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Sigma Exchange In The Nuclear Force And Effective Field Theory, John Donoghue

John Donoghue

In the phenomenological description of the nuclear interaction a crucial 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 …

Vortex Matter, Effective Magnetic Charges, And Generalizations Of Dipolar Superfluidity Concept In Layered Systems, Egor Babaev

Egor Babaev

In the first part of this letter we discuss electrodynamics of an excitonic condensate in a bilayer. We show that under certain conditions the system has a dominant energy scale and is described by the effective electrodynamics with "planar magnetic charges". In the second part of the paper we point out that a vortex liquid state in bilayer superconductors also possesses dipolar superfluid modes and establish equivalence mapping between this state and a dipolar excitonic condensate. We point out that a vortex liquid state in an N-layer superconductor possesses multiple topologically coupled dipolar superfluid modes and therefore represents a generalization …

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 …

The Nuclear Central Force In The Chiral Limit, John Donoghue

John Donoghue

Chiral perturbation theory supplemented by the Omnes function is employed to study the strength of the isoscalar central nuclear interaction, G_S, in the chiral limit vs the physical case. A very large modification is seen, i.e. eta_s = G_S ~ chiral /G_S ~ 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, d_S, is also calculated and is correspondingly large. I also explain …

Undulated Cylinders Of Charged Diblock Copolymers, Gregory M. Grason, Christian Santangelo

Christian Santangelo

We study the cylinder to sphere morphological transition of diblock copolymers in aqueous solution with a hydrophobic block and a charged block. We find a metastable undulated cylinder configuration for a range of charge and salt concentrations which, nevertheless, occurs above the threshold where spheres are thermodynamically favorable. By modeling the shape of the cylinder ends, we find that the free-energy barrier for the transition from cylinders to spheres is quite large and that this barrier falls significantly in the limit of high polymer charge and low solution salinity. This suggests that observed undulated cylinder phases are kinetically trapped structures.

Quark And Lepton Masses And Mixing In The Landscape, John Donoghue, Koushik Dutta, Andreas Ross

John Donoghue

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, rho(m) ~ 1/m. If we extend this distribution to include all the Yukawa couplings, we show that the resulting CKM 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 …

Smectic Liquid Crystals: Materials With One-Dimensional, Periodic Order, Randall D. Kamien, Christian Santangelo

Christian Santangelo

Smectic liquid crystals are materials formed by stacking deformable, fluid layers. Although smectics prefer to have flat, uniformly-spaced layers, boundary conditions can impose curvature on the layers. Since the layer spacing and curvature are intertwined, the problem of finding minimal configurations for the layers becomes nontrivial. We discuss various topological and geometrical aspects of these materials and present recent progress on finding some exact layer configurations. We also exhibit connections to the study of certain embedded minimal surfaces and briefly summarize some important open problems.

2006 Newsletter, Morton Sternheim

STEM Education Institute Newsletters

Conference on Alternative Certification for Science Teachers

Nanotechnology p. 2

STEM Earth Central p. 3

Science and Engineering Saturday Seminars p. 8

Nutrition and Health in the Science Classroom p. 10

Science Exhibit and Demo p. 11

STEM Adventures p. 5

Noyce Scholars p. 10

PV STEMNET Looks to Future Funding p. 5

Spring Semester Field Trips p. 6

STEM Connections Ends p. 7

STEMTEC Faculty Development Programs p. 9

Farewell to STEMTEC p. 9

Department Of Physics Newsletter: Spring 2006, Bob Krotkov, Ken Langley, Gerry Peterson, Monroe Rabin, Hajime Sakai, Elena Sharnoff

Physics Newsletters

No abstract provided.

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

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

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

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

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

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

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

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.

High Precision Measurement Of The Thermal Exponent For The Three-Dimensional Xy Universality Class, Evgeni Burovski, Jonathan Machta, Nikolay Prokof'ev, Boris Svitunov

Jonathan Machta

Simulation results are reported for the critical point of the two-component ϕ4 field theory. The correlation-length exponent is measured to high precision with the result ν=0.6717(3). This value is in agreement with recent simulation results [Campostrini et al., Phys. Rev. B 63, 214503 (2001)] and marginally agrees with the most recent space-based measurements of the superfluid transition in He4 [Lipa et al., Phys. Rev. B 68, 174518 (2003)].

Elliptic Phases: A Study Of The Nonlinear Elasticity Of Twist-Grain Boundaries, Christian Santangelo, Randall D. Kamien

Christian Santangelo

We develop an explicit and tractable representation of a twist-grain-boundary phase of a smectic-A liquid crystal. This allows us to calculate the interaction energy between grain boundaries and the relative contributions from the bending and compression deformations. We discuss the special stability of the π/2 grain boundaries and discuss the relation of this structure to the Schwarz D surface.

Crossover States Of Vortex Matter In Trapped Bose Condensates, S. Kragset, Egor Babaev, A. Sudbo

Egor Babaev

We perform Monte Carlo studies of vortices in three dimensions in a cylindrical confinement, with uniform and nonuniform density. The former is relevant to rotating 4He, the latter is relevant to a rotating trapped Bose condensate. In the former case we find dominant angular thermal vortex fluctuations close to the cylinder wall. For the latter case, a novel effect is that at low temperatures the vortex solid close to the center of the trap crosses directly over to a tension-less vortex tangle near the edge of the trap. At higher temperatures an intermediate tension-full vortex liquid located between the vortex …

Complexity, Parallel Computation And Statistical Physics, Jonathan Machta

Jonathan Machta

The intuition that a long history is required for the emergence of complexity in natural systems is formalized using the notion of depth. The depth of a system is defined in terms of the number of parallel computational steps needed to simulate it. Depth provides an objective, irreducible measure of history that is applicable to systems of the kind studied in statistical physics. It is argued that physical complexity cannot occur in the absence of substantial depth and that depth is a useful proxy for physical complexity. The ideas are illustrated for a variety of systems in statistical physics

Ergodic Properties Of Markov Processes, L Rey-Bellet

Luc Rey-Bellet

In these notes we discuss Markov processes, in particular stochastic differential equations (SDE) and develop some tools to analyze their long-time behavior. There are several ways to analyze such properties, and our point of view will be to use systematically Liapunov functions which allow a nice characterization of the ergodic properties. In this we follow, at least in spirit, the excellent book of Meyn and Tweedie [7]. In general a Liapunov function W is a positive function which grows at infinity and satisfies an inequality involving the generator of the Markov process L: roughly speaking we have the implications (α …

Parity-Violating Electron Scattering From ^4 He And The Strange Electric Form Factor Of The The Nucleon, K. A. Aniol, D. S. Armstrong, T. Averett, H. Benaoum, P. Y. Bertin, E. Burtin, J. Cahoon, G. D. Cates, C. C. Chang, Y. C. Chao, J. P. Chen, Seonho Choi, E. Chudakov, B. Craver, F. Cusanno, P. Decowsky, D. Deepa, C. Ferdi, R. J. Feuerbach, M. J. Finn, S. Frullani, K. Fuoti, F. Garibaldi, R. Gilman, A. Glamazdin, V. Gorbenko, J. M. Grames, J. Hansknecht, D. W. Higinbotham, R. Holmes, T. Holmstrom, T. B. Humensky, H. Ibrahim, C. W. De Jager, X. Jiang, L. J. Kaufman, A. Kelleher, A. Kolarkar, S. Kowalski, Krishna Kumar, D. Lambert, P. Laviolette, J. Lerose, D. Lhuillier, N. Liyanage, D. J. Margaziotis, M. Mazouz, K. Mccormick, D. G. Meekins, Z. E. Meziani, R. Michaels, B. Moffit, P. Monaghan, C. Munoz-Camacho, S. Nanda, V. Nelyubin, D. Neyret, K. D. Paschke, M. Poelker, R. Pomatsalyuk, Y. Qiang, B. Reitz, J. Roche, A. Saha, J. Singh, R. Snyder, P. A. Souder, R. Subedi, R. Suleiman, V. Sulkosky, W. A. Tobias, G. M. Urciuoli, A. Vacheret, E. Voutier, K. Wang, R. Wilson, B. Wojtsekhowski, X. Zheng

Krishna Kumar

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 4He at an average scattering angle = 5.7 degrees and a four-momentum transfer Q2 = 0.091 GeV2 . From these data, for the first time, the strange electric form factor of the nucleon G(E)s can be isolated. The measured asymmetry of A(PV) = (6.72 +/- 0.84(stat) +/- 0.21(syst) x 10(-6) yields a value of G(E)s = -0.038 +/- 0.042(stat) +/- 0.010(syst), consistent with zero.

Numerical Study Of The Random Field Ising Model At Zero And Positive Temperature, Yong Wu, Jonathan Machta

Jonathan Machta

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 …

Computing Counterion Densities At Intermediate Coupling, Christian Santangelo

Christian Santangelo

By decomposing the Coulomb interaction into a long-distance component appropriate for mean-field theory, and a non-mean-field short distance component, we compute the counterion density near a charged surface for all values of the counterion coupling parameter. A modified strong-coupling expansion that is manifestly finite at all coupling strengths is used to treat the short-distance component. We find a nonperturbative correction related to the lateral counterion correlations that modifies the density at intermediate coupling.

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

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

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

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

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 …