of the air showers triggered when one of these exotic hadrons impinges on a stationary nucleon of the Earth atmosphere. We show that R-hadron air showers present clear differences with respect to those initiated by standard particles. We use this shower characteristics to construct observables which may be used to distinguish long-lived gluinos at the Pierre Auger Observatory.

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arXiv2007

Unparticles-Higgs Interplay

We show that scalar unparticles coupled to the Standard Model Higgs at the renormalizable level can have a dramatic impact in the breaking of the electroweak symmetry already at tree level. In particular one can get the proper electroweak scale without the need of a Higgs mass term in the Lagrangian. By studying the mixed unparticle-Higgs propagator and spectral function we also show how unparticles can shift the Higgs mass away from its Standard Model value, λv^2, and influence other Higgs boson properties. Conversely, we study in some detail how electroweak symmetry breaking affects the unparticle sector by breaking its conformal symmetry and generating a mass gap. We also show that, for Higgs masses above that gap, unparticles can increase quite significantly the Higgs width.

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arXiv2007

Electroweak observables in a general 5D background

Warped extra dimensions provide a new playground to study electroweak brea-king and the nature of the higgs field. In this paper we reanalyze the electroweak observables in theories with one extra dimension and a completely general warp factor. We demonstrate that, regardless of the 5D background, SU(2)_R is needed in order to avoid excessive contributions to the T parameter. For higgsless theories cancelations between different contributions to the S parameter are needed.

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arXiv2006

A Fat Higgs with a Fat Top

A new variant of the supersymmetric Fat Higgs model is presented in which the MSSM Higgses as well as the top quark are composite. The underlying theory is an s-confining SU(3) gauge theory with the MSSM gauge groups realized as gauged sub-groups of the chiral flavor symmetries. This motivates the large Yukawas necessary for the large top mass and SM-like Higgs of mass>>M_Z in a natural way as the residual of the strong dynamics responsible for the composites. This removes fine-tuning associated with these couplings present in the original Fat Higgs and New Fat Higgs models, respectively.

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arXiv2006

Splitting Extended Supersymmetry

We show how splitting supersymmetry reconciles a class of intersecting brane models with unification. The gauge sector in these models arises in multiplets of extended supersymmetry while matter states are in N=1 representations. A deformation of the angles between the branes gives large masses to squarks and sleptons, as well as supersymmetry breaking contributions to other string states. The latter generate at one-loop heavy Dirac masses for Winos and gluinos and can induce a mass term for the Higgsino doublets. We find that this scenario is compatible with gauge coupling unification at high scale for both cases where the gauge sector is N=2 and N=4 supersymmetric. Moreover a neutralino, combination of neutral Higgsinos and Binos, is a natural candidate for dark matter.

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arXiv2004

Warped Fermions and Precision Tests

We analyze the behavior of Standard Model matter propagating in a slice of AdS_5 in the presence of infrared-brane kinetic terms. Brane kinetic terms are naturally generated through radiative corrections and can also be present at tree level. The effect of the brane kinetic terms is to expell the heavy KK modes from the infrared-brane, and hence to reduce their coupling to the localized Higgs field. In a previous work we showed that sizable gauge kinetic terms can allow KK mode masses as low as a few TeV, compatible with present precision measurements. We study here the effect of fermion brane kinetic terms and show that they ameliorate the behavior of the theory for third generation fermions localized away from the infrared brane, reduce the contribution of the third generation quarks to the oblique correction parameters and mantain a good fit to the precision electroweak data for values of the KK masses of the order of the weak scale.

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arXiv2004

Raising the Higgs Mass in Supersymmetric Models

The minimal supersymmetric standard model, and extensions, predicts a relatively light higgs particle if one supposes perturbativity until high scales. That fact is in conflict with nowadays data coming from LEPII fruitless searches for the Higgs boson. This bound is sufficient to rule out a big portion of the parameter space of the MSSM. In this letter we propose two mechanism of raising the higgs mass at tree level, thus not needing very heavy sparticles that would reintroduce some fine-tuning in the problem.

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arXiv2004

Running into New Territory in SUSY Parameter Space

The LEP-II bound on the light Higgs mass rules out the vast majority of parameter space left to the Minimal Supersymmetric Standard Model (MSSM) with weak-scale soft-masses. This suggests the importance of exploring extensions of the MSSM with non-minimal Higgs physics. In this article, we explore a theory with an additional singlet superfield and an extended gauge sector. The theory has a number of novel features compared to both the MSSM and Next-to-MSSM, including easily realizing a light CP-even Higgs mass consistent with LEP-II limits, tan(beta) < 1, and a lightest Higgs which is charged. These features are achieved while remaining consistent with perturbative unification and without large stop-masses. Discovery modes at the Tevatron and LHC are discussed.

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arXiv2004

The Higgs Mass Bound in Gauge Extensions of the Minimal Supersymmetric Standard Model

The minimal supersymmetric standard model, and extensions, have stringent upper bounds on the mass of the lightest Higgs boson if perturbativity up to the Planck scale is assumed. We argue that these bounds are softened tremendously if the Higgs is charged under an asymptotically free gauge group. We present a model with an additional SU(2) gauge group which easily produces Higgs masses above 200 GeV while avoiding electroweak constraints. If one allows some fine-tuning of the high-scale value of the gauge coupling, Higgs masses greater than 350 GeV are achieved. Unification of couplings is predicted to similar accuracy as in the minimal supersymmetric standard model with only small deviations at the two-loop level.

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arXiv2003

RS1, Custodial Isospin and Precision Tests

We study precision electroweak constraints within a RS1 model with gauge fields and fermions in the bulk. The electroweak gauge symmetry is enhanced to SU(2)_L \times SU(2)_R \times U(1)_{B-L}, thereby providing a custodial isospin symmetry sufficient to suppress excessive contributions to the T parameter. We then construct complete models, complying with all electroweak constraints, for solving the hierarchy problem, without supersymmetry or large hierarchies in the fundamental couplings. Using the AdS/CFT correspondence our models can be interpreted as dual to a strongly coupled conformal Higgs sector with global custodial symmetry, gauge and fermionic matter being fundamental fields external to the CFT. This scenario has interesting collider signals, distinct from other RS models in the literature.

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arXiv2003

Precision Electroweak Data and Unification of Couplings in Warped Extra Dimensions

Warped extra dimensions allow a novel way of solving the hierarchy problem, with all fundamental mass parameters of the theory naturally of the order of the Planck scale. The observable value of the Higgs vacuum expectation value is red-shifted, due to the localization of the Higgs field in the extra dimension. It has been recently observed that, when the gauge fields propagate in the bulk, unification of the gauge couplings may be achieved. Moreover, the propagation of fermions in the bulk allows for a simple solution to potentially dangerous proton decay problems. However, bulk gauge fields and fermions pose a phenomenological challenge, since they tend to induce large corrections to the precision electroweak observables. In this article, we study in detail the effect of gauge and fermion fields propagating in the bulk in the presence of gauge brane kinetic terms compatible with gauge coupling unification, and we present ways of obtaining a consistent description of experimental data, while allowing values of the first Kaluza Klein mode masses of the order of a few TeV.

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arXiv2002

Grand Unification in RS1

We study unification in the Randall-Sundrum scenario for solving the hierarchy problem, with gauge fields and fermions in the bulk. We calculate the one-loop corrected low-energy effective gauge couplings in a unified theory, broken at the scale M_GUT in the bulk. We find that, although this scenario has an extra dimension, there is a robust (calculable in the effective field theory) logarithmic dependence on M_GUT, strongly suggestive of high-scale unification, very much as in the (4D) Standard Model. Moreover, bulk threshold effects are naturally small, but volume-enhanced, so that we can accommodate the measured gauge couplings. We show in detail how excessive proton decay is forbidden by an extra U(1) bulk gauge symmetry. This mechanism requires us to further break the unified group using boundary conditions. A 4D dual interpretation, in the sense of the AdS/CFT correspondence, is provided for all our results. Our results show that an attractive unification mechanism can combine with a non-supersymmetric solution to the hierarchy problem.

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