Zurab Berezhiani

The early mirror universe: inflation, baryogenesis, nucleosynthesis and dark matter

Abstract There can exist a parallel ‘mirror’ world which has the same particle physics as the observable world and couples the latter only gravitationally. The nucleosynthesis bounds demand that the mirror sector should have a smaller temperature than the ordinary one. By this reason its evolution should be substantially deviated from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. Starting from an inflationary scenario which could explain the different initial temperatures of the two sectors, we study the time history of the early mirror universe. In particular, we show that in the context of the GUT or electroweak baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one and in fact the mirror baryons could provide the dominant dark matter component of the universe. In addition, analyzing the nucleosynthesis epoch, we show that the mirror helium abundance should be much larger than that of ordinary helium. The implications of the mirror baryons representing a kind of self-interacting dark matter for the large scale structure formation, the CMB anysotropy, the galactic halo structures, microlensing, etc. are briefly discussed.

Planck scale physics and neutrino masses

We discuss gravitationally induced masses and mass splittings of Majorana, Zeldovich-Konopinski-Mahmoud, and Dirac neutrinos. Among other implications, these effects can provide a solution of the solar neutrino puzzle. In particular, we show how this may work in the 17 keV neutrino picture.

Limits on the non-standard interactions of neutrinos from e+e− colliders

Abstract We provide an effective Lagrangian analysis of contact non-standard interactions of neutrinos with electrons, which can be effectively mediated by extra particles, and examine the associated experimental limits. At present, such interactions are strongly constrained only for νμ: the bounds are loose for νe and absent for ντ. We emphasize the unique role played by the reaction e + e − →ν ν γ in providing direct constraints on such non-standard interactions.

Spontaneous Lorentz Breaking and Massive Gravity

Theories with an extra spin-two field coupled to gravity admit a massive phase with broken Lorentz symmetry. While the equivalence principle is respected, the Newtonian potentials are in general modified, but they may be protected by a scale symmetry of the coupling term. The gravitational waves phenomenology is quite rich: two gravitons, one massive and one massless, oscillate and propagate with distinct velocities, different from the speed of light. A time of flight difference between gravitons and photons from a common source would provide a clear signal of this theory.

Exact Spherically Symmetric Solutions in Massive Gravity

A phase of massive gravity free from pathologies can be obtained by coupling the metric to an additional spin-two field. We study the gravitational field produced by a static spherically symmetric body, by finding the exact solution that generalizes the Schwarzschild metric to the case of massive gravity. Besides the usual 1/r term, the main effects of the new spin-two field are a shift of the total mass of the body and the presence of a new power-like term, with sizes determined by the mass and the shape (the radius) of the source. These modifications, being source dependent, give rise to a dynamical violation of the Strong Equivalence Principle. Depending on the details of the coupling of the new field, the power-like term may dominate at large distances or even in the ultraviolet. The effect persists also when the dynamics of the extra field is decoupled.

Predictive Grand Unified Textures for Quark and Neutrino Masses and Mixings

Abstract We propose new textures for the fermion Yukawa matrices which are generalizations of the so-called Stech ansatz. We discuss how these textures can be realized in supersymmetric grand unified models with horizontal symmetry SU(3) H among the fermion generations. In this framework the mass and mixing hierarchy of fermions (including neutrinos) can emerge in a natural way. We emphasize the central role played by the SU(3) H adjoint Higgs field which reduces SU(3) H to U(2) H at the GUT scale. A complete SO(10)×SU(3) H model is presented in which the desired Yukawa textures can be obtained by symmetry reasons. The phenomenological implications of these textures are thoroughly investigated. Among various realistic possibilities for the Clebsch factors between the quark and lepton entries, we find three different solutions which provide excellent fits of the quark masses and CKM mixing angles. Interestingly, all these solutions predict the correct amount of CP violation via the CKM mechanism, and, in addition, lead to an appealing pattern of the neutrino masses and mixing angles. In particular, they all predict nearly maximal 23 mixing and small 12 mixing in the lepton sector, respectively, in the range needed for the explanation of the atmospheric and solar neutrino anomaly.

Could the supersymmetric Higgs particles naturally be pseudo-Goldstone bosons?☆

Abstract The doublet-triplet splitting problem is perhaps the most problematic aspect of supersymmetric grand unified theories. It can be argued that the most natural reason for the Higgs doublets to be light is that they are pseudo-Goldstone bosons associated with the spontaneous breakdown of an accidental global symmetry. In this paper we discuss the possibility of implementing this idea in the SU(6) model of Refs. [ 11–14]. We show that although it is simple to generate an accidental symmetry of the renormalizable terms of the potential, it is quite difficult to construct a model which allows for the preservation of the accidental symmetry in the nonrenormalizable terms. We summarize the constraints on such models and then give three different ways to construct a super-potential where the dangerous mixing terms are sufficiently suppressed even in the presence of nonrenormalizable operators. With these examples we demonstrate the existence of consistent models implementing the Higgs as pseudo-Goldstone boson scheme. We extend one of the three examples to include fermion masses. We also show that when restricted to regular group embeddings the only possible models without light triplets are trivial generalizations of the SU(6) model we consider.

UNIFIED PICTURE OF THE PARTICLE AND SPARTICLE MASSES IN SUSY GUT

Abstract The horizontal symmetry U(3)H can greatly help in solving the flavour problem in supersymmetric grand unification. For demonstration we revisit the SU(5)×U(3)H model suggested earlier by Z. Berezhiani [Phys. Lett. B 150 (1985) 177] and show that it can lead to a consistent picture of masses and mixing in both the fermion and sfermion sectors. In this model, under simple and natural assumptions on the heavy fermion content (only 10+ 10 states) and the supersymmetry breaking features (so called proportionality condition), all soft parameters appear to be related to the MSSM Yukawa constants in a very remarkable way, and all dangerous supersymmetric flavour-changing effects are naturally suppressed. The horizontal symmetry can be regarded as a local symmetry in a consistent way (without D-term problem), if one introduces the mirror SU(5)′ sector of the particles and interactions completely analogous to that in the visible SU(5) sector.

More missing VEV mechanism in supersymmetric SO(10) model

Abstract The anomalous gauge U(1)A symmetry can be a very useful ingredient towards building the complete supersymmetric SO(10) theory. We present an example of the SO(10) × U(1)A model which provides “all order” solution to the doublet-triplet splitting problem via the missing VEV mechanism. An interesting feature of the model is that all relevant GUT scales are related to a single dimensional parameter in the Higgs superpotential, which could have a dynamical origin. In this situation the SO(10) symmetry breaks down to the MSSM practically at one step, without intermediate stages. We also present a variant of the model where the colour Higgsino mediated d = 5 operators are naturally suppressed. We also extend the model by implementing U(1)A as a horizontal symmetry for explaining the fermion mass and mixing hierarchy. The obtained pattern of the fermion mass matrices implies a moderate value of tan β (∼ 6–10) and leads to the consistent picture for the low energy observables. It also suggests the neutrino mass and mixing pattern that could naturally explain both the solar and atmospheric neutrino problems, respectively through the νe-νμ and νμ-ντ oscillations.

Double Protection of the Higgs Potential in a Supersymmetric Little Higgs Model

A mechanism of double protection of the Higgs potential, by supersymmetry and by a global symmetry, is investigated in a class of supersymmetric models with the SU(3)cxSU(3)wxU(1)x gauge symmetry. The electroweak symmetry can be then broken with no fine-tuning at all.