Email: salexand@haverford.edu
Phone: 610-896-2973
Office: KINSC L106

Research

Cosmology and Fundamental Physics

The research of Dr. Stephon Alexander primarily focuses on

  1. Understanding the nature of dark energy in the universe.
  2. Understanding the origin of matter over anti-matter (baryogenesis). in the universe.
  3. Understanding the origin of large scale structure in the universe from fundamental theory.
  4. How are space-time singularities, like the initial big-bang singularity resolved?
  5. How do we test a theory of quantum gravity with observations in cosmology?
  6. What is the origin of neutrino masses; how may this be connected to cosmology?

Current data from Type Ia supernovae and the WMAP data all point to a universe dominated by a negative pressure fluid dubbed "dark energy". This dark energy is connected to the cosmological constant problem. Stated simply, the cosmological constant may have contributions from vacuum fluctuations of all quantum fields, or it may arise purely from geometry. There is an embarassing discrepancy between the precision theoretical evaluation of the vacuum energy and the observed value of dark energy. My research addresses the dark energy problem at the the level of quantum gravity and particle physics. Currently, I am developing a framework to explain the dark energy problem interms a quantum gravitational fermionic condensation mechanism that is intrinsically tied to the origin of parity violation the the electroweak interactions.

While collider physics has firmly established the equality between matter and antimatter, we observe mostly matter on astrophysical and cosmological scales. Indeed the precise balance between the matter and antimatter asymmetry is neccessary for the formation of light elements in galaxies. It still remains a mystery as to how this baryon asymmetry arose in the early universe. My research addresses baryogenesis as a result of gravitational waves that were present during the inflationary epoch. With colleagues in the Penn State Astronomy & Astrophysics department, we are developing this model for a possible direct detection in the upcoming LISA gravitational wave detector.

On scales over 100 megaparsecs, our universe is homogenous and isotropic. However, at smaller distances we oberve a plethora of dramatic structure, such as galaxies and clusters of galaxies.  My reserach involves finding a causal physical mechanism to explain fundamentally how structure in the universe was formed in the early stages of the universe's expansion. Cosmic inflation is a successful model which predicts that the origin of this large scale structure emerged from primordial quantum fluctuations of a scalar field. However, this paradigm suffers from conceptual and technical issues. In focussing on these issues, I am improving on the problems which plague inflation by building more realistic models.