Riccardo Rattazzi - Academia.edu (original) (raw)

Papers by Riccardo Rattazzi

Nuclear Physics B, 2006

We stress that the lack of direct evidence for supersymmetry forces the soft mass parameters to l... more We stress that the lack of direct evidence for supersymmetry forces the soft mass parameters to lie very close to the critical line separating the broken and unbroken phases of the electroweak gauge symmetry. We argue that the level of criticality, or fine-tuning, that is needed to escape the present collider bounds can be quantitatively accounted for by assuming that

We review CP violation in various extensions of the electroweak sector of the Standard Model. A p... more We review CP violation in various extensions of the electroweak sector of the Standard Model. A particular emphasis is put on supersymmetric models. We describe the two CP problems of supersymmetry, concerning dNd_NdN and epsilonK\epsilon_KepsilonK. We critically review the various mechanisms that have been suggested to solve these problems: exact universality, approximate CP symmetry, alignment, approximate universality and heavy squarks.

Nuclear Physics B, 2001

We investigate the properties of scalar fields arising from gravity propagating in extra dimensio... more We investigate the properties of scalar fields arising from gravity propagating in extra dimensions. In the scenario of large extra dimensions, proposed by Arkani-Hamed, Dimopoulos and Dvali, graviscalar Kaluza-Klein excitations are less important than the spin-2 counterparts in most processes. However, there are important exceptions. The Higgs boson can mix to these particles by coupling to the Ricci scalar. Because of the large number of states involved, this mixing leads, in practice, to a sizeable invisible width for the Higgs. In the Randall-Sundrum scenario, the only graviscalar is the radion. It can be produced copiously at hadron colliders by virtue of its enhanced coupling to two gluons through the trace anomaly of QCD. We study both the production and decay of the radion, and compare it to the Standard Model Higgs boson. Furthermore, we find that radion detectability depends crucially on the curvature-Higgs boson mixing parameter.

Journal of High Energy Physics, 2003

The model of Dvali, Gabadadze, and Porrati (DGP) gives a simple geometrical setup in which gravit... more The model of Dvali, Gabadadze, and Porrati (DGP) gives a simple geometrical setup in which gravity becomes 5-dimensional at distances larger than a length scale λ DGP . We show that this theory has strong interactions at a length scale λ 3 ∼ (λ 2 DGP /M P ) 1/3 . If λ DGP is of order the Hubble length, then the theory loses predictivity at distances shorter than λ 3 ∼ 1000 km. The strong interaction can be viewed as arising from a longitudinal 'eaten Goldstone' mode that gets a small kinetic term only from mixing with transverse graviton polarizations, analogous to the case of massive gravity. We also present a negativeenergy classical solution, which can be avoided by cutting off the theory at the same scale scale λ 3 . Finally, we examine the dynamics of the longitudinal Goldstone mode when the background geometry is curved.

Journal of High Energy Physics, 2014

The local Callan-Symanzik equation describes the response of a quantum field theory to local scal... more The local Callan-Symanzik equation describes the response of a quantum field theory to local scale transformations in the presence of background sources. The consistency conditions associated with this anomalous equation imply non-trivial relations among the β-function, the anomalous dimensions of composite operators and the short distance singularities of correlators. In this paper we discuss various aspects of the local Callan-Symanzik equation and present new results regarding the structure of its anomaly. We then use the equation to systematically write the n-point correlators involving the trace of the energy-momentum tensor. We use the latter result to give a fully detailed proof that the UV and IR asymptotics in a neighbourhood of a 4D CFT must also correspond to CFTs. We also clarify the relation between the matrix entering the gradient flow formula for the β-function and a manifestly positive metric in coupling space associated with matrix elements of the trace of the energy momentum tensor.

We derive model-independent lower bounds on the stress tensor central charge C_T in terms of the ... more We derive model-independent lower bounds on the stress tensor central charge C_T in terms of the operator content of a 4-dimensional Conformal Field Theory. More precisely, C_T is bounded from below by a universal function of the dimensions of the lowest and second-lowest scalars present in the CFT. The method uses the crossing symmetry constraint of the 4-point function, analyzed

Physical Review D, 2009

In the DGP model, the "self-accelerating" solution is plagued by a ghost instability, which makes... more In the DGP model, the "self-accelerating" solution is plagued by a ghost instability, which makes the solution untenable. This fact as well as all interesting departures from GR are fully captured by a four-dimensional effective Lagrangian, valid at distances smaller than the present Hubble scale. The 4D effective theory involves a relativistic scalar π, universally coupled to matter and with peculiar derivative self-interactions. In this paper, we study the connection between self-acceleration and the presence of ghosts for a quite generic class of theories that modify gravity in the infrared. These theories are defined as those that at distances shorter than cosmological, reduce to a certain generalization of the DGP 4D effective theory. We argue that for infrared modifications of GR locally due to a universally coupled scalar, our generalization is the only one that allows for a robust implementation of the Vainshtein effect-the decoupling of the scalar from matter in gravitationally bound systems-necessary to recover agreement with solar system tests. Our generalization involves an internal "galilean" invariance, under which π's gradient shifts by a constant. This symmetry constrains the structure of the π Lagrangian so much so that in 4D there exist only five terms that can yield sizable non-linearities without introducing ghosts. We show that for such theories in fact there are "self-accelerating" deSitter solutions with no ghost-like instabilities. In the presence of compact sources, these solutions can support spherically symmetric, Vainshtein-like non-linear perturbations that are also stable against small fluctuations. We investigate a possible infrared completion of these theories at scales of order of the Hubble horizon, and larger. There are however some features of our theories, that may constitute a problem at the theoretical or phenomenological level: the presence of superluminal excitations; the extreme sub-luminality of other excitations, which makes the quasi-static approximation for certain solar-system observables unreliable due to Cherenkov emission; the very low strong-interaction scale for ππ scatterings.

Journal of High Energy Physics, 2006

We study whether a violation of the null energy condition necessarily implies the presence of ins... more We study whether a violation of the null energy condition necessarily implies the presence of instabilities. We prove that this is the case in a large class of situations, including isotropic solids and fluids relevant for cosmology. On the other hand we present several counter-examples of consistent effective field theories possessing a stable background where the null energy condition is violated. Two necessary features of these counter-examples are the lack of isotropy of the background and the presence of superluminal modes. We argue that many of the properties of massive gravity can be understood by associating it to a solid at the edge of violating the null energy condition. We briefly analyze the difficulties of mimickingḢ > 0 in scalar tensor theories of gravity.

Journal of High Energy Physics, 2004

We study the Dvali-Gabadadze-Porrati model by the method of the boundary effective action. The tr... more We study the Dvali-Gabadadze-Porrati model by the method of the boundary effective action. The truncation of this action to the bending mode π consistently describes physics in a wide range of regimes both at the classical and at the quantum level. The Vainshtein effect, which restores agreement with precise tests of general relativity, follows straightforwardly. We give a simple and general proof of stability, i.e. absence of ghosts in the fluctuations, valid for most of the relevant cases, like for instance the spherical source in asymptotically flat space. However we confirm that around certain interesting self-accelerating cosmological solutions there is a ghost. We consider the issue of quantum corrections. Around flat space π becomes strongly coupled below a macroscopic length of 1000 km, thus impairing the predictivity of the model. Indeed the tower of higher dimensional operators which is expected by a generic UV completion of the model limits predictivity at even larger length scales. We outline a non-generic but consistent choice of counterterms for which this disaster does not happen and for which the model remains calculable and successful in all the astrophysical situations of interest. By this choice, the extrinsic curvature K µν acts roughly like a dilaton field controlling the strength of the interaction and the cut-off scale at each space-time point. At the surface of Earth the cutoff is ∼ 1 cm but it is unlikely that the associated quantum effects be observable in table top experiments.

Physics Letters B, 1997

The reported anomaly in deep-inelastic scattering at HERA has revived interest in the phenomenolo... more The reported anomaly in deep-inelastic scattering at HERA has revived interest in the phenomenology of R-parity violation. From the theoretical point of view, the existence of R-violating interactions poses two considerable problems. The first one concerns the flavour structure of the interactions and the origin of an appropriate suppression of flavourchanging neutral-current processes and lepton-family transitions. The second one concerns the way of embedding R-violating interactions in a grand unified theory (GUT) without introducing unacceptable nucleon decay rates. We show that the second problem can be solved by a mechanism which is purely group theoretical and does not rely on details of the flavour theory. We construct explicit GUT models in which our mechanism can be realized.

Nuclear Physics B, 1998

We show that in theories in which supersymmetry breaking is communicated by renormalizable pertur... more We show that in theories in which supersymmetry breaking is communicated by renormalizable perturbative interactions, it is possible to extract the soft terms for the observable fields from wave-function renormalization. Therefore all the information about soft terms can be obtained from anomalous dimensions and β functions, with no need to further compute any Feynman diagram. This method greatly simplifies calculations which are rather involved if performed in terms of component fields. For illustrative purposes we reproduce known results of theories with gauge-mediated supersymmetry breaking. We then use our method to obtain new results of phenomenological importance. We calculate the next-to-leading correction to the Higgs mass parameters, the two-loop soft terms induced by messenger-matter superpotential couplings, and the soft terms generated by messengers belonging to vector supermultiplets.

We consider the canonical quantization of an ordinary fluid. The resulting longdistance effective... more We consider the canonical quantization of an ordinary fluid. The resulting longdistance effective field theory is derivatively coupled, and therefore strongly coupled in the UV. The system however exhibits a number of peculiarities, associated with the vortex degrees of freedom. On the one hand, these have formally a vanishing strongcoupling energy scale, thus suggesting that the effective theory's regime of validity is vanishingly narrow. On the other hand, we prove an analog of Coleman's theorem, whereby the semiclassical vacuum has no quantum counterpart, thus suggesting that the vortex premature strong-coupling phenomenon stems from a bad identification of the ground state and of the perturbative degrees of freedom. Finally, vortices break the usual connection between short distances and high energies, thus potentially impairing the unitarity of the effective theory.

Journal of High Energy Physics, 2010

The hierarchy problem and the electroweak data, together, provide a plausible motivation for cons... more The hierarchy problem and the electroweak data, together, provide a plausible motivation for considering a light Higgs emerging as a pseudo-Goldstone boson from a strongly-coupled sector. In that scenario, the rates for Higgs production and decay differ significantly from those in the Standard Model. However, one genuine strong coupling signature is the growth with energy of the scattering amplitudes among

Physics Letters B, 2004

In 5 dimensions the electroweak symmetry can be broken by boundary conditions, leading to a new t... more In 5 dimensions the electroweak symmetry can be broken by boundary conditions, leading to a new type of Higgsless theories. These could in principle improve on the 4D case by extending the perturbative domain to energies higher than 4πv and by allowing a better fit to the electroweak precision tests. Nevertheless, it is unlikely that both these improvements can be achieved, as we show by discussing these problems in an explicit model.

Journal of High Energy Physics - J HIGH ENERGY PHYS, 2011

We consider a generic composite Higgs model based on the coset SO(5) /SO(4) and study its phenome... more We consider a generic composite Higgs model based on the coset SO(5) /SO(4) and study its phenomenology beyond the leading low-energy effective lagrangian approximation. Our basic goal is to introduce in a controllable and simple way the lowest-lying, possibly narrow, resonances that may exist is such models. We do so by proposing a criterion that we call partial UV completion. We characterize the simplest cases, corresponding respectively to a scalar in either singlet or tensor representation of SO(4) and to vectors in the adjoint of SO(4). We study the impact of these resonances on the signals associated to high-energy vector boson scattering, pointing out for each resonance the characteristic patterns of depletion and enhancement with respect to the leading-order chiral lagrangian. En route we derive the O( p 4) general chiral lagrangian and discuss its peculiar accidental and approximate symmetries.

Journal of High Energy Physics, 1999

We give a self-contained discussion of recent progress in computing the nonperturbative effects o... more We give a self-contained discussion of recent progress in computing the nonperturbative effects of small non-holomorphic soft supersymmetry breaking, including a simple new derivation of these results based on an anomalyfree gauged U(1) R background. We apply these results to N = 1 theories with deformed moduli spaces and conformal fixed points. In an SU(2) theory with a deformed moduli space, we completely determine the vacuum expectation values and induced soft masses. We then consider the most general soft breaking of supersymmetry in N = 2 SU(2) super-Yang-Mills theory. An N = 2 superfield spurion analysis is used to give an elementary derivation of the relation between the modulus and the prepotential in the effective theory. This analysis also allows us to determine the nonperturbative effects of all soft terms except a non-holomorphic scalar mass, away from the monopole points. We then use an N = 1 spurion analysis to determine the effects of the most general soft breaking, and also analyze the monopole points. We show that naïve dimensional analysis works perfectly. Also, a soft mass for the scalar in this theory forces the theory into a free Coulomb phase. * Sloan Fellow.

Journal of High Energy Physics, 2002

We study through holography the compact Randall-Sundrum (RS) model at finite temperature. In the ... more We study through holography the compact Randall-Sundrum (RS) model at finite temperature. In the presence of radius stabilization, the system is described at low enough temperature by the RS solution. At high temperature it is described by the AdS-Schwarzschild solution with an event horizon replacing the TeV brane. We calculate the transition temperature T c between the two phases and we find it to be somewhat smaller than the TeV scale. Assuming that the Universe starts out at T T c and cools down by expansion, we study the rate of the transition to the RS phase. We find that the transition is very slow so that an inflationary phase at the weak scale begins. The subsequent evolution depends on the stabilization mechanism: in the simplest Goldberger-Wise case inflation goes on forever unless tight bounds are satisfied by the model parameters; in slightly lessminimal cases these bounds may be relaxed.

Journal of High Energy Physics, 1998

In models with dynamical supersymmetry breaking in the hidden sector, the gaugino masses in the o... more In models with dynamical supersymmetry breaking in the hidden sector, the gaugino masses in the observable sector have been believed to be extremely suppressed (below 1 keV), unless there is a gauge singlet in the hidden sector with specific couplings to the observable sector gauge multiplets. We point out that there is a pure supergravity contribution to gaugino masses at the quantum level arising from the superconformal anomaly. Our results are valid to all orders in perturbation theory and are related to the 'exact' beta functions for soft terms. There is also an anomaly contribution to the A terms proportional to the beta function of the corresponding Yukawa coupling. The gaugino masses are proportional to the corresponding gauge beta functions, and so do not satisfy the usual GUT relations.

Journal of High Energy Physics, 2000

We clarify some general issues in models where gravity is localized at intermediate distances. We... more We clarify some general issues in models where gravity is localized at intermediate distances. We introduce the radion mode, which is usually neglected, and we point out that its role in the model is crucial. We show that the brane bending effects discussed in the literature can be obtained in a formalism where the physical origin is manifest. The model violates positivity of energy due to a negative tension brane, which induces a negative kinetic term for the radion. The very same effect that violates positivity is responsible for the recovery of conventional Einstein gravity at intermediate distances.

Journal of High Energy Physics, 2001

We discuss how to consistently perform effective Lagrangian computations in quantum gravity with ... more We discuss how to consistently perform effective Lagrangian computations in quantum gravity with branes in compact extra dimensions. A reparametrization invariant and infrared finite result is obtained in a non trivial way. It is crucial to properly account for brane fluctuations and to correctly identify physical observables. Our results correct some confusing claims in the literature. We discuss the implications of graviton loops on electroweak precision observables and on the muon g − 2 in models with large extra dimensions. We model the leading effects, not controlled by effective field theory, by introducing a hard momentum cut-off.