High energy physics and cosmology at the unification frontier: Opportunities and challenges in the coming years

Abstract

We give here an overview of recent developments in high energy physics and cosmology and their interconnections that relate to unification, and discuss prospects for the future. Thus there are currently three empirical data that point to supersymmetry as an underlying symmetry of particle physics: the unification of gauge couplings within supersymmetry, the fact that nature respects the supersymmetry prediction that the Higgs boson mass lie below 130 GeV, and vacuum stability up to the Planck scale with a Higgs boson mass at [Formula: see text][Formula: see text]125 GeV while the Standard Model does not do that. Coupled with the fact that supersymmetry solves the big hierarchy problem related to the quadratic divergence to the Higgs boson mass square along with the fact that there is no alternative paradigm that allows us to extrapolate physics from the electroweak scale to the grand unification scale consistent with experiment, supersymmetry remains a compelling framework for new physics beyond the Standard Model. The large loop correction to the Higgs boson mass in supersymmetry to lift the tree mass to the experimentally observable value, indicates a larger value of the scale of weak scale supersymmetry, making the observation of sparticles more challenging but still within reach at the LHC for the lightest ones. Recent analyses show that a high energy LHC (HE-LHC) operating at 27 TeV running at its optimal luminosity of [Formula: see text] can reduce the discovery period by several years relative to HL-LHC and significantly extend the reach in parameter space of models. In the coming years several experiments related to neutrino physics, searches for supersymmetry, on dark matter and dark energy will have direct impact on the unification frontier. Thus the discovery of sparticles will establish supersymmetry as a fundamental symmetry of nature and also lend direct support for strings. Further, discovery of sparticles associated with missing energy will constitute discovery of dark matter with LSP being the dark matter. On the cosmology front more accurate measurement of the equation of state, i.e. [Formula: see text], will shed light on the nature of dark energy. Specifically, [Formula: see text] will likely indicate the existence of a dynamical field, possibly quintessence, responsible for dark energy and [Formula: see text] would indicate an entirely new sector of physics. Further, more precise measurements of the ratio [Formula: see text] of tensor to scalar power spectrum, of the scalar and tensor spectral indices [Formula: see text] and [Formula: see text] and of non-Gaussianity will hopefully allow us to realize a Standard Model of inflation. These results will be a guide to further model building that incorporates unification of particle physics and cosmology.