On Observational Constraint Of Cosmological Phase Transitions With Astronomical Surveys

This thesis concerns the analysis of Cosmological Phase Transitions(CPTs)which provides an exciting possibility to probe physics of the early Universe.According to The Big Bang Theory(TBBT),the Universe underwent a series of breaking of funda-mental symmetries during CPT.Such phase transitions have various exciting cosmo-logical consequences and hence,provides a connection between particle physics and cosmology.As the Universe continued to cool down till T～300GeV,a spontaneous breakdown of Electroweak symmetry occurs.It allowed particles of standard model to gain gauge invariant masses.Although Electroweak Phase Transition(EWPT)of the Standard Model(SM)could be a crossover,yet various well-motivated extensions of the Standard Model are introduced.Such extensions reopen the possibility of new physics of a First-Order Phase Transition(FOPT)at the electroweak scale that would be capable of emitting significant amount of gravitational waves(GWs).Other CPTs,like a spontaneous symmetry breaking at Grand Unified Theories(GUT)scale,may give rise to topological defects.In particular,such relic flaws would provide observable signatures as they are characterized by their incredible amount of energy.Cosmic Strings(CSs)are one dimensional topological defects and could pro-vide insight into the physics of very early Universe.If they are Superconducting Cos-mic Strings(SCSs),they can decay by emitting electromagnetic radiations over short timescales.Thus,the transient radio bursts,called Fast Radio Bursts(FRBs),can be applied to test the huge amount of energy emitted from SCSs.This thesis comprises of four chapters.Chapter 1 briefly revisits the background study on cosmology and some funda-mentals of CPT.It focuses on the aftermath of CPT,such as GWs,CSs etc.Chapter 2 is devoted to the detailed analysis on the stochastic background of GWs induced by FOPT through the developed techniques of numerical simulations.To ex-plore new physics based on strong FOPTs,distinct SM extensions have been introduced.The singlet Majoron model is one of such extensions which was suggested to deal with the neutrino mass problem.In said model,we discuss CPTs for two-dimensional(2D)fields and investigate the resulting GWs.Firstly,we determine the tree-level effective potential of the doublet Higgs along with a singlet.We simulate the 2D)CPTs by im-plementing "CosmoTransitions" which is a publically available Python code.We verify and discuss the CPTs’ patterns discussed in the previous studies.We also investigate new CPT patterns,such as strong FOPTs tunneling between two vacua located on two distinct axis.The two-field phase space analysis is more elegant than a single-field ap-proximation as it suggests more valuable CPT patterns.We determine the gravitational waves(GWs)generated by FOPTs.Chapter 3 concerns the updated constraints on SCSs by considering progress in observational grounds in FRBs astronomy.Assuming strings follow an exponential dis-tribution characterized by current,we show that two parameters in our contexts,which are the characteristic tension(Gμ)and a parameter which describes the aforementioned exponential distribution(Ic),can be constrained by FRBs experiments.Particularly,we investigate data sets from Parkes and ASKAP.We scanned a parameter space where Gμ～[10-17,10-12]and Ic～[10-1,102]GeV,and concluded that Parkes jointly with ASKAP can constrain the parameter space for SCSs.Finally,Chapter 4 focuses on the summary and future perspectives relevant to the study discuss in this thesis.