I am interested in understanding the fundamental laws of physics. Both particle physics and cosmology have recently celebrated the experimental confirmation of their respective "standard models".
In particle physics, ATLAS and CMS at CERN have discovered the Higgs boson, have measured its mass, and have begun to test the standard model predictions for its couplings. The Higgs discovery marked a milestone in our understanding of electroweak symmetry breaking, but it did not close the chapter on the Higgs or on the Standard Model. We still do not understand why there are three generations of quarks and leptons, why they have their peculiar pattern of masses and mixing, what makes up the Dark Matter and Dark Energy in the Universe, and why CP symmetry is violated only in the weak interactions. And even the Higgs field itself poses new questions because in the Standard Model the Higgs mass suffers from a quantum instability. Trying to cure this instability has motivated much of my work on Supersymmetry, Extra Dimensions and Little Higgs Theories. Recently, a new "relaxion" mechanism was proposed as a dynamical origin for the Higgs mass which could solve the quantum instability problem. I am constructing new models which implement the relaxion mechanism with the goal of finding a simpler model.
I maintain an interest in anomalies in data from the LHC or elsewhere. One such anomaly is an excess of diboson events seen in Run 1 of the LHC. With Cohen and current student Buen-Abad I studied a new model with a W' boson which decays to W and Z bosons and could explain this anomaly. The model also predicts a Z' resonance which should be within reach of the LHC in 2016. Another anomaly concerns the decays of B-mesons into final states with electron or muon pairs. The Standard Model predicts equal rates for these processes because of lepton universality. However recent LHCb data suggest otherwise (at about 3 sigma). I proposed models which might explain this data and suggested new observables which can be measured at the LHC to confirm or refute lepton universality.
In cosmology, measurements of the CMB, BAO, LSS, and H0 have established LambdaCDM as the Standard Model of cosmology. However, there are some recent inconsistencies in this picture which would - if they continue to hold up - force us to amend LCDM to account for new sources of energy or interactions in the Universe. Marques-Tavares, Buen-Abad, Lesgourgues and I proposed a new model for dark matter and dark radiation. We showed that our "non-Abelian dark matter" can relax the tension between the CMB measurements from Planck and WMAP and measurements of the expansion rate of the universe today (H0) and the distribution of matter on galaxy cluster scales (sigma_8). We are currently checking the consistency of our model with other cosmological data.
Current and former graduate students:
- Manuel Buen-Abad
- Gustavo Marques-Tavares (now postdoc at Stanford) , old news about Gustavo's LHC-TI award.
- Tuhin Roy (now faculty at Tata Institute)