High Energy Physics

The  QCD axion is a curious Dark Matter candidate, having a mass like the neutrino, but behaving as Cold Dark Matter. I will review how this occurs, and discuss the interesting question  of whether WIMPs could be distinguished from axions with Large Scale Structure data.

Similarly to the probability distribution of energy in physics, the probability distribution of money among the agents in a closed economic system is also expected to follow the exponential Boltzmann-Gibbs law, as a consequence of entropy maximization.  Analysis of empirical data shows that income distributions in the USA, European Union, and other countries exhibit a well-defined two-class structure.  The majority of the population (about 97%) belongs to the lower class characterized by the exponential ("thermal") distribution.  The upper class (about 3% of the population) is characterized by the Pareto power-law ("superthermal") distribution, and its share of the total income expands and contracts dramatically during booms and busts in financial markets.  Globally, data analysis of energy consumption per capita around the world shows decreasing inequality in the last 30 years and convergence toward the exponential probability distribution, in agreement with the maximal entropy principle. Similar results are found for the global probability distribution of CO2 emissions per capita.  All papers are available at http://physics.umd.edu/~yakovenk/econophysics/.  For recent coverage in Science magazine, see http://www.sciencemag.org/content/344/6186/828

I will propose a proof for a monotonicity theorem, or c-theorem, for a three-dimensional Conformal Field Theory (CFT) on a space with a boundary, and for a two-dimensional defect coupled to a higher-dimensional CFT. The proof is applicable only to renormalization group flows that are localized at the boundary or defect, such that the bulk theory remains conformal along the flow, and that preserve locality, reflection positivity, and Euclidean invariance along the defect. The method of proof is a generalization of Komargodski’s proof of Zamolodchikov’s c-theorem. The key ingredient is an external “dilaton” field introduced to match Weyl anomalies between the ultra-violet (UV) and infra-red (IR) fixed points. Reflection positivity in the dilaton’s effective action guarantees that a certain coefficient in the boundary/defect Weyl anomaly must take a value in the UV that is larger than (or equal to) the value in the IR. This boundary/defect c-theorem may have important implications for many theoretical and experimental systems, ranging from graphene to branes in string theory and M-theory.

Identifying the nature of dark  matter is one of the most challenging problems in physics. There is a general consensus that dark matter is a weakly interacting particle and predominantly cold, yet the Cold Dark Matter (CDM) hypothesis remains to be verified.  I will show that next cosmological surveys could play a leading role in understanding the dark matter microphysics.