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Full-Text Articles in Physics
The Renormalization Of The Energy-Momentum Tensor For An Effective Initial State, Hael Collins, R. Holman
The Renormalization Of The Energy-Momentum Tensor For An Effective Initial State, Hael Collins, R. Holman
Physics Department Faculty Publication Series
An effective description of an initial state is a method for representing the signatures of new physics in the short-distance structure of a quantum state. The expectation value of the energy-momentum tensor for a field in such a state contains new divergences that arise when summing over this new structure. These divergences occur only at the initial time at which the state is defined and therefore can be cancelled by including a set of purely geometric counterterms that also are confined to this initial surface. We describe this gravitational renormalization of the divergences in the energy-momentum tensor for a free …
Spin Diffusion In Trapped Gases: Anisotropy In Dipole And Quadrupole Modes, Wj Mullin, Rj Ragan
Spin Diffusion In Trapped Gases: Anisotropy In Dipole And Quadrupole Modes, Wj Mullin, Rj Ragan
Physics Department Faculty Publication Series
Recent experiments in a mixture of two hyperfine states of trapped Bose gases show behavior analogous to a spin-1/2 system, including transverse spin waves and other familiar Leggett-Rice-type effects. We have derived the kinetic equations applicable to these systems, including the spin dependence of interparticle interactions in the collision integral, and have solved for spin-wave frequencies and longitudinal and transverse diffusion constants in the Boltzmann limit. We find that, while the transverse and longitudinal collision times for trapped Fermi gases are identical, the Bose gas shows unusual diffusion anisotropy in both dipole and quadrupole modes. Moreover, the lack of spin …
Nuclear Central Force In The Chiral Limit, Jf Donoghue
Nuclear Central Force In The Chiral Limit, Jf Donoghue
Physics Department Faculty Publication Series
Chiral perturbation theory supplemented by the Omnes function is employed to study the strength of the isoscalar central nuclear interaction, GS, in the chiral limit vs the physical case. A very large modification is seen, i.e., ηs=GS chiral/GS physical=1.37±0.10. This large effect is seen to arise dominantly at low energy from the extra contributions made by massless pions at energies near the physical threshold where the physical spectral function must vanish kinematically. The slope away from the chiral limit, dS, is also calculated and is correspondingly large. I also explain why this large variation is to be expected.
Comment On “Hausdorff Dimension Of Critical Fluctuations In Abelian Gauge Theories”, N Prokof'ev, B Svistunov
Comment On “Hausdorff Dimension Of Critical Fluctuations In Abelian Gauge Theories”, N Prokof'ev, B Svistunov
Physics Department Faculty Publication Series
A Comment on the Letter by J. Hove, S. Mo, and A. Sudbø Phys. Rev. Lett. 85, 2368 (2000). The authors of the Letter offer a Reply.
The Fermi–Hubbard Model At Unitarity, F Bourovski, Nikolai Prokof'ev, Boris Svistunov, M Troyer
The Fermi–Hubbard Model At Unitarity, F Bourovski, Nikolai Prokof'ev, Boris Svistunov, M Troyer
Physics Department Faculty Publication Series
We simulate the dilute attractive Fermi–Hubbard model in the unitarity regime using a diagrammatic determinant Monte Carlo (MC) algorithm with worm-type updates. We obtain the dependence of the critical temperature on the filling factor ν and, by extrapolating to ν → 0, determine the universal critical temperature of the continuum unitary Fermi gas in units of Fermi energy: Tc/εF = 0.152(7). We also determine the thermodynamic functions and show how the MC results can be used for accurate thermometry of a trapped unitary gas.
Effects Of Finite Temperature On The Mott-Insulator State, G Pupillo, C Williams, Nikolai Prokof'ev
Effects Of Finite Temperature On The Mott-Insulator State, G Pupillo, C Williams, Nikolai Prokof'ev
Physics Department Faculty Publication Series
We investigate the effects of finite temperature on ultracold Bose atoms confined in an optical lattice plus a parabolic potential in the Mott-insulator state. In particular, we analyze the temperature dependence of the density distribution of atomic pairs in the lattice, by means of exact Monte Carlo simulations. We introduce a simple model that quantitatively accounts for the computed pair density distributions at low enough temperatures. We suggest that the temperature dependence of the atomic pair statistics may be used to estimate the system’s temperature at energies of the order of the atoms’ interaction energy.
Deconfined Criticality, Runaway Flow In The Two-Component Scalar Electrodynamics And Weak First-Order Superfluid-Solid Transitions, A Kuklov, Nikolai Prokof'ev, Boris Svistunov, M Troyer
Deconfined Criticality, Runaway Flow In The Two-Component Scalar Electrodynamics And Weak First-Order Superfluid-Solid Transitions, A Kuklov, Nikolai Prokof'ev, Boris Svistunov, M Troyer
Physics Department Faculty Publication Series
We perform a comparative Monte Carlo study of the easy-plane deconfined critical point (DCP) action and its short-range counterpart to reveal close similarities between the two models for intermediate and strong coupling regimes. For weak coupling, the structure of the phase diagram depends on the interaction range: while the short-range model features a tricritical point and a continuous U(1) × U(1) transition, the long-range DCP action is characterized by the runaway renormalization flow of coupling into a first (I) order phase transition. We develop a “numerical flowgram” method for high precision studies of the runaway effect, weakly I-order transitions, and …
Stresses And Strains In The First Law For Kaluza-Klein Black Holes, David Kastor, Jennie Traschen
Stresses And Strains In The First Law For Kaluza-Klein Black Holes, David Kastor, Jennie Traschen
Physics Department Faculty Publication Series
We consider how variations in the moduli of the compactification manifold contribute `pdV' type work terms to the first law for Kaluza-Klein black holes. We give a new proof for the S1 case, based on Hamiltonian methods, which demonstrates that the result holds for arbitrary perturbations around a static black hole background. We further apply these methods to derive the first law for black holes in 2-torus compactifications, where there are three real moduli. We find that the result can be simply stated in terms of constructs familiar from the physics of elastic materials, the stress and strain tensors. The …
On Black Strings & Branes In Lovelock Gravity, David Kastor, Robert Mann
On Black Strings & Branes In Lovelock Gravity, David Kastor, Robert Mann
Physics Department Faculty Publication Series
It is well known that black strings and branes may be constructed in pure Einstein gravity simply by adding flat directions to a vacuum black hole solution. A similar construction holds in the presence of a cosmological constant. While these constructions fail in general Lovelock theories, we show that they carry over straightforwardly within a class of Lovelock gravity theories that have (locally) unique constant curvature vacua.
Evolution Of Additional (Hidden) Quantum Variables In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe
Evolution Of Additional (Hidden) Quantum Variables In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe
Physics Department Faculty Publication Series
Additional variables (also often called “hidden variables”) are sometimes added to standard quantum mechanics in order to remove its indeterminism or “incompleteness” and to make the measurement process look more classical. Here we discuss a case in which an additional variable arises almost spontaneously from the quantum formalism: the emergence of a relative phase between two highly populated Fock-state Bose-Einstein condensates. The model simulated here involves the interference of two Bose condensates, one with all up spins and the other with down spins, along a z axis. With the clouds overlapping, we consider the results of measuring spins in a …
Fate Of Vacancy-Induced Supersolidity In 4he, M Boninsegni, A Kuklov, L Pollet, Nikolai Prokof'ev, Boris Svistunov, M Troyer
Fate Of Vacancy-Induced Supersolidity In 4he, M Boninsegni, A Kuklov, L Pollet, Nikolai Prokof'ev, Boris Svistunov, M Troyer
Physics Department Faculty Publication Series
The supersolid state of matter, exhibiting nondissipative flow in solids, has been elusive for 35 years. The recent discovery of a nonclassical moment of inertia in solid 4He by Kim and Chan provided the first experimental evidence, although the interpretation in terms of supersolidity of the ideal crystal phase remains a subject to debate. Using quantum Monte Carlo methods we investigate the long-standing question of vacancy-induced superflow and find that vacancies in a 4He crystal phase separate instead of forming a supersolid. On the other hand, nonequilibrium vacancies relaxing on defects of polycrystalline samples could provide an explanation for the …
Theory Of Cooling By Flow Through Narrow Pores, Wj Mullin, N Kalechofsky
Theory Of Cooling By Flow Through Narrow Pores, Wj Mullin, N Kalechofsky
Physics Department Faculty Publication Series
We consider the possibility of adding a stage to a dilution refrigerator to provide additional cooling by “filtering out” hot atoms. Three methods are considered: (1) effusion, where holes having diameters larger than a mean-free path allow atoms to pass through easily; (2) particle waveguidelike motion using very narrow channels that greatly restrict the quantum states of the atoms in a channel; (3) wall-limited diffusion through channels, in which the wall scattering is disordered so that local density equilibrium is established in a channel. We assume that channel dimensions are smaller than the mean-free path for atom-atom interactions. The particle …
Sigma Exchange In The Nuclear Force And Effective Field Theory, Jf Donoghue
Sigma Exchange In The Nuclear Force And Effective Field Theory, Jf Donoghue
Physics Department Faculty Publication Series
In the phenomenological description of the nuclear interaction an important role is traditionally played by the exchange of a scalar I=0 meson, the sigma, of mass 500–600 MeV, which however is not seen clearly in the particle spectrum and which has a very ambiguous status in QCD. I show that a remarkably simple and reasonably controlled combination of ingredients can reproduce the features of this part of the nuclear force. The use of chiral perturbation theory calculations for two pion exchange supplemented by the Omnes function for pion rescattering suffices to reproduce the magnitude and shape of the exchange of …
Quark And Lepton Masses And Mixing In The Landscape, Jf Donoghue, K Dutta, A Ross
Quark And Lepton Masses And Mixing In The Landscape, Jf Donoghue, K Dutta, A Ross
Physics Department Faculty Publication Series
Even if quark and lepton masses are not uniquely predicted by the fundamental theory, as may be the case in the string theory landscape, nevertheless their pattern may reveal features of the underlying theory. We use statistical techniques to show that the observed masses appear to be representative of a scale-invariant distribution, ρ(m)∼1/m. If we extend this distribution to include all the Yukawa couplings, we show that the resulting Cabibbo-Kobayashi-Maskawa matrix elements typically show a hierarchical pattern similar to observations. The Jarlskog invariant measuring the amount of CP violation is also well reproduced in magnitude. We also apply this framework …
Numerical Study Of The Three-Dimensional Random-Field Ising Model At Zero And Positive Temperature, Y Wu, Jonathan Machta
Numerical Study Of The Three-Dimensional Random-Field Ising Model At Zero And Positive Temperature, Y Wu, Jonathan Machta
Physics Department Faculty Publication Series
In this paper the three-dimensional random-field Ising model is studied at both zero temperature and positive temperature. Critical exponents are extracted at zero temperature by finite size scaling analysis of large discontinuities in the bond energy. The heat capacity exponent α is found to be near zero. The ground states are determined for a range of external field and disorder strength near the zero temperature critical point and the scaling of ground state tilings of the field-disorder plane is discussed. At positive temperature the specific heat and the susceptibility are obtained using the Wang-Landau algorithm. It is found that sharp …
Worm Algorithm For Continuous-Space Path Integral Monte Carlo Simulations, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Worm Algorithm For Continuous-Space Path Integral Monte Carlo Simulations, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Physics Department Faculty Publication Series
We present a new approach to path integral Monte Carlo (PIMC) simulations based on the worm algorithm, originally developed for lattice models and extended here to continuous-space many-body systems. The scheme allows for efficient computation of thermodynamic properties, including winding numbers and off-diagonal correlations, for systems of much greater size than that accessible to conventional PIMC simulations. As an illustrative application of the method, we simulate the superfluid transition of 4He in two dimensions.
Vortex-Phonon Interaction In The Kosterlitz-Thouless Theory, E Kozik, Nikolai Prokof'ev, Boris Svistunov
Vortex-Phonon Interaction In The Kosterlitz-Thouless Theory, E Kozik, Nikolai Prokof'ev, Boris Svistunov
Physics Department Faculty Publication Series
The “canonical” variables of the Kosterlitz-Thouless theory—fields Φ0(r) and φ(r), generally believed to stand for vortices and phonons (or their XY equivalents, like spin waves, etc.) turn out to be neither vortices and phonons, nor, strictly speaking, canonical variables. The latter fact explains paradoxes of (i) absence of interaction between Φ0 and φ, and (ii) nonphysical contribution of small vortex pairs to long-range phase correlations. We resolve the paradoxes by explicitly relating Φ0 and φ to canonical vortex-pair and phonon variables.
Superglass Phase Of 4he, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Superglass Phase Of 4he, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Physics Department Faculty Publication Series
We study different solid phases of 4He, by means of path integral Monte Carlo simulations based on a recently developed worm algorithm. Our study includes simulations that start off from a high-T gas phase, which is then “quenched” down to T=0.2 K. The low-T properties of the system crucially depend on the initial state. While an ideal hcp crystal is a clear-cut insulator, the disordered system freezes into a superglass, i.e., a metastable amorphous solid featuring off-diagonal long-range order and superfluidity.
Decoherence And Quantum Walks: Anomalous Diffusion And Ballistic Tails, Nikolai Prokof'ev, P.C.E Stamp
Decoherence And Quantum Walks: Anomalous Diffusion And Ballistic Tails, Nikolai Prokof'ev, P.C.E Stamp
Physics Department Faculty Publication Series
The common perception is that strong coupling to the environment will always render the evolution of the system density matrix quasiclassical (in fact, diffusive) in the long time limit. We present here a counterexample, in which a particle makes quantum transitions between the sites of a d-dimensional hypercubic lattice while strongly coupled to a bath of two-level systems that “record” the transitions. The long-time evolution of an initial wave packet is found to be most unusual: the mean square displacement of the particle density matrix shows long-range ballistic behavior, with ⟨n2⟩∼t2, but simultaneously a kind of weakly localized behavior near …
The Origin Of The Phase In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe
The Origin Of The Phase In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe
Physics Department Faculty Publication Series
We consider the interference of two overlapping ideal Bose-Einstein condensates. The usual description of this phenomenon involves the introduction of a condensate wave function with a definite phase. We investigate the origin of this phase and the theoretical basis of treating interference. It is possible to construct a phase state for which the particle number is uncertain, but the phase is known. How such a state would be prepared before an experiment is not obvious. We show that a phase can also arise from experiments using condensates with known particle numbers. The analysis of measurements in such states also gives …