EUROnu-WP6 2010 Report
This is a summary of the work done by the Working Package 6 (Physics) of the EU project "EUROnu" during the second year of activity of the project.
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arXiv subjects
E. Akhmedov
Publications and source records attributed to E. Akhmedov.
Dynamical Left-Right Symmetry Breaking
We study a left--right symmetric model which contains only elementary gauge boson and fermion fields and no scalars. The phenomenologically required symmetry breaking emerges dynamically leading to a composite Higgs sector with a renormalizable effective Lagrangian. We discuss the pattern of symmetry breaking and phenomenological consequences of this scenario. It is shown that a viable top quark mass can be achieved for the ratio of the VEVs of the bi--doublet $\tanβ\equivκ/κ'$ =~ 1.3--4. For a theoretically plausible choice of the parameters the right--handed scale can be as low as $\sim 20 TeV$; in this case one expects several intermediate and low--scale scalars in addition to the \SM Higgs boson. These may lead to observable lepton flavour violation effects including $μ\to eγ$ decay with the rate close to its present experimental upper bound.
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Left-Right Symmetry Breaking in NJL Approach
We study left-right symmetric models which contain only fermion and gauge boson fields and no elementary scalars. The Higgs bosons are generated dynamically through a set of gauge- and parity-invariant 4-fermion operators. It is shown that in a model with a composite bi-doublet and two triplet scalars there is no parity breaking at low energies, whereas in the model with two doublets instead of two triplets parity is broken automatically regardless of the choice of the parameters of the model. For phenomenologically allowed values of the right-handed scale a tumbling symmetry breaking mechanism is realized in which parity breaking at a high scale $μ_R$ propagates down and eventually causes the \EW symmetry breaking at the scale $μ_{EW}\sim 100~GeV$. The model exhibits a number of low and intermediate mass Higgs bosons with certain relations between their masses. In particular, the components of the $SU(2)_L$ Higgs doublet $χ_L$ are pseudo--\GBs of an accidental (approximate) $SU(4)$ symmetry of the Higgs potential and therefore are expected to be relatively light.
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Left-right symmetry and Neutrino Stability
We consider a left-right symmetric model in which neutrinos acquire mass due to the spontaneous violation of both the gauged $B-L$ and a global $U(1)$ symmetry broken by the vacuum expectation value (VEV) of a gauge singlet scalar boson $\VEVσ$. For suitable choices of $\VEVσ$ consistent with all laboratory and astrophysical observations neutrinos will be unstable against majoron emission. All neutrino masses in the keV to MeV range are possible, since the expected neutrino decay lifetimes can be short enough to dilute their relic density below the cosmologically required level. A wide variety of possible new phenomena, associated to the presence of left-right symmetry and/or the global symmetry at the TeV scale, could therefore be observable, without conflict with cosmology. The latter includes the possibility of invisibly decaying higgs bosons, which can be searched at LEP, NLC and LHC.
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Matter Effects in Atmospheric Neutrino Oscillations
The Kamiokande II and IMB data on contained events induced by atmospheric neutrinos exhibit too low a ratio of muons to electrons, which has been interpreted as a possible indication of neutrino oscillations. At the same time, the recent data on upward--going muons in underground detectors have shown no evidence for neutrino oscillations, strongly limiting the allowed region of oscillation parameter space. In this paper we confront different types of neutrino oscillation hypotheses with the experimental results. The matter effects in $ν_μ\leftrightarrow ν_e$ and in $ν_μ\leftrightarrow ν_{sterile}$ oscillations are discussed and shown to affect significantly the upward--going muons.
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