Broken Family Symmetry Research Articles

FCNC-free multi-Higgs-doublet models from broken family symmetries

We demonstrate how residual flavour symmetries, infrared signatures of symmetry breaking in complete models of flavour, can naturally forbid (or limit in a flavour specific way) flavour-changing neutral currents (FCNC) in multi-Higgs-doublet models (MHDM) without using mass hierarchies. We first review how this model-independent mechanism can control the fermionic mixing patterns of the Standard Model, and then implement the symmetries in the Yukawa sector of MHDM, which allows us to intimately connect the predictivity of a given flavour model with its ability to sequester FCNC. Finally, after discussing various subtleties of the approach, we sketch an A4 toy model that realises an explicit example of these simplified constructions.

Phenomenological constraints on low-scale gravity

We study the constraints on gravity scale ${M}_{P}$ in extra-dimension gravitational theory, obtained from gravity-induced processes. The obtained constraints are subdivided into strong (though not robust) and reliable (though less strong). The strong constraints can be in principle relaxed due to some broken gauge symmetries, e.g. family symmetry. The strongest constraint is given by neutrino oscillations. For different assumptions the lower bound on ${M}_{P}$ is ${10}^{15}--{10}^{18}\text{ }\text{ }\mathrm{GeV}$. However, it can be, in principle, reduced by broken family symmetry. More reliable bounds are due to flavor-conserved operators or those which change the flavors within one family. These bounds, obtained using the electron mass and width of $\ensuremath{\pi}\ensuremath{\rightarrow}e\ensuremath{\nu}$ decay, are $1\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{ }\mathrm{GeV}$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{ }\mathrm{GeV}$, for these two cases, respectively.

Kähler corrections and softly broken family symmetries

Spontaneously broken family symmetry provides a promising origin for the observed quark and lepton mass and mixing angle structure. In a supersymmetric theory such structure comes from a combination of the contributions from the superpotential and the K\"{a}hler potential. The superpotential effects have been widely studied but relatively little attention has been given to the effects of the K\"{a}hler sector. In this paper we develop techniques to simplify the analysis of such K\"{a}hler effects. Using them we show that in the class of theories with an hierarchical structure for the Yukawa couplings the K\"{a}hler corrections to both the masses and mixing angles are subdominant. This is true even in cases that texture zeros are filled in by the terms coming from the K\"{a}hler potential.

Cosmoparticle physics as the physical basis for modern cosmology

Abstract Cosmoparticle physics has appeared as a natural result of the internal development of cosmology, looking for physical grounds for inflation, baryosynthesis and nonbaryonic dark matter, and of particle physics, going beyond the standard model of particle interactions. Its aim is to study the physical basis of modern cosmology in the combination of indirect cosmological, astrophysical and physical effects. The ideas of new particles and fields, predicted by particle theory, and on their cosmological impact are discussed, as well as the methods of cosmoparticle physics to probe these ideas are considered with special analysis of physical mechanisms for inflation, baryosynthesis and nonbaryonic dark matter. These mechanisms are shown to reflect the main principle of modern cosmology, putting instead of formal parameters of cosmological models physical processes governing the evolution of Big Bang Universe. Their realization on the basis of particle theory induces additional model-dependent predictions, accessible to various methods of cosmoparticle physics. The power of these methods is illustrated in the example of a gauge model with broken family symmetry, on which the horizontal unification is based, possessing quantitatively date physical grounds for inflation, baryosynthesis and effectively multicomponent dark matter scenarios.

Physically self-consistent basis for modern cosmology

Cosmoparticle physics appeared as a natural result of internal development of cosmology seeking physical grounds for inflation, baryosynthesis, and nonbaryonic dark matter and of particle physics going outside the Standard Model of particle interactions. Its aim is to study the foundations of particle physics and cosmology and their fundamental relationship in the combination of respective indirect cosmological, astrophysical, and physical effects. The ideas on new particles and fields predicted by particle theory and on their cosmological impact are discussed, as well as the methods of cosmoparticle physics to probe these ideas, are considered with special analysis of physical mechanisms for inflation, baryosynthesis, and nonbaryonic dark matter. These mechanisms are shown to reflect the main principle of modern cosmology, putting, instead of formal parameters of cosmological models, physical processes governing the evolution of the big-bang universe. Their realization on the basis of particle theory induces additional model-dependent predictions, accessible to various methods of nonaccelerator particle physics. Probes for such predictions, with the use of astrophysical data, are the aim of cosmoarcheology studying astrophysical effects of new physics. The possibility of finding quantitatively definite relationships between cosmological and laboratory effects on the basis of cosmoparticle approach, as well as of obtaining a unique solution to the problem of physical candidates for inflation, mechanisms of baryogenesis, and multicomponent dark matter, is exemplified in terms of gauge model with broken family symmetry, underlying horizontal unification and possessing quantitatively definite physical grounds for inflation, baryosynthesis, and effectively multicomponent dark-matter scenarios.

Third generation familons,Bfactories, and neutrino cosmology

We study the physics of spontaneously broken family symmetries acting on the third generation. Massless familons (or Majorons) $f$ associated with such broken symmetries are motivated especially by cosmological scenarios with decaying tau neutrinos. We first note that, in marked contrast with the case for the first two generations, constraints on third generation familon couplings are poor, and are, in fact, non-existent at present in the hadronic sector. We derive new bounds from $B^0$--$\bar{B}^0$ mixing, $B^0 \to l^+ l'^-$, $b\to s\nu\bar{\nu}$, and astrophysics. The resulting constraints on familon decay constants are still much weaker than those for the first and second generation. We then discuss the promising prospects for significant improvements from searches for $\tau\to l f$, $B\to (\pi, K) f$, and $b\to (d,s) f$ with the current CLEO, ARGUS, and LEP data. Finally, we note that future constraints from CLEO III and the $B$ factories will probe decay constants beyond 10^8 GeV, well within regions of parameter space favored by proposed scenarios in neutrino cosmology.

Systematic SO(10) operator analysis for fermion masses.

A new approach for deducing the theory of fermion masses at the scale of grand unification is proposed. Combining SO(10) grand unification, family symmetries and supersymmetry with a systematic operator analysis, the minimal set of fermion mass operators consistent with low energy data is determined. Exploiting the full power of SO(10) to relate up, down and charged lepton mass matrices, we obtain predictions for 7 of the mass and mixing parameters. The assumptions upon which the operator search and resulting predictions are based are stressed, together with a discussion of how the predictions are affected by a relaxation of some of the assumptions.The masses of the heaviest generation, $m_t,m_b$ and $m_\tau$, are generated from a single renormalizable Yukawa interaction, while the lighter masses and the mixing angles are generated by non-renormalizable operators of the grand unified theory. The hierarchy of masses and mixing angles is thereby related to the ratio of grand to Planck scales, $M_G / M_P$. An explicit realization of the origin of such an economical pattern of operators is given in terms of a set of spontaneously broken family symmetries. In the preferred models the top quark is found to be heavy: $M_t = 180 \pm 15$ GeV, and $\tan \beta$ is predicted to be very large. Predictions are also given for $m_s, m_s/m_d , m_u/m_d, V_{cb}, V_{ub}/V_{cb}$ and the amount of CP violation. Stringent tests of these theories will be achieved by more precise measurements of $M_t, V_{cb}, \alpha_s$ and $ V_{ub}/V_{cb}$ and by measurements of CP violation in neutral B meson decays.

Top quark condensation from broken family symmetry

We investigate the vacuum alignment in a fully dynamical “moose” model which breaks electroweak symmetry with a top quark condensate and show how the prefered vacuum depends on the explicit masses of the fermions involved. Our results are also applicable to the cases in which electroweak symmetry is broken by a fourth family of quarks, or by a technicolour mechanism. Such moose models allow the scale of new physics, Λ, to be in the TeV range with the absence of flavour changing neutral currents ensured by a GIM mechanism.

Goldstone bosons versus domain walls bounded by cosmic strings

It is shown that two possible schemes of string bounded domain wall formation are closely related. Walls can be avoided if a certain type of couplings between scalars, responsible for string and wall formation, is excluded from the potential. This enlarges the continous global symmetry of the model which, being broken, instead of domain walls gives rise to global strings and Gold-stone bosons. A realistic example of spontaneously broken family symmetry is considered. It is shown that the existence of the axion in the model with local chiral flavour symmetry SU(3)H can solve the domain wall problem.

Superconducting cosmic strings in models with spontaneously broken family symmetry

It is shown that superconducting cosmic strings with some specific properties naturally exist in models of spontaneously broken family symmetry. Superconductivity may be of both types - bosonic and fermionic. There exists a possible mechanism of string conservation.