scholarly journals SUPERSTRING MODELS CHALLENGED BY RARE PROCESSES

1987 ◽  
Vol 02 (03) ◽  
pp. 831-890 ◽  
Author(s):  
B. A. CAMPBELL ◽  
J. ELLIS ◽  
K. ENQVIST ◽  
M. K. GAILLARD ◽  
D. V. NANOPOULOS
Keyword(s):  
Upper Bounds ◽  
Low Energy ◽  
Neutrino Masses ◽  
Dynamical Models ◽  
Gauge Bosons ◽  
Yukawa Couplings ◽  
Flavor Changing ◽  
The Standard Model ◽  
New Interactions ◽  
Matter Fields

Superstring models compactified on Calabi–Yau manifolds contain additional matter fields and gauge bosons beyond those in the Standard Model. The new matter and gauge couplings would make additional contributions to conventional electroweak processes, generate extra flavor-changing neutral interactions, and mediate new interactions leading to proton decay and neutrino masses. We use the phenomenological constraints on such effects to derive upper bounds on Yukawa couplings in low-energy dynamical models inspired by the superstring. We draw attention to the processes which give the best bounds on new Yukawa couplings, and which are those where novel superstring effects might first appear as experimental sensitivity is improved. Our bounds are not sufficient to exclude most superstring models with additional light particles, but do suggest that some couplings are too small to realize certain scenarios for symmetry breaking by radiative corrections.

TECHNIDILATON OR HIGGS?

1993 ◽  
Vol 08 (03) ◽  
pp. 275-283 ◽  
Author(s):  
EDI HALYO
Keyword(s):  
Standard Model ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Higgs Bosons ◽  
Low Energy ◽  
Gauge Bosons ◽  
Effective Lagrangian ◽  
The Standard Model

Interactions of the technidilaton with fermions and gauge bosons are obtained by constructing a low energy effective Lagrangian and using the fact that the technidilaton couples to the trace of the energy-momentum tensor Θµµ. Technidilaton’s interactions are compared with those of the Higgs bosons of the Standard Model with one or two scalar doublets.

scholarly journals From old symmetries to new symmetries: Quarks, leptons and B-L

2014 ◽  
Vol 29 (29) ◽  
pp. 1430066 ◽  
Author(s):  
Rabindra N. Mohapatra
Keyword(s):  
Standard Model ◽  
Weak Interactions ◽  
Low Energy ◽  
Neutrino Masses ◽  
Beyond The Standard Model ◽  
The Standard Model ◽  
Recent Developments

The Baryon–Lepton difference (B-L) is increasingly emerging as a possible new symmetry of the weak interactions of quarks and leptons as a way to understand the small neutrino masses. There is the possibility that current and future searches at colliders and in low energy rare processes may provide evidence for this symmetry. This paper provides a brief overview of the early developments that led to B-L as a possible symmetry beyond the standard model, and also discusses some recent developments.

scholarly journals Predictions forμ→eγin Supersymmetry from Nontrivial Quark-Lepton Complementarity and Flavor Symmetry

2007 ◽  
Vol 2007 ◽  
pp. 1-17 ◽  
Author(s):  
Marco Picariello
Keyword(s):  
Experimental Data ◽  
Correlation Matrix ◽  
Low Energy ◽  
The Other ◽  
Neutrino Masses ◽  
Flavor Symmetry ◽  
Dirac Neutrino ◽  
Yukawa Couplings ◽  
Energy Neutrino ◽  
Lepton Decays

We compute the effect of nondiagonal neutrino mass inli→ljγin Supersymmetry (SUSY) theories with nontrivial quark-lepton complementarity and a flavor symmetry. The correlation matrixVM=UCKMUPMNSis such that its (1,3) entry, as preferred by the present experimental data, is zero. We do not assume thatVMis bimaximal. Quark-lepton complementarity and the flavor symmetry strongly constrain the theory and we obtain a clear prediction for the contribution toμ→eγand theτdecaysτ→eγandτ→μγ. If the Dirac neutrino Yukawa couplings are degenerate but the low-energy neutrino masses are not degenerate, then the lepton decays are related among them by theVMentries. On the other hand, if the Dirac neutrino Yukawa couplings are hierarchical or the low-energy neutrino masses are degenerate, then the prediction for the lepton decays comes from theUCKMhierarchy.

The Bs0 meson decaying into τe mediated by Z′ gauge bosons

2021 ◽  
pp. 2150167
Author(s):  
J. I. Aranda ◽  
E. Cruz-Albaro ◽  
D. Espinosa-Gómez ◽  
J. Montaño ◽  
F. Ramírez-Zavaleta ◽  
...  
Keyword(s):  
Gauge Boson ◽  
Conversion Rate ◽  
Branching Ratio ◽  
Upper Bounds ◽  
Experimental Results ◽  
The Other ◽  
Experimental Measurements ◽  
Gauge Bosons ◽  
Flavor Changing ◽  
First Time

We calculate bounds for the branching ratio of the [Formula: see text] decay, for the first time, in the context of flavor changing neutral currents mediated by a [Formula: see text] gauge boson, which can arise from five extended models. In this sense, by using experimental measurements on the [Formula: see text] decay and the [Formula: see text] process, we look for constraints of the [Formula: see text] coupling, where the more restrictive bound is offered by the last one. On the other hand, by employing the experimental restriction on the [Formula: see text] decay, the strength of the [Formula: see text] coupling is estimated. Our analysis is based on the more recent experimental results on searches for the [Formula: see text] gauge boson in ATLAS and CMS detectors. In addition, we revisited the [Formula: see text] meson decays by using different approaches not previously reported. The strengths of the [Formula: see text] and [Formula: see text] couplings were estimated by employing experimental restrictions on the [Formula: see text] decay and the [Formula: see text] conversion rate, respectively. Thus, we predict the following upper bounds: [Formula: see text], [Formula: see text] and [Formula: see text].

scholarly journals EXTENDING THE STANDARD MODEL: AN UPPER BOUND FOR A NEUTRINO MASS FROM THE RARE DECAY $K^+\rightarrow\pi^+\nu\bar\nu$

2000 ◽  
Vol 15 (08) ◽  
pp. 579-586 ◽  
Author(s):  
B. MACHET
Keyword(s):  
Standard Model ◽  
Neutrino Mass ◽  
Upper Bound ◽  
Average Rate ◽  
Rare Decay ◽  
Yukawa Couplings ◽  
Flavor Changing ◽  
Upper Limit ◽  
Quartic Term ◽  
The Standard Model

The standard model seeming at a loss to account for the present experimental average rate for the rare decay [Formula: see text], we tackle the question with the extension of the Glashow–Salam–Weinberg model to an SU (2)L× U (1) gauge theory of J = 0 mesons proposed in Ref. 7, in which, in addition, the neutrinos are given Dirac masses from Yukawa couplings to the Higgs boson. The latter triggers a new contribution to this decay through flavor changing neutral currents that arise in the quartic term of the symmetry breaking potential; it becomes sizable for a neutrino mass in the MeV range; the experimental upper limit for the decay rate translates into an upper bound of 5.5 MeV for the mass of the neutrino, three times lower than the present direct bounds.

scholarly journals Exotic leptons: Collider and muon magnetic moment constraints

2015 ◽  
Vol 30 (32) ◽  
pp. 1550187 ◽  
Author(s):  
D. Cogollo
Keyword(s):  
Magnetic Moment ◽  
Neutral Current ◽  
Gauge Bosons ◽  
Flavor Changing ◽  
Ongoing Effort ◽  
The Standard Model ◽  
Flavor Changing Neutral Current ◽  
Charged Leptons ◽  
Muon Magnetic Moment ◽  
The Masses

In light of the ongoing effort on reducing the theoretical uncertainties and an upcoming experiment concerning muon magnetic moment, we perform a detailed study of an 3-4-1 electroweak gauge extension of the standard model that contains exotic charged leptons in its spectrum. We discuss flavor changing neutral current, collider and electroweak bounds on the model and derive [Formula: see text] limits using current and projected limits on the muon magnetic moment. In summary, we exclude the masses of new gauge bosons that couple to muons and heavy charged leptons up to 700 GeV. Moreover, we find a projected lower bound on the scale of symmetry breaking to be 2 TeV.

scholarly journals CP violation in the lepton sector and implications for leptogenesis

2018 ◽  
Vol 33 (05n06) ◽  
pp. 1842006 ◽  
Author(s):  
C. Hagedorn ◽  
R. N. Mohapatra ◽  
E. Molinaro ◽  
C. C. Nishi ◽  
S. T. Petcov
Keyword(s):  
Cp Violation ◽  
Standard Model ◽  
Low Energy ◽  
Current Status ◽  
Neutrino Masses ◽  
Flavor Symmetry ◽  
Lepton Sector ◽  
The Standard Model ◽  
Mixing Matrix ◽  
Cp Symmetry

We review the current status of the data on neutrino masses and lepton mixing and the prospects for measuring the CP-violating phases in the lepton sector. The possible connection between low energy CP violation encoded in the Dirac and Majorana phases of the Pontecorvo–Maki–Nakagawa–Sakata mixing matrix and successful leptogenesis is emphasized in the context of seesaw extensions of the Standard Model with a flavor symmetry [Formula: see text] (and CP symmetry).

scholarly journals Constraints on the U(1)L gauge boson in a wide mass range

2016 ◽  
Vol 31 (11) ◽  
pp. 1650059 ◽  
Author(s):  
Yu Seon Jeong ◽  
C. S. Kim ◽  
Hye-Sung Lee
Keyword(s):  
Standard Model ◽  
Gauge Boson ◽  
Mass Range ◽  
Small Mass ◽  
Low Energy ◽  
Gauge Bosons ◽  
Dark Photon ◽  
The Standard Model ◽  
Similarities And Differences ◽  
New Discovery

There is a growing interest for the search of new light gauge bosons. The small mass of a new boson can turn various kinds of low-energy experiments to a new discovery machine, depending on their couplings to the Standard Model particles. It is important to understand the properties of each type of gauge boson and their current constraints for a given mass. While the dark photon (which couples to the electric charges) and the [Formula: see text] gauge boson have been well studied in an extensive mass range, the [Formula: see text] gauge boson has not been fully investigated yet. We consider the gauge boson of the [Formula: see text] in a wide mass range [Formula: see text] and investigate the constraints on its coupling from various experiments, discussing the similarities and differences from the dark photon and the [Formula: see text] gauge boson.

scholarly journals Doublet–singlet model and unitarity

2016 ◽  
Vol 31 (01) ◽  
pp. 1650013 ◽  
Author(s):  
G. Cynolter ◽  
J. Kovács ◽  
E. Lendvai
Keyword(s):  
Dark Matter ◽  
Mass Spectrum ◽  
Scattering Amplitudes ◽  
Standard Model ◽  
Dark Matter Candidate ◽  
Particle Scattering ◽  
Gauge Bosons ◽  
Yukawa Couplings ◽  
The Standard Model ◽  
Blind Spots

We study the renormalizable singlet–doublet fermionic extension of the Standard Model (SM). In this model, the new vector-like fermions couple to the gauge bosons and to the Higgs via new Yukawa couplings that allow for nontrivial mixing in the new sector, providing a stable, neutral dark matter candidate. Approximate analytic formulae are given for the mass spectrum around the blind spots, where the dark matter candidate coupling to h or Z vanishes. We calculate the two particle scattering amplitudes in the model, impose the perturbative unitarity constraints and establish bounds on the Yukawa couplings.

scholarly journals A NewS4Flavor Symmetry in 3-3-1 Model with Neutral Fermions

2014 ◽  
Vol 2014 ◽  
pp. 1-24 ◽  
Author(s):  
V. V. Vien ◽  
H. N. Long
Keyword(s):  
Scalar Potential ◽  
Neutrino Masses ◽  
Neutrino Mixing ◽  
Gauge Bosons ◽  
Quark Masses ◽  
Model Based ◽  
Fermion Masses ◽  
The Standard Model ◽  
Mixing Matrix ◽  
The Difference

A newS4flavor model based onSU(3)C⊗SU(3)L⊗U(1)Xgauge symmetry responsible for fermion masses and mixings is constructed. The neutrinos get small masses from only an antisextet ofSU(3)Lwhich is in a doublet underS4. In this work, we assume the VEVs of the antisextet differ from each other underS4and the difference of these VEVs is regarded as a small perturbation, and then the model can fit the experimental data on neutrino masses and mixings. Our results show that the neutrino masses are naturally small and a deviation from the tribimaximal neutrino mixing form can be realized. The quark masses and mixing matrix are also discussed. The number of required Higgs multiplets is less and the scalar potential of the model is simpler than those of the model based onS3and our previousS4model. The assignation of VEVs to antisextet leads to the mixing of the new gauge bosons and those in the standard model. The mixing in the charged gauge bosons as well as the neutral gauge bosons is considered.

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