String Phenomenology: Past, Present and Future Perspectives

Abstract

The observation of a scalar resonance at the LHC, compatible with perturbative electroweak symmetry breaking, reinforces the Standard Model parameterisation of all subatomic data. The logarithmic evolution of the SM gauge and matter parameters suggests that this parameterisation remains viable up to the Planck scale, where gravitational effects are of comparable strength. String theory provides a perturbatively consistent scheme to explore how the parameters of the Standard Model may be determined from a theory of quantum gravity. The free fermionic heterotic string models provide concrete examples of exact string solutions that reproduce the spectrum of the Minimal Supersymmetric Standard Model. Contemporary studies entail the development of methods to classify large classes of models. This led to the discovery of exophobic heterotic-string vacua and the observation of spinor-vector duality, which provides an insight to the global structure of the space of (2,0) heterotic-string vacua. Future directions entail the study of the role of the massive string states in these models and their incorporation in cosmological scenarios. A complementary direction is the formulation of quantum gravity from the principle of manifest phase space duality and the equivalence postulate of quantum mechanics, which suggest that space is compact. The compactness of space, which implies intrinsic regularisation, may be tightly related to the intrinsic finite length scale, implied by string phenomenology.

Hierarchy spectrum of SM fermions: from top quark to electron neutrino

“…In literature the most of effort based on phenomenological models assuming a particular texture in the original fermion-mass matrices in quark and/or lepton sectors to find the fermion-family mixing matrices as functions of observed fermion masses, i.e., the eigenvalues of the original fermion-mass matrices. Whereas some other models try to find the relations of fermion masses and familymixing matrices on the basis of theoretically model-building approaches, for example, the left-right symmetric scenario [5]- [9] and [16,42], string theory phenomenology [43,44] or the scenario of effective vector-like W ± -coupling at high energies [25,26]. In the model-independent approach, the fermion-mass matrices with different null matrix elements (texture zeros) are considered to find the relations of fermion mass and mixing patterns [45]- [50].…”