Viable dark matter via radiative symmetry breaking in a Higgs portal extension of the standard model

Speaker: Zhi-Wei Wang
Location: Physics 175
Time: 3:30,  June 19 2014

Abstract: We consider generation of dark matter mass via radiative
electroweak symmetry breaking in an extension of the conformal Standard Model
containing a singlet scalar field with a Higgs portal interaction. Generating the mass
from a sequential process of radiative electroweak symmetry breaking followed by
a conventional Higgs mechanism can account for less than 30% of the cosmological
dark matter abundance. However in a dynamical approach where both Higgs and
scalar singlet masses are generated via radiative electroweak symmetry breaking we
obtain much higher levels of dark matter abundance: 10%-80% for a dark matter
mass of 80 GeV < Ms < 96 GeV when higher-order contributions are estimated.
The dynamical approach also predicts a small scalar-singlet self-coupling, providing
a natural explanation for the astrophysical observations that place upper bounds
on dark matter self-interaction. The predictions in both methods are within the
detection region of the next generation XENON experiment.

D(γ,n)H: Photodisintegration of the Deuteron at 18 MeV using Linearly Polarized Photons

Speaker: Glen Pridham
Location: Physics 175
Time: 3:30pm, June 12th, 2014

(Update) You can view the presentation here.

Abstract: The deuteron is probably the simplest nuclear system: it is composed of two (composite) particles and has only one bound state.  As such, it has long served as the first test case for new experimental and theoretical methods.  Although the deuteron is important on its own merit (e.g. for fusion), precision measurements and calculations also serve to enhance the accuracy of nucleon­nucleon potentials which, in turn, improve the accuracy of all nuclear calculations.

Despite its simplicity: deuteron photodisintegration has a history of inconsistent experimental results, which began being cleaned up in the late 1980s with the advent of monochromatic photon sources (i.e. free­ electron lasers and Compon laser scattering beams).  Concurrently, the use of retarded Green`s functions and realistic meson exchange potentials in modelling the nuclear force served to greatly enhance theoretical accuracy.  The pursuit of an experimental and theoretical consensus on deuteron photodisintegration continues to this day: gradually mapping out the energy landscape.

In this seminar, I will present the results of a deuteron photodisintegration experiment performed in October 2010 at the High­Intensity Gamma Source (HIγS) Free­Electron Laser (FEL) at Duke University in Durham, North Carolina.  These results are compared to a recent calculation by Schwamb and Arenhӧvel who used a one meson exchange nucleon­nucleon potential with delta baryon intermediate states, relativistic corrections, and retarded Green`s functions.

I will include an overview of the use of mesons as the effective quark degrees of freedom in the nuclear regime; which allows the nuclear force to be rigorously modelled as the exchange of virtual mesons.

Predicted novel crystal structures of Xe-Clx (x=1, 2 and 4) by ASAP and CALYPSO

Speaker: Niloofar Zarifi
Location: Physics 175
Time: 3:30,  June 4th, 2014

The presentation can be viewed here.

Abstract: Noble gases are elements with close shell configurations and not expected to form chemical bonding easily except with electronegative halogen atoms. Therefore, these halide compounds have attracted great attentions due to the importance for scientific interest. Here, we performed extensive structure searches on XeClx (x=1, 2 and 4) under high pressure using the GA and PSO methodology. Several novel crystal structures were uncovered for the first time at high pressures. Our calculations confirm existence of molecular Cl2 and Xe atoms in crystalline structures for XeCl. This compound remains an insulator up to 60GPa. The high pressure phase transition has been widely studied for XeCl2. Electronic calculations predicted their metallic property up to 80 GPa. For XeCl4 the metallic state exists at lower pressure.

Our results provide new understanding of novel crystalline structure of Xe compounds at high pressure.