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Models of little Higgs and electroweak precision tests

Description: The little Higgs idea is an alternative to supersymmetry as a solution to the gauge hierarchy problem. In this note, the author reviews various little Higgs models and their phenomenology with emphasis on the precision electroweak constraints in these models.
Date: January 1, 2006
Creator: Chen, Mu-Chun
Partner: UNT Libraries Government Documents Department

TASI 2006 Lectures on Leptogenesis

Description: The origin of the asymmetry between matter and anti-matter of the Universe has been one of the great challenges in particle physics and cosmology. Leptogenesis as a mechanism for generating the cosmological baryon asymmetry of the Universe has gained significant interests ever since the advent of the evidence of non-zero neutrino masses. In these lectures presented at TASI 2006, I review various realizations of leptogenesis and allude to recent developments in this subject.
Date: March 1, 2007
Creator: Chen, Mu-Chun & /Fermilab /UC, Irvine
Partner: UNT Libraries Government Documents Department

Lepton Flavor Violation in Predictive SUSY-GUT Models

Description: There have been many theoretical models constructed which aim to explain the neutrino masses and mixing patterns. While many of the models will be eliminated once more accurate determinations of the mixing parameters, especially sin{sup 2} 2{theta}{sub 13}, are obtained, charged lepton flavor violation (LFV) experiments are able to differentiate even further among the models. In this paper, they investigate various rare LFV processes, such as {ell}{sub i} {yields} {ell}{sub j} + {gamma} and {mu} - e conversion, in five predictive SUSY SO(10) models and their allowed soft SUSY breaking parameter space in the constrained minimal SUSY standard model (CMSSM). Utilizing the WMAP dark matter constraints, they obtain lower bounds on the branching ratios of these rare processes and find that at least three of the five models they consider give rise to predictions for {mu} {yields} e + {gamma} that will be tested by the MEG collaboration at PSI. in addition, the next generation {mu} - e conversion experiment has sensitivity to the predictions of all five models, making it an even more robust way to test these models. While generic studies have emphasized the dependence of the branching ratios of these rare processes on the reactor neutrino angle, {theta}{sub 13}, and the mass of the heaviest right-handed neutrino, M{sub 3}, they find very massive M{sub 3} is more significant than large {theta}{sub 13} in leading to branching ratios near to the present upper limits.
Date: February 1, 2008
Creator: Albright, Carl H. & Chen, Mu-Chun
Partner: UNT Libraries Government Documents Department

Low scale seesaw, electron EDM and leptogenesis in a model with spontaneous CP violation

Description: Strong correlations between leptogenesis and low energy CP violating leptonic processes have been shown by us to exist fin the minimal left-right symmetric model with spontaneous CP violation. In this note, they investigate the implications of this model for the electric dipole moment of the electron. With an additional broken U(1){sub H} symmetry, the seesaw scale can be lowered to close to the electroweak scale. This additional symmetry also makes the connection between CP violation in quark sector to that in the lepton sector possible.
Date: September 1, 2006
Creator: Chen, Mu-Chun; /Fermilab /UC, Irvine; Mahanthappa, K.T. & U., /Colorado
Partner: UNT Libraries Government Documents Department

Higgs triplets and limits from precision measurements

Description: In this letter, they present the results on a global fit to precision electroweak data in a Higgs triplet model. In models with a triplet Higgs boson, a consistent renormalization scheme differs from that of the Standard Model and the global fit shows that a light Higgs boson with mass of 100-200 GeV is preferred. Triplet Higgs bosons arise in many extensions of the Standard Model, including the left-right model and the Little Higgs models. The result demonstrates the importance of the scalar loops when there is a large mass splitting between the heavy scalars. It also indicates the significance of the global fit.
Date: April 1, 2006
Creator: Chen, Mu-Chun; /Fermilab; Dawson, Sally; Krupovnickas, Tadas & /Brookhaven
Partner: UNT Libraries Government Documents Department

Gauge Trimming of Neutrino Masses

Description: We show that under a new U(1) gauge symmetry, which is non-anomalous in the presence of one ''right-handed neutrino'' per generation and consistent with the standard model Yukawa couplings, the most general fermion charges are determined in terms of four rational parameters. This generalization of the B-L symmetry with generation-dependent lepton charges leads to neutrino masses induced by operators of high dimensionality. Neutrino masses are thus naturally small without invoking physics at energies above the TeV scale, whether neutrinos are Majorana or Dirac fermions. This ''Leptocratic'' Model predicts the existence of light quasi-sterile neutrinos with consequences for cosmology, and implies that collider experiments may reveal the origin of neutrino masses.
Date: December 1, 2006
Creator: Chen, Mu-Chun; de Gouvea, Andre & Dobrescu, Bogdan A.
Partner: UNT Libraries Government Documents Department

Theory of neutrinos: A White paper

Description: During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ''The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report [1] provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.
Date: October 1, 2005
Creator: Mohapatra, R.N.; Antusch, S.; Babu, K.S.; Barenboim, G.; Chen, Mu-Chun; Davidson, S. et al.
Partner: UNT Libraries Government Documents Department

Theory of Neutrinos: a White Paper

Description: During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ''The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report [1] provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.
Date: January 11, 2006
Creator: Mohapatra, R.N.; Antusch, S.; Babu, K.S.; Barenboim, G.; Chen, Mu-Chun; Davidson, S. et al.
Partner: UNT Libraries Government Documents Department