arXiv subjects

Veronica Sanz

Publications and source records attributed to Veronica Sanz.

At least 109 records · Page 6Linked to original sources

arXiv2012

It is a Graviton! or maybe not

The discovery of Kaluza-Klein (KK) gravitons is a smoking gun of extra dimensions. Other scenarios, however, could give rise to spin-two resonances of a new strongly-coupled sector and act as impostors. In this paper we prove that a spin-two resonance does not couple to the Standard Model through dimension-four operators. We then show that the massive graviton and its impostor both couple to the Standard Model through the same dimension-five operators. Therefore the spin determination is identical. Nevertheless, we also show that one can use the ratio of branching ratios to photons and to jets for distinguishing between KK gravitons and their impostors. The capacity to distinguish between KK gravitons and impostors is a manifestation of the breakdown of the duality between AdS and strongly-coupled theories.

hep-ph↗

arXiv2011

Distinguishing among Technicolor/Warped Scenarios in Dileptons

Models of dynamical electroweak symmetry breaking usually include new spin-1 resonances, whose couplings and masses have to satisfy electroweak precision tests. We propose to use dilepton searches to probe the underlying structure responsible for satisfying these. Using the invariant mass spectrum and charge asymmetry, we can determine the number, parity, and isospin of these resonances. We pick three models of strong/warped symmetry breaking, and show that each model produces specific features that reflect this underlying structure of electroweak symmetry breaking and cancellations.

hep-ph↗

arXiv2011

How Many Supersymmetries?

Supersymmetry in the gauge sector could be realized as N=1 or N=2 Supersymmetry, but the current LHC searches assume an N=1 realization. In this paper we show that squarks could be as light as few hundreds of GeV for N=2. We also describe an experimental procedure to count the number of supersymmetries, i.e. to distinguish between N=1 and N=2 supersymmetry, based on counting bins with different jet multiplicities and number of leptons.

hep-ph↗

arXiv2011

Non standard neutrino interactions at LEP2 and the LHC

We consider Non-Standard neutrino Interactions (NSI) connecting two neutrinos with two first-generation fermions ($e, u$ or $d$), which we assume to arise at at dimension eight due to New Physics. The coefficient is normalised as $4 εG_F/\sqrt{2}$. We explore signatures of NSI-on-electrons at LEP2, and of NSI-on-quarks at the LHC, treating the NSI as contact interactions at both energies. In models where the coefficients of dangerous dimension six operators are suppressed by cancellations, LEP2 provides interesting bounds on NSI operators ($ε\lsim 10^{-2} - 10^{-3}$), which arise because $\sqrt{s} \sim 200$ GeV, and the cancellation applied at zero momentum transfer. At the LHC, we use the Equivalence Theorem, which relates the longitudinal $W$ to the Higgs, to estimate the rate for $\bar{q} q W^+W^- e_α^+ e_β^-$ induced by NSI. We find that the cross-section is small, but that the outgoing particles have very high $p_T > 400$ GeV, which reduces the issue of backgrounds. In a conservative scenario, we find that the LHC at 14 TeV and with 100 fb$^{-1}$ of data would have a sensitivity to $ε\gsim 3 \times 10^{-3}$.

hep-ph↗

arXiv2011

Non-Standard Neutrino Interactions at Colliders

Many extensions of the Standard Model lead to non-standard neutrino interactions (NSI), which can affect the interpretation of current and future neutrino data. We explore an alternative approach to the study of these dimension eight four fermion interactions (of coefficient $4 εG_F/\sqrt{2}$), by bringing into play collider data. In models where coefficients of potential dimension six operators are suppressed by cancellations, LEP2 provides interesting bounds on NSI operators ($ε\lsim 10^{-2} - 10^{-3}$). If NSI are contact interactions at LHC energies, they induce an effective interaction $\bar{q} q W^+W^- e_\a^+ e_\b^-$(according to the Equivalence Theorem), to which the LHC at 14 TeV and with 100 fb$^{-1}$ of data has excellent sensitivity ($ε\gsim 3 \times 10^{-3}$).

hep-ph↗

arXiv2011

Toptet

Final states with four tops appear in various extensions of the Standard Model. Alas, top reconstruction faces combinatorial issues as they show up as large multiplicity events. In this paper, we present a new procedure to determine whether new physics is in fact due to a new source for tops. We establish the use of this procedure to separate the signal from background (primarily $t\bar{t}$+jets). Our analysis is model independent, in that it does not use any details of the four top production (such as possible missing energy), and does not require b-tagging.

hep-ph↗

arXiv2011

Simplified Models for LHC New Physics Searches

This document proposes a collection of simplified models relevant to the design of new-physics searches at the LHC and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the "Topologies for Early LHC Searches" workshop, held at SLAC in September of 2010, the purpose of which was to develop a set of representative models that can be used to cover all relevant phase space in experimental searches. Particular emphasis is placed on searches relevant for the first ~50-500 pb-1 of data and those motivated by supersymmetric models. This note largely summarizes material posted at http://lhcnewphysics.org/, which includes simplified model definitions, Monte Carlo material, and supporting contacts within the theory community. We also comment on future developments that may be useful as more data is gathered and analyzed by the experiments.

hep-ph↗

arXiv2011

Pseudo-Dirac Dark Matter Leaves a Trace

Pseudo-Dirac Dark Matter is a viable type of dark matter which originates from a new Dirac fermion whose two Weyl states get slightly split in mass by a small Majorana term. The decay of the heavier to the lighter state naturally occurs over a detectable length scale. Thus, whenever pseudo-Dirac Dark Matter is produced in a collider, it leaves a clear trace: a visible displaced vertex in association with missing energy. Moreover, pseudo-Dirac Dark Matter behaves Dirac-like for relic abundance and Majorana-like in direct detection experiments: it has efficient s-wave annihilations but it lacks of dangerous vector interactions with the quarks in the nuclei. We provide a general treatment using an effective field theory approach, then specializing to the supersymmetric situation of a pseudo-Dirac Bino. The dark matter mass and the mass splitting can be extracted from measurements of the decay length and the invariant mass of the products, even in presence of missing energy.

hep-ph↗

arXiv2009

Mass-Matching in Higgsless

Modern extra-dimensional Higgsless scenarios rely on a mass-matching between fermionic and bosonic KK resonances to evade constraints from precision electroweak measurements. After analyzing all of the Tevatron and LEP bounds on these so-called Cured Higgsless scenarios, we study their LHC signatures and explore how to identify the mass-matching mechanism, the key to their viability. We find singly and pair produced fermionic resonances show up as clean signals with 2 or 4 leptons and 2 hard jets, while neutral and charged bosonic resonances are visible in the dilepton and leptonic WZ channels, respectively. A measurement of the resonance masses from these channels shows the matching necessary to achieve $S\simeq 0$. Moreover, a large single production of KK-fermion resonances is a clear indication of compositeness of SM quarks. Discovery reach is below 10 fb$^{-1}$ of luminosity for resonances in the 700 GeV range.

hep-ph↗

arXiv2009

Leptogenic Supersymmetry

Leptogenic supersymmetry is a scenario characterized by cascade decays with copious lepton production. Leptogenic models have striking signatures that can be probed by the LHC even in the 10 TeV run with as little as 200 pb^-1 of data, provided the squark masses are about 1 TeV. Leptogenic supersymmetry spectrum arises in several well-motivated models and its signatures are long-lived sleptons, numerous isolated leptons, abundant Higgs production, rather energetic jets, and no missing energy. The Higgs can be discovered in the h->b bbar mode via the 4 leptons+4 jets channel because the leptons accompanying Higgs production suppress the background. The superparticle masses in leptogenic supersymmetry can be measured efficiently due to lack of missing energy and high lepton multiplicity. We estimate that 1 fb^-1 of integrated luminosity is sufficient to determine the light Higgs, neutralinos, charginos, slepton, sneutrino and squark masses in a 14 TeV run.

hep-ph↗

arXiv2008

Describing viable technicolor scenarios

We construct an effective lagrangian for new strong interactions at the LHC, including as a first step the two lightest triplets of spin-1 resonances. Our parametrization is general enough to allow for previously unstudied spectrum and couplings. Among available frameworks to describe the spin-1 sector, we rely on an extra-dimensional description. Our approach limits the number of parameters, yet is versatile enough to describe the phenomenology of a wide range of new scenarios of strong electroweak symmetry breaking.

hep-ph↗

arXiv2007

The fifth dimension as an analogue computer for strong interactions at the LHC

We present a mechanism to get S ~ 0 or even negative, without bringing into play the SM fermion sector. This mechanism can be applied to a wide range of 5D models, including composite Higgs and Higgsless models. As a realization of the mechanism we introduce a simple model, although the effect on S does not rely on the underlying dynamics generating the background. Models that include this mechanism enjoy the following features: weakly-coupled light resonances (as light as 600 GeV) and degenerate or inverted resonance spectrum.

hep-ph↗

arXiv2007

(Not) Summing over Kaluza-Kleins

Models in extra-dimensions have unique features. Many of their surprising properties simply result from the underlying 5D structure. This structure shows up as ``Sum Rules'' involving the whole tower of Kaluza-Kleins. In this paper, we present a holographic shortcut and derive these results without solving the eigenvalue problem: we express 4D physical quantities directly in terms of the 5D metric. In warped space, one can go further and isolate the effect of the new physics sector. This method can be used for any 5D model, and we apply it here to the case of holographic QCD and technicolor.

hep-ph↗

arXiv2006

A negative S parameter from Holographic Technicolor

We present a new class of 5D models, Holographic Technicolor, which fulfills the basic requirements for a candidate of comprehensible 4D strong dynamics at the electroweak scale. It is the first Technicolor-like model able to provide a vanishing or even negative tree-level S parameter, avoiding any no-go theorem on its sign. The model is described in the large-N regime. S is therefore computable: possible corrections coming from boundary terms follow the 1/N suppression, and generation of fermion masses and the S parameter issue do split up. We investigate the model's 4D dual, probably walking Technicolor-like with a large anomalous dimension.

hep-ph↗

arXiv2006

Geometric approach to condensates in holographic QCD

An SU(Nf)xSU(Nf) Yang-Mills theory on an extra-dimensional interval is considered, with appropriate symmetry-breaking boundary conditions on the IR brane. UV-brane to UV-brane correlators at high energies are compared with the OPE of two-point functions of QCD quark currents. Condensates correspond to departure from AdS of the (different) metrics felt by vector and axial combinations, away from the UV brane. Their effect on hadronic observables is studied: the extracted condensates agree with the signs and orders of magnitude expected from QCD.

hep-ph↗

arXiv2006

The A5 and the pion field

In this talk, an SU(Nf)xSU(Nf)Yang-Mills model with a compact extra-dimension is used to describe the spin-1 mesons and pions of massless QCD in the large-Nc. The right 4D symmetry and symmetry-breaking pattern is produced by imposing appropriate boundary conditions. The Goldstone boson fields are constructed using a Wilson line. We derive the low-energy limit (chiral lagrangian), discuss rho-meson dominance, sum rules between resonance couplings and the relation with the QCD high-energy behavior. Finally, we provide an analytic expression for the two-point function of vector and axial currents.

hep-ph↗

arXiv2006

Interpolating between low and high energy QCD via a 5D Yang-Mills model

We describe the Goldstone bosons of massless QCD together with an infinite number of spin-1 mesons. The field content of the model is SU(Nf)xSU(Nf) Yang-Mills in a compact extra-dimension. Electroweak interactions reside on one brane. Breaking of chiral symmetry occurs due to the boundary conditions on the other brane, away from our world, and is therefore spontaneous. Our implementation of the holographic recipe maintains chiral symmetry explicit throughout. For intermediate energies, we extract resonance couplings. These satisfy sum rules due to the 5D nature of the model. These sum rules imply, when taking the high energy limit, that perturbative QCD constraints are satisfied. We also illustrate how the 5D model implies a definite prescription for handling infinite sums over 4D resonances. Taking the low energy limit, we recover the chiral expansion and the corresponding non-local order parameters. All local order parameters are introduced separately.

hep-ph↗

arXiv2004

Supersymmetry Breaking and Restoration in the Interval

We study fermions, such as gravitinos and gauginos in supersymmetric theories, propagating in a five-dimensional bulk where the fifth dimension is an interval. We show the mass spectrum becomes independent from the Scherk-Schwarz parameter if the boundary mass terms obey a relation of alignment with the bulk supersymmetry breaking.

hep-th↗