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Series

2004

Physics Department Faculty Publication Series

Articles 1 - 13 of 13

Full-Text Articles in Physics

Parallel Dynamics And Computational Complexity Of Network Growth Models, Benjamin Machta, Jonathan Machta Aug 2004

Parallel Dynamics And Computational Complexity Of Network Growth Models, Benjamin Machta, Jonathan Machta

Physics Department Faculty Publication Series

No abstract provided.


Long Distance Chiral Corrections In Beta Meson Amplitudes, Jj Sanz-Cillero, Jf Donoghue, A Ross Jan 2004

Long Distance Chiral Corrections In Beta Meson Amplitudes, Jj Sanz-Cillero, Jf Donoghue, A Ross

Physics Department Faculty Publication Series

We discuss the chiral corrections to fB and BB with particular emphasis on determining the portion of the correction that arises from long distance physics. For very small pion and kaon masses all of the usual corrections are truly long distance, while for larger masses the long distance portion decreases. These chiral corrections have been used to extrapolate lattice calculations towards the physical region of lighter masses. We show in particular that the chiral extrapolation is better behaved if only the long distance portion of the correction is used. We also display the long distance portions of the infrared enhanced …


Commensurate Two-Component Bosons In An Optical Lattice: Ground State Phase Diagram, A Kuklov, N Prokof'ev, B Svistunov Jan 2004

Commensurate Two-Component Bosons In An Optical Lattice: Ground State Phase Diagram, A Kuklov, N Prokof'ev, B Svistunov

Physics Department Faculty Publication Series

Two sorts of bosons in an optical lattice at commensurate filling factors can form five stable superfluid and insulating ground states with rich and nontrivial phase diagram. The structure of the ground state diagram is established by mapping a d-dimensional quantum system onto a (d+1)-dimensional classical loop-current model and Monte Carlo (MC) simulations of the latter. Surprisingly, the quantum phase diagram features, besides second-order lines, first-order transitions and two multicritical points. We explain why first-order transitions are generic for models with pairing interactions using microscopic and mean-field (MF) arguments. In some cases, the MC results strongly deviate from the MF …


Truncated-Determinant Diagrammatic Monte Carlo For Fermions With Contact Interaction, E Bourovski, Nikolai Prokof'ev, Boris Svistunov Jan 2004

Truncated-Determinant Diagrammatic Monte Carlo For Fermions With Contact Interaction, E Bourovski, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

For some models of interacting fermions the known solution to the notorious sign problem in Monte Carlo (MC) simulations is to work with macroscopic fermionic determinants; the price, however, is a macroscopic scaling of the numerical effort spent on elementary local updates. We find that the ratio of two macroscopic determinants can be found with any desired accuracy by considering truncated (local in space and time) matices. In this respect, MC for interacting fermionic systems becomes similar to that for the sign-problem-free bosonic systems with system-size independent update cost. We demonstrate the utility of the truncated-determinant method by simulating the …


Superfluid-Superfluid Phase Transitions In A Two-Component Bose-Einstein Condensate, A Kuklov, Nikolai Prokof'ev, Boris Svistunov Jan 2004

Superfluid-Superfluid Phase Transitions In A Two-Component Bose-Einstein Condensate, A Kuklov, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

Depending on the Hamiltonian parameters, two-component bosons in an optical lattice can form at least three different superfluid phases in which both components participate in the superflow: a (strongly interacting) mixture of two miscible superfluids (2SF), a paired superfluid (PSF) vacuum, and (at a commensurate total filling factor) the super-counter-fluid (SCF) state. We study the universal properties of the 2SF-PSF and 2SF-SCF quantum phase transitions and show that (i) they can be mapped onto each other and (ii) their universality class is identical to the (d+1)-dimensional normal-superfluid transition in a single-component liquid. The finite-temperature 2SF-PSF(SCF) transitions and the topological properties …


Conserved Gravitational Charges From Yano Tensors, David Kastor, Jennie Traschen Jan 2004

Conserved Gravitational Charges From Yano Tensors, David Kastor, Jennie Traschen

Physics Department Faculty Publication Series

The defining properties of Yano tensors naturally generalize those of Killing vectors to anti-symmetric tensor fields of arbitrary rank. We show how the Yano tensors of flat spacetime can be used to construct new, conserved gravitational charges for transverse asymptotically flat spacetimes. The relationship of these new charges to Yano tensors parallels that of ordinary ADM conserved charges to Killing vectors. Hence, we call them Y-ADM charges. A rank n Y-ADM charge is given by an integral over a co-dimension n slice of spatial infinity. In particular, a rank (p+1) Y-ADM charge in a p-brane spacetime is given by an …


Truncated-Determinant Diagrammatic Monte Carlo For Fermions With Contact Interaction, E Bourovski, Nikolai Prokof'ev, Boris Svistunov Jan 2004

Truncated-Determinant Diagrammatic Monte Carlo For Fermions With Contact Interaction, E Bourovski, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

For some models of interacting fermions the known solution to the notorious sign problem in Monte Carlo (MC) simulations is to work with macroscopic fermionic determinants; the price, however, is a macroscopic scaling of the numerical effort spent on elementary local updates. We find that the ratio of two macroscopic determinants can be found with any desired accuracy by considering truncated (local in space and time) matices. In this respect, MC for interacting fermionic systems becomes similar to that for the sign-problem-free bosonic systems with system-size independent update cost. We demonstrate the utility of the truncated-determinant method by simulating the …


Hole Digging In Ensembles Of Tunneling Molecular Magnets, I Tupitsyn, P Stamp, N Prokof'ev Jan 2004

Hole Digging In Ensembles Of Tunneling Molecular Magnets, I Tupitsyn, P Stamp, N Prokof'ev

Physics Department Faculty Publication Series

The nuclear spin-mediated quantum relaxation of ensembles of tunneling magnetic molecules causes a “hole” to appear in the distribution of internal fields in the system. The form of this hole and its time evolution, are studied using Monte Carlo simulations. It is shown that the line shape of the tunneling hole in a partially depolarized sample must have a Lorentzian line shape. The short-time half-width ξo in Fe8 crystals should be ∼E0, the half-width of the nuclear spin multiplet, but this result is not generally true. The Lorentzian hole line shape and the short-time √t relaxation in weakly polarized samples …


Weakly Interacting Bose Gas In The Vicinity Of The Critical Point, Nikolai Prokof'ev, O Ruebenacker, Boris Svistunov Jan 2004

Weakly Interacting Bose Gas In The Vicinity Of The Critical Point, Nikolai Prokof'ev, O Ruebenacker, Boris Svistunov

Physics Department Faculty Publication Series

We consider a three-dimensional weakly interacting Bose gas in the fluctuation region (and its vicinity) of the normal-superfluid phase transition point. We establish relations between basic thermodynamic functions: density, n(T, ì), superfluid density ns(T, ì), and condensate density, ncnd(T, ì). Being universal for all weakly interacting |ø|4 systems, these relations are obtained from Monte Carlo simulations of the classical |ø|4 model on a lattice. Comparing with the mean-field results yields a quantitative estimate of the fluctuation region size. Away from the fluctuation region, on the superfluid side, all the data perfectly agree with the predictions of the quasicondensate mean field …


Superfluid-Insulator Transition In Commensurate Disordered Bosonic Systems: Large-Scale Worm Algorithm Simulations, Nikolai Prokof'ev, Boris Svistunov Jan 2004

Superfluid-Insulator Transition In Commensurate Disordered Bosonic Systems: Large-Scale Worm Algorithm Simulations, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

We report results of large-scale Monte Carlo simulations of superfluid-insulator transitions in disordered commensurate 2D bosonic systems. In the off-diagonal disorder case, we find that the transition is to a gapless incompressible insulator, and its dynamical critical exponent is z=1.5(2). In the diagonal-disorder case, we prove the conjecture that rare statistical fluctuations are inseparable from critical fluctuations on the largest scales and ultimately result in crossover to the generic universality class (apparently with z=2). However, even at strong disorder, the universal behavior sets in only at very large space-time distances. This explains why previous studies of smaller clusters mimicked a …


Detecting Supercounterfluidity By Ramsey Spectroscopy, A Kuklov, Nikolai Prokof'ev, Boris Svistunov Jan 2004

Detecting Supercounterfluidity By Ramsey Spectroscopy, A Kuklov, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

A two-component system of ultracold atoms in an optical lattice at integer total filling factor and strong enough onsite repulsion can form a supercounterfluid (SCF) phase, which can be viewed as the Bose-Einstein condensate (BEC) of pairs formed by particles of one sort and holes of another sort. In this quasimolecular BEC, no single-component BEC exists, and the net atomic flow is prohibited. We show that, in the case of the interconvertible species (like hyperfine states of Rb), the corresponding order parameter can be detected by spatially selective Ramsey spectroscopy. The method can be used, in particular, for revealing a …


Kelvin-Wave Cascade And Decay Of Superfluid Turbulence, E Kozik, Boris Svistunov Jan 2004

Kelvin-Wave Cascade And Decay Of Superfluid Turbulence, E Kozik, Boris Svistunov

Physics Department Faculty Publication Series

Kelvin waves (kelvons), the distortion waves on vortex lines, play a key part in the relaxation of superfluid turbulence at low temperatures. We present a weak-turbulence theory of kelvons. We show that nontrivial kinetics arises only beyond the local-induction approximation and is governed by three-kelvon collisions; a corresponding kinetic equation is derived. We prove the existence of Kolmogorov cascade and find its spectrum. The qualitative analysis is corroborated by numeric study of the kinetic equation. The application of the results to the theory of superfluid turbulence is discussed.


A Derivative Of The Gerasimov-Drell-Hearn Sum Rule, V Pascalutsa, Br Holstein, M Vanderhaeghen Jan 2004

A Derivative Of The Gerasimov-Drell-Hearn Sum Rule, V Pascalutsa, Br Holstein, M Vanderhaeghen

Physics Department Faculty Publication Series

We derive a sum rule which establishes a linear relation between a particle's anomalous magnetic moment and a quantity connected to the photoabsorption cross section. This quantity cannot be measured directly. However, it can be computed within a given theory. As an example, we demonstrate validity of the sum rule in QED at tree level—the renowned Schwinger's correction to the anomalous magnetic moment is readily reproduced. In the case of the strong interactions, we also consider the calculation of the nucleon magnetic moment within chiral theories.