555 research outputs found

### 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

### 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

### 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

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