Antonio Dobado

• Doctor of Philosophy
• Complutense University of Madrid

In the context of $f(R)$ gravity, as well as other extended theories of gravity, the correct counting of globally well-defined dynamical modes has recently drawn a vivid interest. In this communication we present a consistent approach shedding light on such issues for both so-called degenerate and non-degenerate $f(R)$ models embedded in maximally-...

Constant-curvature solutions lie at the very core of gravitational physics, with Schwarzschild and (anti-)de Sitter being two of the most paradigmatic examples. Although such a kind of solutions are very well-known in general relativity, that is not the case for theories of gravity beyond the Einsteinian paradigm. In this article, we provide a syst...

We study the one-loop corrections to W+W− elastic scattering within the framework of effective theories. Rescattering via intermediate electroweak would-be-Goldstone bosons dominate at high energies, as the corresponding loop diagrams with these intermediate bosons scale like O(s2/v4) in the chiral effective counting. In the present article, we foc...

Some effective field theories exhibit dynamical resonances that, when properly included, mitigate their bad behavior at high energies. Unitarization of the partial wave amplitudes is the preferred method to unveil such resonances. Interpreting the Einstein-Hilbert theory in the spirit of effective Lagrangians, we implement the inverse amplitude met...

In this work we interpret the Einstein-Hilbert (EH) Lagrangian of gravitation as the first term of a low-energy effective theory similar to those considered in the chiral Lagrangian approach to low-energy hadron physics or the electroweak chiral Lagragians describing the symmetry breaking sector of the Standard Model (SM). Starting from the one-loo...

We present the contributions to the imaginary part of the $W^+W^-$ elastic scattering from top and bottom quark one-loop diagrams. The computation is performed within the context of HEFT, where we compare them with the boson-loop corrections. We argue that the often neglected (top and bottom) fermion contributions may in fact be relevant.

In this work we interpret the Einstein-Hilbert (EH) Lagrangian of gravitation as the first term of a low-energy effective theory similar to those considered in the chiral Lagrangian approach to low-energy hadron physics or the electroweak chiral Lagragians describing the symmetry breaking sector of the Standard Model (SM). Starting from the one-loo...

Some effective field theories exhibit dynamical resonances that, when properly included, mitigate their bad behaviour at high energies. Unitarization of the partial wave amplitudes is the preferred method to unveil such resonances. Interpreting the Einstein-Hilbert theory in the spirit of effective Lagrangians, we implement the Inverse Amplitude Me...

We study the one-loop corrections to Vector Boson Scattering (in particular $W^+W^-$ elastic scattering) within the framework of effective theories. Re-scattering via intermediate electroweak would-be-Goldstone bosons dominate at high energies, as the corresponding loop diagrams with these intermediate bosons scale like $\mathcal{O}(s^2/v^4)$ in th...

Gravitational collapse is still poorly understood in the context of f(R) theories of gravity, since the Oppenheimer-Snyder model is incompatible with their junction conditions. In this work, we will present a systematic approach to the problem. Starting with a thorough analysis of how the Oppenheimer-Snyder construction should be generalized to fit...

Gravitational collapse is still poorly understood in the context of $f(R)$ theories of gravity, since the Oppenheimer-Snyder model is incompatible with their junction conditions. In this work, we will present a systematic approach to the problem. Starting with a thorough analysis of how the Oppenheimer-Snyder construction should be generalised to f...

We test the assumption that fermion-loop corrections to high energy W⁺W⁻ scattering are negligible when compared to the boson-loop ones. Indeed, we find that, if the couplings of the interactions deviate from their Standard Model values, fermion-loop corrections can in fact become as important or even greater than boson-loop corrections for some pa...

We test the assumption that fermion-loop corrections to high energy $W^+W^-$ scattering are negligible when compared to the boson-loop ones. Indeed, we find that, if the couplings of the interactions deviate from their Standard Model values, fermion-loop corrections can in fact become as important or even greater than boson-loop corrections for som...

We calculate fermion-loop corrections to high energy $W^+W^-$ scattering in the context of a Strongly Interacting Electroweak Symmetry Breaking Sector (EWSBS) using Higgs Effective Field Theory(HEFT). We test the assumption that these corrections are negligible when compared to the boson-loop ones, as it is commonly taken for granted in the literat...

This article presents a number of technical tools and results that may be instrumental to discern the nature of the Higgs particle. In scenarios where an additional strongly interacting sector is present in the electroweak theory, resulting in a composite Higgs and longitudinal components of the massive gauge bosons, unitarity, analyticity and rela...

This article presents a number of technical tools and results that may be instrumental to discern the nature of the Higgs particle. In scenarios where an additional strongly interacting sector is present in the electroweak theory resulting in a composite Higgs and longitudinal components of the massive gauge bosons, unitarity, analyticity and relat...

Higgs Effective Field Theory (HEFT) is deployed to study elastic vector-boson scattering at the high LHC energies. The interaction is strong over most of the parameter space, with the minimal Standard Model being a remarkable exception. One-loop HEFT complemented with dispersion relations and the Equivalence Theorem leads to two different unitariza...

In this work we study the chiral phase transition as observed by an accelerating observer taking into account the Unruh effect. We use chiral perturbation theory at leading order and the large N limit (N being the number of pions) as an effective description of low-energy QCD, and the thermalization theorem to compute the relevant partition functio...

A bstract We estimate production cross sections for 2-body resonances of the Electroweak Symmetry Breaking sector (in W L W L and Z L Z L rescattering) from γγ scattering. We employ unitarized Higgs Effective Field Theory amplitudes previously computed coupling the two photon channel to the EWSBS. We work in the Effective Photon Approximation and e...

Higgs Effective Field Theory can be used to study vector-boson elastic scattering at the high energies relevant for the LHC. For most of the parameter space, the scattering is strongly interacting, with the minimal Standard Model being a remarkable exception. From its one-loop treatment complemented with dispersion relations and the Equivalence The...

A bstract We examine the production of Wh and Zh pairs at the LHC in the context of a Strongly Interacting Symmetry Breaking Sector of the Standard Model. Our description is based on a non-linear Higgs Effective Theory, including only the Standard Model particles. We focus on its scalar sector (Higgs boson h and electroweak Goldstones associated to...

We examine the production of Wh and Zh pairs at the LHC in the context of a Strongly Interacting Symmetry Breaking Sector of the Standard Model. Our description is based on a non-linear Higgs Effective Theory, including only the Standard Model particles. We focus on its scalar sector (Higgs boson h and electroweak Goldstones associated to $W_L^\pm$...

We estimate production cross sections for 2-body resonances of the Electroweak Symmetry Breaking sector (in W_L W_L, Z_L Z_L and hh rescattering) through intermediate photon-photon scattering. We employ unitarized Higgs Effective Theory amplitudes previously computed coupling the two photon channel to the EWSBS. We work in the Effective Photon Appr...

We report computations of the production cross-section of longitudinal electroweak and Higgs boson pairs within Effective Field Theory for the Electroweak sector (including the Higgs). We have recently reported theoretical studies of gauge boson-gauge boson and Higgs-Higgs resonance production with various quantum numbers. We are now focusing on ga...

In this work we consider the spontaneous symmetry breaking of the electroweak $SU(2)_L\times U(1)_Y$ gauge group into $U(1)_{em}$ taken place in the Standard Model of particle physics as seen from the point of view of an accelerating observer. According to the Unruh effect that observer detects the Minkowski vacuum as a thermal bath at a temperatur...

Due to the gap between the known 100 GeV scale and new physics if any, it is natural to employ an effective one-loop Lagrangian (HEFT) for the particles of the Electroweak Symmetry Breaking Sector (W_L, Z_L and h). To describe any new particles and resonances that may be found at the LHC we employ its unitarized amplitudes, valid even in the presen...

We define and calculate helicity partial-wave amplitudes for processes linking the Electroweak Symmetry Breaking Sector (EWSBS) to $\gamma\gamma$, employing (to NLO) the Higgs-EFT (HEFT) extension of the Standard Model and the Equivalence Theorem, while neglecting all particle masses. The resulting amplitudes can be useful in the energy regime ($50...

We define and calculate helicity partial-wave amplitudes for processes linking the Electroweak Symmetry Breaking Sector (EWSBS) to $\gamma\gamma$, employing (to NLO) the Higgs-EFT (HEFT) extension of the Standard Model and the Equivalence Theorem, while neglecting all particle masses. The resulting amplitudes can be useful in the energy regime ($50...

We point out that in the early universe, for temperatures in the approximate interval 150–80 MeV (after the quark–gluon plasma), pions carried a large share of the entropy and supported the largest inhomogeneities. Its thermal conductivity (previously calculated) allows the characterization of entropy production due to equilibration (damping) of th...

By using a Non-linear Electroweak Chiral Lagrangian, including the Higgs, coupled to heavy quarks, and the Equivalence Theorem, we compute (in the regime $M_t^2/v^2\ll\sqrt{s}M_t/v^2\ll s/v^2$) the one-loop amplitudes $W^+W^-\to t\bar t$, $ZZ\to t\bar t$ and $hh\to t\bar t$ (to NLO in the effective theory). We calculate the scalar partial-wave heli...

By using a Non-linear Electroweak Chiral Lagrangian, including the Higgs, coupled to heavy quarks, and the Equivalence Theorem, we compute (in the regime $M_t^2/v^2\ll\sqrt{s}M_t/v^2\ll s/v^2$) the one-loop amplitudes $W^+W^-\to t\bar t$, $ZZ\to t\bar t$ and $hh\to t\bar t$ (to NLO in the effective theory). We calculate the scalar partial-wave heli...

Recently, a new boson h has been discovered at the LHC which, so far, is compatible with the properties of the SM Higgs. However, the SM is not the most general low-energy dynamics for the minimal electroweak symmetry breaking sector with three Goldstone bosons and one light scalar. By using non-linear effective Lagrangian for these four particles...

The apparent finding of a 125 GeV light Higgs boson would close the minimal Standard Model (SM), that is weakly interacting. This is an exceptional feature not generally true if new physics exists beyond the mass gap found at the LHC up to 700 GeV. Any such new physics would induce departures from the SM in the low-energy dynamics for the minimal e...

Tantalizing LHC hints suggest that resonances of the Electroweak Symmetry Breaking Sector might exist at the TeV scale. We recall a few key meson-meson resonances in the GeV region that could have high-energy analogues which we compare, as well as the corresponding unitarized effective theories describing them. While detailed dynamics may be differ...

If new resonances of the electroweak symmetry breaking sector (longitudinal-gauge and Higgs) bosons are found in the 1-3 TeV region, the right tool to assess their properties and confront experimental data in a largely model-independent yet simple manner is Unitarized Effective Theory. Its ingredients are: 1) custodial symmetry and the Equivalence...

The LHC is now exploring the 1-3 TeV scale where resonances of the Electroweak Symmetry Breaking Sector might exist. If so, Unitarized Effective Theory can be used to describe the data with all the constraints of unitarity, causality and global-symmetry breaking, and to find the resonance positions in the complex s-plane. From any resonances found,...

We are exploring a generic strongly-interacting Electroweak Symmetry Breaking Sector (EWSBS) with the low-energy effectie field theory for the four experimentally known particles ($W_L^\pm$, $Z_L$, $h$) and its dispersion-relation based unitary extension. In this contribution we provide simple estimates for the production cross section of pairs of...

If the Electroweak Symmetry Breaking Sector turns out to be strongly interacting, the actively investigated effective theory for longitudinal gauge bosons plus Higgs can be efficiently extended to cover the regime of saturation of unitarity (where the perturbative expansion breaks down). This is achieved by dispersion relations, whose subtraction c...

Recently, a new boson h has been discovered at the LHC which, so far, is compatible with the properties of the SM Higgs. However, the SM is not the most general low-energy dynamics for the minimal electroweak symmetry breaking sector with three Goldstone bosons and one light scalar. By using non-linear effective Lagrangian for these four particles...

We propose and theoretically study a possible new resonance caused by strong coupling between the Higgs-Higgs and the W_L W_L (Z_L Z_L) scattering channels, without regard to the intensity of the elastic interaction in either channel at low energy (that could be weak as in the Standard Model). We expose this channel-coupling resonance from unitarit...

The apparent finding of a 125-GeV light Higgs boson closes unitarity of the minimal Standard Model (SM), that is weakly interacting: this is an exceptional feature not generally true if new physics exists beyond the mass gap found at the LHC up to 700 GeV. Such new physics induces departures of the low-energy dynamics for the minimal electroweak sy...

The claimed finding of a light Higgs boson makes the minimal Standard Model unitary. Yet, we recall that the general low-energy dynamics for the minimal electroweak symmetry breaking sector with three Goldstone bosons and one light scalar is not so. We construct the effective Lagrangian for these four particles and their scattering amplitudes, that...

By including the recently discovered Higgs-like scalar in the Electroweak Chiral Lagrangian, and using the Equivalence Theorem, we carry out the complete one-loop computation of the elastic scattering amplitude for the longitudinal components of the gauge bosons at high energy. We also compute phi phi -> phi phi and the inelastic process VV -> phi...

We study the possibility of testing some generic properties of brane world scenarios at the LHC. In particular, we pay attention to Kaluza-Klein graviton and branon production. Both signals can be dominant depending on the value of the brane tension. We analyze the differences between these two signatures. Finally, we use recent data in the single...

We explore the viscosities of a photon gas by means of the Euler-Heisenberg effective theory and quantum electrodynamics at zero electron chemical potential. We find parametric estimates that show a very large shear viscosity and an extremely small bulk viscosity (reflecting the very weak coupling simultaneously with a very approximate dilatation i...

We study the possibility of testing some generic properties of Brane-World scenarios at the LHC. In particular, we pay attention to KK-graviton and branon production. Both signals can be dominant depending on the value of the brane tension. We analyze the differences between these two signatures. Finally, we use recent data in the single photon cha...

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In this work we deal with the critical behavior of the bulk viscosity in the linear sigma model (LSM) as an example of a system which can be treated by using different techniques. Starting from the Boltzmann-Uehling-Uhlenbeck equation we compute the bulk viscosity over entropy density of the LSM in the large-N limit. We search for a possible maximu...

In General Relativity there is a maximum mass allowed for neutron stars that, if exceeded, entails their collapse into a black hole. Its precise value depends on details of the nuclear matter equation of state about which we are much more certain thanks to recent progress in low-energy effective theories. The discovery of a two-solar mass neutron s...

We calculate the bulk viscosity of a pion gas at low energies within the kinetic theory approach and show the importance of dealing properly with the zero modes of this transport coefficient.

We study the bulk viscosity of a pion gas in unitarized Chiral Perturbation Theory at low and moderate temperatures, below any phase transition to a quark-gluon plasma phase. We argue that inelastic processes are irrelevant and exponentially suppressed at low temperatures. Since the system falls out of chemical equilibrium upon expansion,a pion che...

We show how the measurement of appropriately constructed particle-energy/momentum correlations allows access to the bulk viscosity of strongly interacting hadron matter in heavy ion collisions. This measurement can be performed by the LHC and RHIC experiments in events with high-particle multiplicity, following up on existing estimates of the shear...

We introduce the concept of viscosity (both shear and bulk) in the context of hadron physics and in particular the meson gas, highlighting the current theoretical efforts to connect possible measurements of the viscosities to underlying physics such as a phase transition or the trace anomaly.

Probably the most enticing observation in theoretical physics during the last decade was the discovery of the great amount of consequences obtained from the AdS/CFT conjecture put forward by Maldacena. In this work we review how this correspondence can be used to address hydrodynamic properties such as the viscosity of some strongly interacting sys...

We reexamine the possibility of employing the viscosity over entropy density ratio as a diagnostic tool to identify a phase transition in hadron physics to the strongly coupled quark-gluon plasma and other circumstances where direct measurement of the order parameter or the free energy may be difficult. It has been conjectured that the minimum of e...

In this work we compute the radiative corrections to the Higgs mass and the Higgs quartic couplings coming from the Higgs sector itself and the scalar fields $\phi$ in the Littlest Higgs (LH) model. The restrictions that the new contributions set on the parameter space of the models are also discussed. Finally this work, together with our three pre...

The viscosity over entropy density ratio, or KSS number, can help isolate the critical point in the hadron phase‐diagram in Relativistic Heavy Ion Collisions. We argue that this quantity does have a minimum at a phase transition or crossover. Although indications from conventional non‐relativistic gases point out to even a divergence in η/s when...

We present a calculation of η/s for the meson gas (zero baryon number), with the viscosity computed within unitarized next-to-leading-order chiral perturbation theory, and confirm the observation that η/s decreases towards the possible phase transition to a quark-gluon plasma/liquid. The value is somewhat higher than previously estimated in leading...

In this work we briefly review the Kovtun‐Son‐Starinet (KSS) computation of the ratio η/s for quantum field theories with gravitational dual and the related conjecture that it is bound from below by 1/4π. We discuss the validity of the bound and the nature of its possible violations, its relevance for RHIC, its connection with phase transitio...

We present a calculation of eta/s for the meson gas (zero baryon number) within unitarized NLO chiral perturbation theory and confirm the observation that eta/s decreases towards the possible phase transition to a quark-gluon plasma/liquid. The value is however somewhat higher than previously estimated in LO chiPT. We then study the behavior of the...

In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the dark energy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require and urgent solution for the sake of the internal consistency of theoretical phys...

We compute the relevant parameters of the combined Higgs and \phi scalar effective potential in the Littlest Higgs (LH) model. These parameters are obtained as the sum of two kind of contributions. The first one is the one-loop radiative corrections coming from fermions and gauge bosons. The second one is obtained at the tree level from the higher...

We compute the relevant parameters of the combined Higgs and \phi scalar effective potential in the Littlest Higgs (LH) model. These parameters are obtained as the sum of two kind of contributions. The first one is the one-loop radiative corrections coming from fermions and gauge bosons. The second one is obtained at the tree level from the higher...

It has been suggested that our universe could be a 3-dimensional brane where the SM fields live embedded in a D-dimensional space-time. In flexible raneworlds, in addition to the SM fields, new degrees of freedom appear on the brane associated to brane fluctuations. These new fields, known as branons, are standard WIMPs (Weakly Interacting Massive...

12 pages, 6 figures.-- PACS nrs.: 95.35.+d; 11.10.Kk; 11.25.-w.-- ISI Article Identifier: 000246076900042.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0612131 In this work we compute the contributions to the Higgs effective potential coming from the fermion and gauge boson sectors at the one-loop level in the context of the SU(5)/SO...

We evaluate the heat conductivity of a dilute pion gas employing the Uehling-Uehlenbeck equation and experimental phase-shifts parameterized by means of the SU(2) Inverse Amplitude Method. Our results are consistent with previous evaluations. For comparison we also give results for an (unphysical) hard sphere gas.

The QNP series of international conferences on Quarks and Nuclear Physics is by now a well established and highly respected forum where the most recent developments in the field are discussed and communicated. QNP 2006 is the forth edition of this biennial meeting. Selected and refereed original contributions of QNP 2006 have been published in The...

8 pages, 3 figures.-- ISI Article Identifier: 000245853100015.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0606031 Printed version published Apr 2007. In SU(5)/SO(5) little Higgs models radiative corrections give rise to SU(2)(L)xU(1)(Y) symmetry breaking. In this work we start a program for a detailed determination of the relevant...

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We summarize the main features of several dark matter candidates in extra-dimensional theories. In particular, we review Kaluza-Klein (KK) gravitons in universal extra dimensions and branons in brane-world models. KK gravitons are superWIMP (superweakly-interacting massive particle) dark matter, and branons are WIMP (weakly-interacting massive part...

In this work we review at an elementary level the origin, main ideas and present status of the so called holographic principle. This principle, even in the absence of a precise formulation, is seen by many people as a major clue for the understanding of the relationship betweeen quantum mechanics and general relativity. The topics considered here i...

We report a calculation of the shear viscosity in a relativistic multicomponent meson gas as a function of temperature and chemical potentials. We approximately solve the Uehling-Uhlenbeck transport equation of kinetic theory, appropriate for a boson gas, with relativistic kinematics. Since at low temperatures the gas can be taken as mostly compose...

We compute the mean free path and shear viscosity in the color-flavor locked (CFL) phase of dense quark matter at low temperature T, when the contributions of mesons, quarks and gluons to the transport coefficients are Boltzmann suppressed. CFL quark matter displays superfluid properties, and transport phenomena in such cold regime are dominated by...

We report a calculation of the shear viscosity in a relativistic multicomponent meson gas as a function of temperature and chemical potentials. We approximately solve the Uehling-Uhlenbeck transport equation of kinetic theory, appropriate for a boson gas, with relativistic kinematics. Since at low temperatures the gas can be taken as mostly compose...

We briefly report a calculation of the viscosity of a pion gas at finite temperature and chemical potential using three different models for the pion-pion interaction. The results for the Inverse Amplitude Method interpolation yield a viscosity of order (m_pi^3) up to temperatures of order m_pi. The calculation is performed within the kinetic theor...

We show that the effects of heavy Higgs particles and heavy top-squarks in the one-loop self-couplings of the lightest CP-even MSSM Higgs boson decouple from the low energy theory when the self-couplings are expressed in terms of the Higgs boson mass M_h0. Our conclusion is that the h^0 self-interactions become very close to those of the SM Higgs b...

By using Chiral Perturbation Theory and the Uehling-Uhlenbeck equation we compute the viscosity of a pion gas, in the low temperature and low density regime, in terms of the temperature, and the pion fugacity. The viscosity turns out to be proportional to the squared root of the temperature over the pion mass. Next to leading corrections are propor...

In this paper we study the Yukawa Higgs-quark-quark interactions that are generated from radiative corrections of squarks and gluinos, in the minimal supersymmetric standard model. We compute the corrections to the effective action for Higgs and quark fields that are produced by explicit integration in the path integral formalism of all the squarks...

In this work we calculate the low-energy effective action for gravity with torsion, obtained after the integration of scalar and fermionic matter fields, using the local momentum representation based on the Riemann normal coordinates expansion. By considering this expansion around different spacetime points, we also compute the non-local terms toge...

Torsion appears in a natural way in modern formulations of the gravitational theories. In this work we study several aspects of the interplay between the Standard Model and a classical gravitational background with torsion. In particular we consider the problem of the gauge and gravitational anomalies, $B$ and $L$ anomalies, the effective action fo...

In this paper we show how the nonlocal effective action for gravity, obtained after integrating out the matter fields, can be used to compute particle production and spectra for different space-time metrics. Applying this technique to several examples, we find that the perturbative calculation of the effective action up to second order in curvature...

In this note we provide a simple explanation of the recent finding of anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston (astro-ph/9704196). We consider, as a possible origin of such effect, the effective coupling between EM fields and some tiny background torsion field. The coupling is obtained after integrating out char...

In the presence of a curved space-time with torsion, the divergence of the leptonic current gets new contributions from the curvature and the torsion in addition to those coming from the electroweak fields. However it is possible to define a new lepton current which is gauge and local Lorentz invariant whose divergence gets no contribution from the...

In this chapter, we deal with the standard model (SM) of elementary particles interacting with classical gravity. Within this framework, we study the cancellation of anomalies in gauge and Lorentz currents as well as lepton and baryon number violation. We also consider the effect of the matter fields on gravitation. Finally, the pure gravitational...

In previous chapters, we have studied the formal development of the effective Lagrangian formalism. In Chap. 3 we have seen how to obtain the non-linear sigma model (NLSM) Lagrangian. This is the lowest order term in the derivative expansion that describes the dynamics of the Nambu-Goldstone Bosons (NGB), which are the low-energy excitations of the...

In this chapter we try to give a motivation for the study of effective La-grangians, as well as a brief introduction to their main features. We also discuss the important notion of decoupling and analyze the cases in which this property holds.

Symmetries play an important role in the determination of the structure of the different terms appearing in an effective Lagrangian. For this reason we briefly review in this chapter the basic notions related with global symmetries in quantum field theories (QFT). Starting from the Noether theorem for classical systems we derive the Ward identities...

In this chapter we are going to review the mass problem in the standard model (SM) and how it is solved by means of an spontaneous symmetry breaking. This mechanism also admits a phenomenological description in terms of an electroweak effective Lagrangian, that is built based on just a few firmly established experimental facts. We will see that its...