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Guido Altarelli

Publications and source records attributed to Guido Altarelli.

At least 37 records · Page 2Linked to original sources
arXiv2010

Discrete Flavor Symmetries and Models of Neutrino Mixing

We review the application of non abelian discrete groups to the theory of neutrino masses and mixing, which is strongly suggested by the agreement of the Tri-Bimaximal mixing pattern with experiment. After summarizing the motivation and the formalism, we discuss specific models, based on A4, S4 and other finite groups, and their phenomenological implications, including lepton flavor violating processes, leptogenesis and the extension to quarks. In alternative to Tri-Bimaximal mixing the application of discrete flavor symmetries to quark-lepton complementarity and Bimaximal Mixing is also considered.

hep-ph↗
arXiv2010

The Electroweak Symmetry Breaking Riddle

I present a concise review of the Higgs problem which plays a central role in particle physics today. The Higgs of the minimal Standard Model is so far just a conjecture that needs to be verified or discarded at the LHC. Probably the reality is more complicated. I will summarize the motivation for New Physics that should accompany or even replace the Higgs discovery and a number of its possible forms that could be revealed by the LHC

hep-ph↗
arXiv2010

Particle Physics in the LHC Era and beyond

I present a concise review of where we stand in particle physics today. First, I will discuss QCD, then the electroweak sector and finally the motivations and the avenues for new physics beyond the Standard Model.

hep-ph↗
arXiv2009

DIS 2009 Concluding Talk: Outlook and Perspective

I will present here my perception on the status of Deep Inelastic Scattering physics, as I have further developed it during this Workshop, together with a number of comments on the results that have impressed me most during this week. I will emphasize a number of open problems and of critical areas. Finally I conclude with some projections and auspices for the future of the field.

hep-ph↗
arXiv2009

Towards small x resummed DIS phenomenology

We report on recent progress towards quantitative phenomenology of small x resummation of deep-inelastic structure functions. We compute small x resummed K-factors with realistic PDFs and estimate their impact in the HERA kinematical region. These K-factors, which match smoothly to the fixed order NLO results, approximately reproduce the effect of a small x resummed PDF analysis. Typical corrections are found to be of the same order as the NNLO ones, that is, a few percent, but with opposite sign. These results imply that resummation corrections could be relevant for a global PDF analysis, especially with the very precise combined HERA dataset.

hep-ph↗
arXiv2009

Theoretical Models of Neutrino Mixing: Recent Developments

The data on neutrino mixing are at present compatible with Tri-Bimaximal (TB) mixing. If one takes this indication seriously then the models that lead to TB mixing in first approximation are particularly interesting and A4 models are prominent in this list. However, the agreement of TB mixing with the data could still be an accident. We discuss a recent model based on S4 where Bimaximal mixing is instead valid at leading order and the large corrections needed to reproduce the data arise from the diagonalization of charged leptons. The value of $θ_{13}$ could distinguish between the two alternatives.

hep-ph↗
arXiv2009

A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing

We present a see-saw $A_4$ model for Tri-Bimaximal mixing which is based on a very economical flavour symmetry and field content and still possesses all the good features of $A_4$ models. In particular the charged lepton mass hierarchies are determined by the $A_4\times Z_4$ flavour symmetry itself without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is exact in leading order while all the mixing angles receive corrections of the same order in next-to-the-leading approximation. As a consequence the predicted value of $θ_{13}$ is within the sensitivity of the experiments which will take data in the near future. The light neutrino spectrum, typical of $A_4$ see-saw models, with its phenomenological implications, also including leptoproduction, is studied in detail.

hep-ph↗
arXiv2009

Particle Physics at the LHC Start

I present a concise review of where we stand in particle physics today. First, I will discuss the status of the Standard Model, its open problems and the expected answers from the LHC. Then I will briefly review the avenues for New Physics that can be revealed by the LHC.

hep-ph↗
arXiv2009

Can we trust small x resummation?

We review the current status of small x resummation of evolution of parton distributions and of deep-inelastic coefficient functions. We show that the resummed perturbative expansion is stable, robust upon different treatments of subleading terms, and that it matches smoothly to the unresummed perturbative expansions, with corrections which are of the same order as the typical NNLO ones in the HERA kinematic region. We discuss different approaches to small x resummation: we show that the ambiguities in the resummation procedure are small, provided all parametrically enhanced terms are included in the resummation and properly matched.

hep-ph↗
arXiv2008

CP violation in neutrino oscillations and new physics

We consider future experiments to detect CP violation in neutrino oscillations and discuss how to test that all asymmetries are indeed described in terms of the single leptonic Jarlskog invariant as predicted in the absence of new physics effects.

hep-ph↗
arXiv2008

New Physics and the LHC

In these lectures I start by briefly reviewing the status of the electroweak theory, in the Standard Model and beyond. I then discuss the motivation and the possible avenues for new physics, on the brink of the LHC start.

hep-ph↗
arXiv2008

Structure Function Resummation in small-x QCD

We summarize our recent results on small x resummation in full QCD with n_f quark flavours and discuss their phenomenological impact in the extraction of parton distributions from present day structure function data and their extrapolation to the kinematics relevant for future colliders such as the LHC.

hep-ph↗
arXiv2008

A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4

We discuss a grand unified model based on SUSY SU(5) in extra dimensions and on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing for neutrinos with the accuracy required by the data, also leads to a natural description of the observed pattern of quark masses and mixings.

hep-ph↗
arXiv2008

Small x Resummation with Quarks: Deep-Inelastic Scattering

We extend our previous results on small-x resummation in the pure Yang--Mills theory to full QCD with nf quark flavours, with a resummed two-by-two matrix of resummed quark and gluon splitting functions. We also construct the corresponding deep-inelastic coefficient functions, and show how these can be combined with parton densities to give fully resummed deep-inelastic structure functions F_2 and F_L at the next-to-leading logarithmic level. We discuss how this resummation can be performed in different factorization schemes, including the commonly used MSbar scheme. We study the importance of the resummation effects by comparison with fixed-order perturbative results, and we discuss the corresponding renormalization and factorization scale variation uncertainties. We find that for x below 0.01 the resummation effects are comparable in size to the fixed order NNLO corrections, but differ in shape. We finally discuss the phenomenological impact of the small-x resummation, specifically in the extraction of parton distribution from present day experiments and their extrapolation to the kinematics relevant for future colliders such as the LHC

hep-ph↗
arXiv2007

Lectures on Models of Neutrino Masses and Mixings

We present a concise review of models for neutrino masses and mixings with particular emphasis on recent developments and current problems. We discuss in detail attempts at reproducing approximate tri-bimaximal mixing starting from discrete symmetry groups, notably A4. We discuss the problems encountered when trying to extend the symmetry to the quark sector and to construct Grand Unified versions.

hep-ph↗
arXiv2007

Models of Neutrino Masses and Mixings: a Progress Report

We present some recent developments on model building for neutrino masses and mixings. In particular, we review tri-bimaximal neutrino mixing derived from discrete groups, notably A4. We discuss the problems encountered with extending the symmetry to the quark sector and with Grand Unification.

hep-ph↗