Search results for "theories"
showing 10 items of 302 documents
Lepton-flavour violation in hadronic tau decays and μ-τ conversion in nuclei
2021
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$--$\tau$ conversion in nuclei, with $\ell = e,\mu$. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments.
Global fit to b → cτν transitions
2019
Abstract We perform a general model-independent analysis of $$ b\to c\tau {\overline{\nu}}_{\tau } $$ b → cτ ν ¯ τ transitions, including measurements of ℛ D , ℛ D∗, their q 2 differential distributions, the recently measured longitudinal D* polarization $$ {F}_L^{D\ast } $$ F L D ∗ , and constraints from the $$ {B}_c\to \tau {\overline{\nu}}_{\tau } $$ B c → τ ν ¯ τ lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected $$ b\to c\tau {\overline{\nu}}_…
The Higgs sector of the munuSSM and collider physics
2011
Journal of High Energy Physics 2011.10 (2011): 020 reproduced by permission of Scuola Internazionale Superiore di Studi Avanzati (SISSA)
SU(5)-inspired double beta decay
2015
The short-range part of the neutrinoless double beta amplitude is generated via the exchange of exotic particles, such as charged scalars, leptoquarks and/or diquarks. In order to give a sizable contribution to the total decay rate, the masses of these exotics should be of the order of (at most) a few TeV. Here, we argue that these exotics could be the “light” (i.e., weak-scale) remnants of some B – L violating variants of SU(5). We show that unification of the standard model gauge couplings, consistent with proton decay limits, can be achieved in such a setup without the need to introduce supersymmetry. Since these nonminimal SU(5)-inspired models violate B – L, they generate Majorana neut…
Hidden charm molecules in finite volume
2013
In the present paper we address the interaction of pairs of charmed mesons with hidden charm in a finite box. We use the interaction from a recent model based on heavy-quark spin symmetry that predicts molecules of hidden charm in the infinite volume. The energy levels in the box are generated within this model, and from them some synthetic data are generated. These data are then employed to study the inverse problem of getting the energies of the bound states and phase shifts for D (D) over bar or D*(D) over bar*. Different strategies are investigated using the lowest two levels for different values of the box size, and the errors produced are studied. Starting from the upper level, fits t…
Higgs boson pair production in the D = 6 extension of the SM
2014
We derive the constraints that can be imposed on the dimension-6 effective theory extension of the Standard Model, using gluon fusion-initiated Higgs boson pair production at the LHC. We use a realistic analysis focussing on the hh→(bb¯¯)(τ+τ−) final state, including initial-state radiation and non-perturbative effects. We include the statistical uncertainties on the signal rates as well as conservative estimates of the theoretical uncertainties. We first consider a theory containing only modifications of the trilinear coupling, through a c6λ H6/v2 Lagrangian term, and then examine the full parameter space of the effective theory, incorporating current bounds obtained through single Higgs b…
Infra-Red Asymptotic Dynamics of Gauge Invariant Charged Fields: QED versus QCD
1999
The freedom one has in constructing locally gauge invariant charged fields in gauge theories is analyzed in full detail and exploited to construct, in QED, an electron field whose two-point function W(p), up to the fourth order in the coupling constant, is normalized with on-shell normalization conditions and is, nonetheless, infra-red finite; as a consequence the radiative corrections vanish on the mass shell $p^2=\mu^2$ and the free field singularity is dominant, although, in contrast to quantum field theories with mass gap, the eigenvalue $\mu^2$ of the mass operator is not isolated. The same construction, carried out for the quark in QCD, is not sufficient for cancellation of infra-red …
Non-perturbative renormalization of static-light four-fermion operators in quenched lattice QCD
2007
We perform a non-perturbative study of the scale-dependent renormalization factors of a multiplicatively renormalizable basis of $\Delta{B}=2$ parity-odd four-fermion operators in quenched lattice QCD. Heavy quarks are treated in the static approximation with various lattice discretizations of the static action. Light quarks are described by non-perturbatively ${\rm O}(a)$ improved Wilson-type fermions. The renormalization group running is computed for a family of Schroedinger functional (SF) schemes through finite volume techniques in the continuum limit. We compute non-perturbatively the relation between the renormalization group invariant operators and their counterparts renormalized in …
Hyperboloidal slicing approach to quasinormal mode expansions: The Reissner-Nordström case
2018
We study quasi-normal modes of black holes, with a focus on resonant (or quasi-normal mode) expansions, in a geometric frame based on the use of conformal compactifications together with hyperboloidal foliations of spacetime. Specifically, this work extends the previous study of Schwarzschild in this geometric approach to spherically symmetric asymptotically flat black hole spacetimes, in particular Reissner-Nordstr\"om. The discussion involves, first, the non-trivial technical developments needed to address the choice of appropriate hyperboloidal slices in the extended setting as well as the generalization of the algorithm determining the coefficients in the expansion of the solution in te…
General interpolation scheme for thermal fluctuations in superconductors
2006
We present a general interpolation theory for the phenomenological effects of thermal fluctuations in superconductors. Fluctuations are described by a simple gauge invariant extension of the gaussian effective potential for the Ginzburg-Landau static model. The approach is shown to be a genuine variational method, and to be stationary for infinitesimal gauge variations around the Landau gauge. Correlation and penetration lengths are shown to depart from the mean field behaviour in a more or less wide range of temperature below the critical regime, depending on the class of material considered. The method is quite general and yields a very good interpolation of the experimental data for very…