Phenomenological aspects of modular symmetry on neutrino mass models

Abstract

Standard model although has addressed and being successful regarding the fundamental particles newlineand their interactions, but, is deficient in explaining certain experimental evidences. In support newlineof the above statement, the list of things that standard model is sloppy about are dark matter, newlinedark energy, baryon asymmetry of the Universe, massive neutrinos, strong CP problem. This becomes the newlinedrive for everybody contributing in this field to find some answers either theoretically or experimentally. newlineHence, in this thesis, we have made an attempt to address certain issues, left open, by the help of various newlineprominent models. newlineSo, to start with, we present a model, where we have included A4 discrete symmetry in order to leap newlinebeyond the standard model (BSM). BSM physics helps us to accommodate right handed (RH) neutrinos newlinewhich is successful in explaining the tiny neutrino mass via seesaw mechanism. Therefore, we take the newlineadvantage of linear seesaw which demands the inclusion of left handed (LH) neutrinos too. In the model newlinewe have also introduced modular symmetry due to which Yukawa couplings implicitly depends on modulus newline¿ and explicitly on the dedekind eta function. Modular symmetry helps us in two aspects, one, reduces the newlineusage of flavon fields, which otherwise would make the model complicated and less predictive. Second, newlinemodular weights helps us to avoid unwanted Lagrangian terms to an extend. However, a global symmetry newlinei.e. U(1)X is included to avoid certain other Lagrangian terms which modular symmetry couldn t. All these newlinegimmick leads to the specific structure of linear seesaw mass matrix, which after diagonalisation gives newlineresults in accordance with current neutrino oscillation data i.e. at 3¾ level. This includes the reactor mixing newlineangle i.e. sin2 µ13, mass sum of the active neutrinos newlineP newlinemi which is well below the cosmological bound of newline0.12 eV. Other parameters like sin2 µ12 and sin2 µ23 are also well within the 3¾ limits. Introduction of right newlinehanded neutrinos, gave an idea that explanation of baryon asymmetry