Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session J14: Computational Methods in Particle & Nuclear Physics |
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Sponsoring Units: DCOMP DPF DNP Chair: Dean Lee, North Carolina State University Room: Grand Hall East C |
Sunday, April 1, 2012 1:30PM - 1:42PM |
J14.00001: Novel phase in SU(3) lattice gauge theories with many light fermions David Schaich, Anqi Cheng, Anna Hasenfratz, Gregory Petropoulos Our ongoing lattice studies of SU(3) gauge theories with $N_f=8$ and 12 fundamental fermions recently resulted in the observation of unexpected phase structures. For small fermion masses, both systems possess two distinct transitions at finite temperature. The $N_f=12$ finite-temperature transitions converge to two well-separated bulk phase transitions at zero temperature, consistent with an IR-conformal phase at weak coupling. Preliminary studies suggest that similar convergence to bulk transitions occurs for $N_f=8$. For both systems, the novel phase between the two transitions is confining but has a very small, possibly vanishing, chiral condensate. The meson spectrum also shows unusual properties in this phase. Our results appear consistent with a scenario in which this phase is chirally broken by a higher-order (four-fermion) condensate. [Preview Abstract] |
Sunday, April 1, 2012 1:42PM - 1:54PM |
J14.00002: Large N QCD with adjoint fermions Rajamani Narayanan Large N QCD with adjoint fermions is simulated on a single site lattice using overlap fermions. Reduction is invoked to study continuum infinite volume physics. A scale that identifies the transition from physical weak to strong coupling is precisely defined on the lattice. This scale is measured as a function of the lattice coupling and compared with perturbative running of the scale. The spectrum of the overlap Dirac operator is studied with the aim of measuring chiral symmetry breaking. [Preview Abstract] |
Sunday, April 1, 2012 1:54PM - 2:06PM |
J14.00003: Finite Lattice Size Corrections the Energy-Momentum Dispersion Zachary McDargh Lattice Gauge Theory (LGT) describes gauge and matter fields on a discrete Euclidian space-time lattice. Due to the finite spacing between the lattice points, there is a built-in ultra-violet energy cutoff. Additionally, there is an infrared energy cutoff in computer simulations due to the finite size of the lattice. With these approximations, the energy-momentum dispersion becomes modified. In this project, we study the recovery of the continuous energy-momentum dispersion. We perform fits of the correlation function from Markov Chain Monte Carlo (MCMC) simulations for various lattice sizes and spacings for a free-scalar field and for an Abelian $U(1)$ gauge field. For the scalar field, we also vary the mass of the particles; for $U(1)$ LGT, we vary the coupling constant $\beta$. These fits return the energy of a particle at definite momentum, from which the mass can be recovered using the energy-momentum dispersion. It is found that the finite-size effect in MCMC calculations decreases as $\exp(-N),$ where $N$ is the space dimension of the lattice. Furthermore, the effect is more significant for larger masses (scalar field) and coupling constant values near the phase transition $\beta_c=1.01$ ($U(1)$ LGT). [Preview Abstract] |
Sunday, April 1, 2012 2:06PM - 2:18PM |
J14.00004: Finite Size Scaling in Minimal Walking Technicolor Joel Giedt, Evan Weinberg We examine the finite size scaling hypothesis in the context of minimal walking technicolor. We find that quantities scale with an anomalous mass dimension that is too small for phenomenological purposes, but significantly different from zero. We discuss some of the systematic uncertainties in this analysis of the scaling hypothesis. [Preview Abstract] |
Sunday, April 1, 2012 2:18PM - 2:30PM |
J14.00005: Using FLUKA Monte Carlo transport code to develop parameterizations for fluence and energy deposition data for high-energy heavy charged particles John Brittingham, Lawrence Townsend, Janet Barzilla, Kerry Lee Monte Carlo codes provide an effective means of modeling three dimensional radiation transport; however, their use is both time- and resource-intensive. The creation of a lookup table or parameterization from Monte Carlo simulation allows users to perform calculations with Monte Carlo results without replicating lengthy calculations. FLUKA Monte Carlo transport code was used to develop lookup tables and parameterizations for data resulting from the penetration of layers of aluminum, polyethylene, and water with areal densities ranging from 0 to 100 g/cm2. Heavy charged ion radiation including ions from Z=1 to Z=26 and from 0.1 to 10 GeV/nucleon were simulated. Dose, dose equivalent, and fluence as a function of particle identity, energy, and scattering angle were examined at various depths. Calculations were compared to well-known data and the calculations of other deterministic and Monte Carlo codes. Results will be presented. [Preview Abstract] |
Sunday, April 1, 2012 2:30PM - 2:42PM |
J14.00006: Solving the many body pairing problem through Monte Carlo methods Mark Lingle, Alexander Volya Nuclear superconductivity is a central part of quantum many-body dynamics. In mesoscopic systems such as atomic nuclei, this phenomenon is influenced by shell effects, mean-field deformation, particle decay, and by other collective and chaotic components of nucleon motion. The ability to find an exact solution to these pairing correlations is of particular importance. In this presentation we develop and investigate the effectiveness of different methods of attacking the nucleon pairing problem in nuclei. In particular, we concentrate on the Monte Carlo approach. We review the configuration space Monte Carlo techniques, the Suzuki-Trotter breakup of the time evolution operator, and treatment of the pairing problem with non-constant matrix elements. The quasi-spin symmetry allows for a mapping of the pairing problem onto a problem of interacting spins which in turn can be solved using a Monte Carlo approach. The algorithms are investigated for convergence to the true ground state of model systems and calculated ground state energies are compared to those found by an exact diagonalization method. The possibility to include other non-pairing interaction components of the Hamiltonian is also investigated. [Preview Abstract] |
Sunday, April 1, 2012 2:42PM - 2:54PM |
J14.00007: Fermion bag solutions to some unsolved sign problems Anyi Li, Shailesh Chandrasekharan Some interesting lattice four-fermion models containing N flavors of staggered fermions with Z2 and U(1) chiral symmetries suffer from sign problems in the auxiliary field approach. Earlier calculations have either ignored these sign problems or have circumvented them by adding conjugate fermion fields which changes the model. In this talk we show that the recently proposed fermion bag approach solves these sign problems. The basic idea of the new approach is to collect unpaired fermionic degrees of freedom inside a fermion bag. A resummation of all fermion world lines inside the bag is then sufficient to solve the sign problems. The fermion bag approach provides new opportunities to solve in these ``unsolved'' four-fermion models in the chiral limit efficiently. [Preview Abstract] |
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