• Spin Wave Feynman Diagram Vertex Computation Package

      Datta, Trinanjan; Price, Alexander; Javernick, Philip; Department of Chemistry and Physics; Department of Physics and Astronomy (2016-03)
      Spin wave theory is a well-established theoretical technique that can correctly predict the physical behavior of ordered magnetic states. However, computing the effects of an interacting spin wave theory incorporating magnons involve a laborious by hand derivation of Feynman diagram vertices. The process is tedious and time consuming. Hence, to improve productivity and have another means to check the analytical calculations, we have devised a Feynman Diagram Vertex Computation package. In this talk, we will describe our research group’s effort to implement a Mathematica based symbolic Feynman diagram vertex computation package that computes spin wave vertices. Utilizing the non-commutative algebra package NCAlgebra as an add-on to Mathematica, symbolic expressions for the Feynman diagram vertices of a Heisenberg quantum antiferromagnet are obtained. Our existing code reproduces the well-known expressions of a nearest neighbor square lattice Heisenberg model. We also discuss the case of a triangular lattice Heisenberg model where non collinear terms contribute to the vertex interactions.
    • Studying the Interplay between Superconductivity and Anti-Ferromag-Netism through Bose-Fermi Mixtures on Optical Lattices

      Brackett, Jeremy; Department of Chemistry and Physics (2016-03)
      Motivated by the recent experimental progress with ultra-cold atoms, we investigate the physics of a Bose-Fermi mixture on a two dimensional optical lattice. We treat the system parameters such that 2-component fermions are in a deep external trap and weakly interacting bosons are in a shallow external trap, however both of these atoms are subjected to the same optical lattice. In this parameter regime, the bosons form a Bose-Einstein condensate and mediate an attractive interaction between fermions through low energy Bose excitations. As a result, the dynamics of the fermions can be described by the single band Hubbard model that involves on-site repulsive interaction and elementary excitation mediated attractive interactions. Using a mean field theory, we derive an effective action up to the quartic order in both d-wave superconducting and anti-ferromagnetic order parameters. Using this Landau energy functional, we then discuss the phase transition and study the competition and/or cooperation of anti-ferromagnetism and d-wave superconductivity in the system.
    • Ufmylation Maintains the Proper Er Homeostasis of Pancreas from Alcoholic Rodents

      Miller, Camille; Department of Biological Sciences (2016-03)
      The accumulation of misfolded pancreatic enzymes in the rough ER causes an activation of unfolded protein response (UPR). Ufmylation (Ufm1) is a novel post-translational ubiquitin-like modification system involved in UPR. Ufm1 modifies its target proteins through a biochemical pathway that involves E3 ligase. RCAD is an E3 ligase that forms a complex with DDRGK1. Be- cause of the synthesis, folding/sorting of pancreatic enzymes takes place in the rough ER and Ufm1 is involved in ER homeostasis. The first objective was to study the importance of RCAD and DDRGK1 in both proper sorting and secretion of digestive enzymes. We found that the lack of RCAD or DDRGK1 causes an increase in the expression of pancreatic amylase and trypsin activation. Because Ufmylation is involved in rough ER homeostasis and alcoholism causes changes in the expression of multiple rough ER proteins involved in the UPR, the next objective was to compare the relative expression of RCAD and DDRGK1 in alcohol-treated rats with non-treated rats. We found that both RCAD and DDRGK1 are highly expressed in alcohol-treated pancreas. In conclusion, alcoholism could increase the level of these proteins in the exocrine pancreas to protect it from ER stress and inflammation. Funding Source: Center for Undergraduate Research and Scholarship, Department of Biological Sciences and Scholarly Activity Award