Higgs Physics

The cause of the screening of the weak interactions at long distances puzzled the high-energy community for more nearly half a century. With the discovery of the Higgs boson a new era started with direct experimental information on the physics behind the breaking of the electroweak symmetry. This breaking plays a fundamental role in our understanding of particle physics and sits at the high-energy frontier beyond which we expect new physics that supersedes the Standard Model. The Higgs boson (inclusive and differential) production and decay rates offer a new way to probe this frontier.Comment: 12 pages, contribution to the CERN in the Proceedings of the 2015 CERN-Latin-American School of High-Energy Physics, Ibarra, Ecuador, 4 - 17 March 201

T Self-Dual Transverse Space and Gravity Trapping

We advocate that the orbifold Z_2 symmetry of the gravity trapping model proposed by Randall and Sundrum can be seen, in appropriate coordinates, as a symmetry that exchanges the short distances with the large ones. Using diffeomorphism invariance, we construct extensions defined by patch glued together. A singularity occurs at the junction and it is interpreted as a brane, the jump brane, of codimension one. We give explicit realization in ten and eleven dimensional supergravity and show that the lower dimensional Planck scale on the brane is finite. The standard model would be trapped on a supersymmetric brane located at the origin whereas the jump brane would surround it at a finite distance. The bulk interactions could transmit the supersymmetry breaking from the jump brane to the SM brane.Comment: 15 pages, LaTeX. v2: misprints corrected in eqs. (5)-(6) and (9); references added. To be published in Phys. Lett.

New theories for the Fermi scale

Electroweak interactions need three Nambu-Goldstone bosons to provide a mass to the W and the Z gauge bosons but they also need an ultra-violet moderator or new physics to unitarize the gauge boson scattering amplitudes. In this talk, I will present various recent models of physics at the Fermi scale: several deformations of the Minimal Supersymmetric Standard Model, Little Higgs models, holographic composite Higgs models, 5D Higgsless models.Comment: 24 pages. Invited review talk at the EPS-HEPP'09 and Lepton-Photon 2009 conference

Neutrino Physics

These lectures aim at providing a pedagogical overview of neutrino physics. We will mostly deal with standard neutrinos, the ones that are part of the Standard Model of particle physics, and with their standard dynamics, which is enough to understand in a coherent picture most of the rich data available. After introducing the basic theoretical framework, we will illustrate the experimental determination of the neutrino parameters and their theoretical implications, in particular for the origin of neutrino masses.Comment: 30 pages, contribution to the 2010 European School of High-Energy Physics; 20 June - 3 July 2010, Raseborg, Finlan

Geometrical approach to duality in N=1 supersymmetric theories

We investigate the geometry of the moduli spaces of dual electric and magnetic N=1 supersymmetric field theories. Using the SU(N_c) gauge group as a guideline we show that the electric and magnetic moduli spaces coincide for a suitable choice of the Kahler potential of the magnetic theory. We analyse the Kahler structure of the dual moduli spaces.Comment: 14 pages, LaTe

Fine Structure Constant Variation from a Late Phase Transition

Recent experimental data indicates that the fine structure constant alpha may be varying on cosmological time scales. We consider the possibility that such a variation could be induced by a second order phase transition which occurs at late times (z ~ 1 - 3) and involves a change in the vacuum expectation value (vev) of a scalar with milli-eV mass. Such light scalars are natural in supersymmetric theories with low SUSY breaking scale. If the vev of this scalar contributes to masses of electrically charged fields, the low-energy value of alpha changes during the phase transition. The observational predictions of this scenario include isotope-dependent deviations from Newtonian gravity at sub-millimeter distances, and (if the phase transition is a sharp event on cosmological time scales) the presence of a well-defined step-like feature in the alpha(z) plot. The relation between the fractional changes in alpha and the QCD confinement scale is highly model dependent, and even in grand unified theories the change in alpha does not need to be accompanied by a large shift in nucleon masses.Comment: 9 pages. V2: discussion on the energy density stored in the scalar oscillations after the phase transition expanded. Typos corrected and Refs. added. Version to appear in PL

Phenomenology of a light scalar: the dilaton

We make use of the language of non-linear realizations to analyze electro-weak symmetry breaking scenarios in which a light dilaton emerges from the breaking of a nearly conformal strong dynamics, and compare the phenomenology of the dilaton to that of the well motivated light composite Higgs scenario. We argue that -- in addition to departures in the decay/production rates into massless gauge bosons mediated by the conformal anomaly -- characterizing features of the light dilaton scenario (as well as other scenarios admitting a light CP-even scalar not directly related to the breaking of the electro-weak symmetry) are off-shell events at high invariant mass involving two longitudinally polarized vector bosons and a dilaton, and tree-level flavor violating processes. Accommodating both electro-weak precision measurements and flavor constraints appears especially challenging in the ambiguous scenario in which the Higgs and the dilaton fields strongly mix. We show that warped higgsless models of electro-weak symmetry breaking are explicit and tractable realizations of this limiting case. The relation between the naive radion profile often adopted in the study of holographic realizations of the light dilaton scenario and the actual dynamical dilaton field is clarified in the Appendix.Comment: 21 page

Supergravity Inspired Warped Compactifications and Effective Cosmological Constants

We propose a supergravity inspired derivation of a Randall-Sundrum's type action as an effective description of the dynamics of a brane coupled to the bulk through gravity only. The cosmological constants in the bulk and on the brane appear at the classical level when solving the equations of motion describing the bosonic sector of supergravities in ten and eleven dimensions coupled to the brane. They are related to physical quantities like the brane electric charge and thus inherit some of their physical properties. The most appealing property is their quantization: in d_\perp extra dimensions, Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical origin also explains the apparent fine-tuning required in the Randall-Sundrum scenario. In our approach, the cosmological constants are derived parameters and cannot be chosen arbitrarily; instead they are determined by the underlying Lagrangian. Some of the branes we construct that support cosmological constant in the bulk have supersymmetric properties: D3-branes of type IIB superstring theory provide an explicit example.Comment: 17 pages, LaTeX, 1 figure. v2: references added and a comment about D-8 brane of massive IIA sugra included v3: improved argument on the effective cosmological constants quantization and clarified discussion on the supersymmetric issue of the solutions constructed. Final version to appear in NP

Classical running of neutrino masses from six dimensions

We discuss a six dimensional mass generation for the neutrinos. Active neutrinos live on a three-brane and interact via a brane localized mass term with a bulk six-dimensional standard model singlet (sterile) Weyl fermion, the two dimensions being transverse to the three-brane. We derive the physical neutrino mass spectrum and show that the active neutrino mass and Kaluza-Klein masses have a logarithmic cutoff divergence related to the zero-size limit of the three-brane in the transverse space. This translates into a renormalisation group running of the neutrino masses above the Kaluza-Klein compactification scale coming from classical effects, without any new non-singlet particles in the spectrum. For compact radii in the eV--MeV range, relevant for neutrino physics, this scenario predicts running neutrino masses which could affect, in particular, neutrinoless double beta decay experiments.Comment: 23 pages, 2 figure