arXiv subjects

Manuel Perez-Victoria

Publications and source records attributed to Manuel Perez-Victoria.

18 recordsLinked to original sources

arXiv2026

Gauge theories from scattering amplitudes with minimal assumptions

We revisit the emergence of a Yang-Mills symmetry in theories with massless spin 1 particles from fundamental physical properties of scattering amplitudes. In the standard proofs, some symmetry and reality properties of the coupling constants in three-point amplitudes are assumed. These properties cannot be justified using only three-point amplitudes but we show that they arise as consequences of the consistent factorization of four-particle amplitudes, for particular choices of the particle basis. This applies to self-interactions of massless spin 1 particles and also to their interactions with spin 0 and 1/2 particles. CP invariance is a derived property, not an additional assumption. The situation for gravity interactions is analogous and it is dealt with in the same fashion.

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arXiv2025

Vector-like quarks with non-renormalizable interactions

We study the impact of the leading non-renormalizable terms in the effective field theory that describes general extensions of the Standard Model with vector-like quarks. Dropping the usual assumption of renormalizability has several phenomenological consequences for the production and decay of the heavy quarks and also for Higgs physics. The most dramatic effects, including those associated with a long lifetime, occur for vector-like quarks with non-standard quantum numbers.

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arXiv2025

A complete effective field theory for dark matter

We present an effective field theory describing the relevant interactions of the Standard Model with an electrically neutral particle that can account for the dark matter in the Universe. The possible mediators of these interactions are assumed to be heavy. The dark matter candidates that we consider have spin 0, 1/2 or 1, belong to an electroweak multiplet with arbitrary isospin and hypercharge and their stability at cosmological scales is guaranteed by imposing a $\mathbb{Z}_2$ symmetry. We present the most general framework for describing the interaction of the dark matter with standard particles, and construct a general non-redundant basis of the gauge-invariant operators up to dimension six. The basis includes multiplets with non-vanishing hypercharge, which can also be viable DM candidates. We give two examples illustrating the phenomenological use of such a general effective framework. First, we consider the case of a scalar singlet, provide convenient semi-analytical expressions for the relevant dark matter observables, use present experimental data to set constraints on the Wilson coefficients of the operators, and show how the interplay of different operators can open new allowed windows in the parameter space of the model. Then we study the case of a lepton isodoublet, which involves co-annihilation processes, and we discuss the impact of the operators on the particle mass splitting and direct detection cross sections. These examples highlight the importance of the contribution of the various non-renormalizable operators, which can even dominate over the gauge interactions in certain cases.

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arXiv2024

Undecay

Unstable particles decay sooner or later, so they are not described by asymptotic one-particle states and they should not be included as independent states in unitarity relations such as the optical theorem. The same applies to any countable collection of unstable particles. We show that the behaviour of unparticle stuff, that is, a continuous collection of particles with different masses and common decay channels, is pretty different: it has a non-vanishing probability of surviving for ever and the corresponding asymptotic states must be taken into account to comply with unitarity. We also discuss compressed spectra and the transition from the discrete to the continuous case.

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arXiv2019

Field redefinitions in effective theories at higher orders

The invariance of physical observables under redefinitions of the quantum fields is a well-known and important property of quantum field theory. We study perturbative field redefinitions in effective theories, paying special attention to higher-order effects and their impact on matching to an ultraviolet theory at the classical and quantum levels.

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arXiv2015

Observable Effects of General New Scalar Particles

We classify all possible new scalar particles that can have renormalizable linear couplings to Standard Model fields and therefore be singly produced at colliders. We show that this classification exhausts the list of heavy scalar particles that contribute at the tree level to the Standard Model effective Lagrangian to dimension six. We compute this effective Lagrangian for a general scenario with an arbitrary number of new scalar particles and obtain flavor-preserving constraints on their couplings and masses. This completes the tree-level matching of the coefficients of dimension five and six operators in the effective Lagrangian to arbitrary extensions of the Standard Model.

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arXiv2011

Z' Bosons and Friends

The invariance of extensions of the Standard Model under the full SU(3)XSU(2)XU(1) gauge group can be used to classify general vector bosons and to write their interactions in a model-independent fashion. This description is useful for both direct and indirect searches. We comment on electroweak precision limits and show some simple applications to Higgs and top physics.

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arXiv2009

Unparticle signals with a few particles

We use Pade approximants to systematically approximate scalar unparticle propagators and their associated phase factors by a finite number of ordinary particles. This is possible for conformal dimensions 1 2 if we add local terms. A small number of particles can, in some cases, mimic unparticle signals. We also discuss how the approximants capture basic unparticle properties.

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arXiv2009

Electroweak Precision Observables and the Unhiggs

We compute one-loop corrections to the S and T parameters in the Unhiggs scenario. In that scenario, the Standard Model Higgs is replaced by a non-local object, called the Unhiggs, whose spectral function displays a continuum above the mass gap. The Unhiggs propagator has effectively the same UV properties as the Standard Model Higgs propagator, which implies that loop corrections to the electroweak precision observables are finite and calculable. We show that the Unhiggs is consistent with electroweak precision tests when its mass gap is at the weak scale; in fact, it then mimics a light SM Higgs boson. We also argue that the Unhiggs, while being perfectly visible to electroweak precision observables, is invisible to detection at LEP.

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arXiv2008

Holographic Unhiggs

We propose an extra-dimensional approach to the unparticle Higgs (Unhiggs). The non-local 4D Unhiggs action is derived as the boundary effective action of a local 5D theory. We review the mechanism to generate unparticle spectra in the context of warped soft-wall models. Gauge invariance can be simply implemented and unitarity of the longitudinal WW scattering amplitude is particularly transparent. Furthermore, the 5D approach uncovers a broader spectrum of phenomenological possibilities. The Unhiggs is accompanied by another continuum formed by Kaluza-Klein excitations of the Standard Model gauge fields which, in some cases, may take over the leading role in unitarizing WW scattering.

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arXiv2008

Electroweak Breaking on a Soft Wall

We extend the 5D gauge-higgs scenario to the soft-wall framework where the IR brane is replaced by a smoothly decaying warp factor. The electroweak symmetry of the Standard Model is embedded in a larger symmetry group whose gauge bosons propagate in the bulk of a warped fifth dimension. This gauge symmetry is partly broken by UV boundary conditions and by a condensate of a bulk scalar field. The Higgs boson lives partly in the 5th component of the gauge field, and partly in the the bulk scalar. The Higgs potential is not UV sensitive if the condensate vanishes fast enough in the UV region. The soft-wall realization opens new possibilities for the spectrum and the couplings of the Kaluza-Klein resonances. We study two particular soft-wall backgrounds: one with resonances whose masses follow the linear Regge trajectory, and another with a continuum above a mass gap. We find that constraints on the Kaluza-Klein scale from electroweak precision tests are less severe than in analogous models with the IR brane. For the linear spectrum the typical constraint on the lightest resonance mass is 2 TeV, while the continuum is allowed to start below 1 TeV.

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arXiv2006

Holography, Pade Approximants and Deconstruction

We investigate the relation between holographic calculations in 5D and the Migdal approach to correlation functions in large N theories. The latter employs Pade approximation to extrapolate short distance correlation functions to large distances. We make the Migdal/5D relation more precise by quantifying the correspondence between Pade approximation and the background and boundary conditions in 5D. We also establish a connection between the Migdal approach and the models of deconstructed dimensions.

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arXiv2006

Tools for Deconstructing Gauge Theories in AdS5

We employ analytical methods to study deconstruction of 5D gauge theories in the AdS5 background. We demonstrate that using the so-called q-Bessel functions allows a quantitative analysis of the deconstructed setup. Our study clarifies the relation of deconstruction with 5D warped theories.

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arXiv2006

Effective description of brane terms in extra dimensions

We study how theories defined in (extra-dimensional) spaces with localized defects can be described perturbatively by effective field theories in which the width of the defects vanishes. These effective theories must incorporate a ``classical'' renormalization, and we propose a renormalization prescription a la dimensional regularization for codimension 1, which can be easily used in phenomenological applications. As a check of the validity of this setting, we compare some general predictions of the renormalized effective theory with those obtained in a particular ultraviolet completion based on deconstruction.

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arXiv2004

Discrete regularisation of localised kinetic terms

We investigate the behaviour of 5d models with general brane kinetic terms by discretising the extra dimension. We show that in the continuum limit the Kaluza-Klein masses and wave functions are in general nonanalytic in the coefficients of brane terms.

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arXiv2004

Fermion Generations, Masses and Mixing Angles from Extra Dimensions

We discuss a toy model in six dimensions that predicts two fermion generations, natural mass hierarchy and intergenerational mixing. Matter is described by vector-like six dimensional fermions, one per each irreducible standard model representation. Two fermion generations arise from the compactification mechanism, through orbifold projection. They are localized in different regions of the compact space by a six dimensional mass term. Flavour symmetry is broken via Yukawa couplings, with a Higgs vacuum expectation value not constant in the extra space. A hierarchical spectrum is obtained from order one dimensionless parameters of the six dimensional theory. The Cabibbo angle arises from the soft breaking of six dimensional parity symmetry. We also briefly discuss how the present model could be extended to cover the realistic case.

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arXiv2001

Randall-Sundrum models and the regularized AdS/CFT correspondence

It has been proposed that Randall-Sundrum models can be holographically described by a regularized (broken) conformal field theory. We analyze the foundations of this duality using a regularized version of the AdS/CFT correspondence. We compare two- and three-point correlation functions and find the same behaviour in both descriptions. In particular, we show that the regularization of the deformed CFT generates kinetic terms for the sources, which hence can be naturally treated as dynamical fields. We also discuss the counterterms required for two- and three-point correlators in the renormalized AdS/CFT correspondence.

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arXiv2001

Physical (ir)relevance of ambiguities to Lorentz and CPT violation in QED

We discuss the regularization and renormalization of QED with Lorentz and CPT violation, and argue that the coefficient of the Chern-Simons term is an independent parameter not determined by gauge invariance. We also study these issues in a model with spontaneous breaking of Lorentz and CPT symmetries and find an explicit relation with the ABJ anomaly. This explains the observed convergence of the induced Chern-Simons term.

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