High Energy Theory

Theoretical High Energy Physics

THEP Homepage: http://home.phy.iitb.ac.in/~thep/

Elementary Particle physics and physics beyond the Standard Model

The Standard Model of elementary particles is an extremely successful theory of strong, weak and electromagnetic forces. The discovery of a Higgs-like boson is an important step towards a final confirmation of the Standard Model. Yet many open questions remain unanswered.

Origin of the Higgs boson: The Higgs boson plays an important role in the Standard Model and provides a universal mechanism for particle masses. Theoretically it is required as the remnant of electroweak symmetry breaking (EWSB) that separates the weak forces from electromagnetism. Is the 125 GeV boson discovered at the LHC really the Higgs boson of the Standard Model? If so, why is its mass much smaller than the naively expected theoretical value?

Top quark physics: Is there any connection of EWSB to the mass of the top quark? We have been exploring Higgs and Top quark physics in beyond Standard Model (bSM) models. We have especially been exploring collider signatures of new physics contributions to Higgs and top quark observables, through polarization and jet substructure studies both at the Large Hadron Collider (LHC) and the proposed International Linear Collider (ILC).

Understanding the proton spin: We know that the proton has spin 1/2. How is this built up from the intrinsic spin of quarks and gluons and their orbital angular momentum? In a high energy collider experiment, if one polarizes one or both beams either longitudinally or in the transverse direction, what new information can one obtain about the structure of the nucleons and their interaction?

Neutrino Physics: What makes the neutrino masses a trillion times smaller than the EWSB scale? What new physics underlies their individual masses and mixings? Is one or more neutrino its own antiparticle? What is the mass hierarchy of the neutrinos? Is there any CP violation in the neutrino sector?

Flavour Physics: Both quarks and the leptons appear with identical gauge couplings across three generations, this is associated with a "flavour'' identity that is preserved by the strong and electromagnetic interactions. This flavour identity is violated in charge- current weak interactions and it also leads to a mixing between generations. What explains the masses and mixings of the fermions in the Standard Model? What are the CP violating parameters in their interactions and what connection does this have to the baryon asymmetry of the universe?

Unified Theories

The explanation for some of the theoretical issues with elementary particles can be found by invoking new symmetry principles. Historically, this has been an extremely fruitful direction. In addition, we would like a theory of fundamental particles that includes quantum gravity.

Supersymmetric gauge theories: Supersymmetry is a theoretically appealing quantum symmetry, that relates bosons and fermions. The problems faced by the standard Higgs can be reduced if nature is supersymmetric at the weak scale. Additionally, if we assume that the unequal participation of left handed and right handed particles in the weak force is only a low energy manifestation, we can construct left