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2010

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Articles 31 - 58 of 58

Full-Text Articles in Physical Sciences and Mathematics

Realization Of Center Symmetry In Two Adjoint Flavor Large-N Yang-Mills, Simon Catterall, Richard Galvez, Mithat Unsal Jun 2010

Realization Of Center Symmetry In Two Adjoint Flavor Large-N Yang-Mills, Simon Catterall, Richard Galvez, Mithat Unsal

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We report on the results of numerical simulations of SU(N) lattice Yang Mills with two flavors of (light) Wilson fermion in the adjoint representation. We analytically and numerically address the question of center symmetry realization on lattices with \Gamma sites in each direction in the large-N limit. We show, by a weak coupling calculation that, for massless fermions, center symmetry realization is independent of \Gamma, and is unbroken. Then, we extend our result by conducting simulations at non zero mass and finite gauge coupling. Our results indicate that center symmetry is intact for a range of fermion mass in the …

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Supersymmetric Lattices, Simon Catterall Jun 2010

Supersymmetric Lattices, Simon Catterall

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Discretization of supersymmetric theories is an old problem in lattice field theory. It has resisted solution until quite recently when new ideas drawn from orbifold constructions and topological field theory have been brought to bear on the question. The result has been the creation of a new class of lattice gauge theory in which the lattice action is invariant under one or more supersymmetries. The resultant theories are local and free of doublers and in the case of Yang-Mills theories also possess exact gauge invariance. In principle they form the basis for a truly non-perturbative definition of the continuum supersymmetric …

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Branching Fractions For Chi_Cj -> P P-Bar Pi^0, P P-Bar Eta, And P P-Bar Omega, Raymond Mountain, Marina Artuso, S. Blusk, R. Mountain May 2010

Branching Fractions For Chi_Cj -> P P-Bar Pi^0, P P-Bar Eta, And P P-Bar Omega, Raymond Mountain, Marina Artuso, S. Blusk, R. Mountain

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Using a sample of 25.9 million psi(2S) decays acquired with the CLEO-c detector at the CESR e^+e^- collider, we report branching fractions for the decays chi_cJ -> p p-bar pi^0, p p-bar eta, and p p-bar omega, with J=0,1,2. Our results for B(chi_cJ-> p p-bar pi^0) and B(chi_cJ-> p p-bar eta) are consistent with, but more precise than, previous measurements. Furthermore, we include the first measurement of B(chi_cJ-> p p-bar omega).

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Branching Fractions For Χcj → Ppπ0, Ppη, And Ppω, Raymond Mountain, Marina Artuso, S. Blusk, T. Skwarnicki May 2010

Branching Fractions For Χcj → Ppπ0, Ppη, And Ppω, Raymond Mountain, Marina Artuso, S. Blusk, T. Skwarnicki

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Using a sample of 25.9 million psi(2S) decays acquired with the CLEO-c detector at the CESR e^+e^- collider, we report branching fractions for the decays chi_cJ -> p p-bar pi^0, p p-bar eta, and p p-bar omega, with J=0,1,2. Our results for B(chi_cJ-> p p-bar pi^0) and B(chi_cJ-> p p-bar eta) are consistent with, but more precise than, previous measurements. Furthermore, we include the first measurement of B(chi_cJ-> p p-bar omega).

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Light Scalar Puzzle In Qcd, Joseph Schechter, Amir H. Fariborz, Renata Jora May 2010

Light Scalar Puzzle In Qcd, Joseph Schechter, Amir H. Fariborz, Renata Jora

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An approach to understanding the light scalar meson phenomenology is briefly reviewed.

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Vortex Dynamics In Superconducting Channels With Periodic Constrictions, Britton Plourde, Kang Yu, M.B.S. Hesselberth, P. H. Kes May 2010

Vortex Dynamics In Superconducting Channels With Periodic Constrictions, Britton Plourde, Kang Yu, M.B.S. Hesselberth, P. H. Kes

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Vortices confined to superconducting easy flow channels with periodic constrictions exhibit reversible oscillations in the critical current at which vortices begin moving as the external magnetic field is varied. This commensurability scales with the channel shape and arrangement, although screening effects play an important role. For large magnetic fields, some of the vortices become pinned outside of the channels, leading to magnetic hysteresis in the critical current. Some channel configurations also exhibit a dynamical hysteresis in the flux-flow regime near the matching fields.

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Effective Theory Approach To The Spontaneous Breakdown Of Lorentz Invariance, Christian Armendariz-Picon, Alberto Diez-Tejedor, Riccardo Penco Apr 2010

Effective Theory Approach To The Spontaneous Breakdown Of Lorentz Invariance, Christian Armendariz-Picon, Alberto Diez-Tejedor, Riccardo Penco

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We generalize the coset construction of Callan, Coleman, Wess and Zumino to theories in which the Lorentz group is spontaneously broken down to one of its subgroups. This allows us to write down the most general low-energy effective Lagrangian in which Lorentz invariance is non-linearly realized, and to explore the consequences of broken Lorentz symmetry without having to make any assumptions about the mechanism that triggers the breaking. We carry out the construction both in flat space, in which the Lorentz group is a global spacetime symmetry, and in a generally covariant theory, in which the Lorentz group can be …

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Analysis Of D+ → K-Π+ E+ Νe And D+ → K- Π+ Μ+ Νμ Semileptonic Decays, Raymond Mountain, Marina Artuso, S. Blusk, Sadia Khalil Apr 2010

Analysis Of D+ → K-Π+ E+ Νe And D+ → K- Π+ Μ+ Νμ Semileptonic Decays, Raymond Mountain, Marina Artuso, S. Blusk, Sadia Khalil

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Using a large sample (~11800 events) of D^+ into K^- pi^+ e^+ nu_e and D^+ into K^- pi^+ mu^+ nu_mu decays collected by the CLEO-c detector running at the psi(3770), we measure the helicity basis form factors free from the assumptions of spectroscopic pole dominance and provide new, accurate measurements of the absolute branching fractions for D^+ into K^- pi^+ e^+ nu_e and D^+ into K^- pi^+ mu^+ nu_mu decays. We find branching fractions which are consistent with previous world averages. Our measured helicity basis form factors are consistent with the spectroscopic pole dominance predictions for the three main helicity …

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Analysis Of D+ To K- Pi+ E+ Nu_E And D+ To K- Pi+ Mu+ Nu_Mu Semileptonic Decays, Raymond Mountain, Marina Artuso, S. Blusk, Sadia Khalil Apr 2010

Analysis Of D+ To K- Pi+ E+ Nu_E And D+ To K- Pi+ Mu+ Nu_Mu Semileptonic Decays, Raymond Mountain, Marina Artuso, S. Blusk, Sadia Khalil

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Using a large sample (~11800 events) of D^+ into K^- pi^+ e^+ nu_e and D^+ into K^- pi^+ mu^+ nu_mu decays collected by the CLEO-c detector running at the psi(3770), we measure the helicity basis form factors free from the assumptions of spectroscopic pole dominance and provide new, accurate measurements of the absolute branching fractions for D^+ into K^- pi^+ e^+ nu_e and D^+ into K^- pi^+ mu^+ nu_mu decays. We find branching fractions which are consistent with previous world averages. Our measured helicity basis form factors are consistent with the spectroscopic pole dominance predictions for the three main helicity …

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Fluctuations And Pattern Formation In Self-Propelled Particles, Shradha Mishra, Aparna Baskaran, M. Cristina Marchetti Apr 2010

Fluctuations And Pattern Formation In Self-Propelled Particles, Shradha Mishra, Aparna Baskaran, M. Cristina Marchetti

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We consider a coarse-grained description of a system of self-propelled particles given by hydrodynamic equations for the density and polarization fields. We find that the ordered moving or flocking state of the system is unstable to spatial fluctuations beyond a threshold set by the self-propulsion velocity of the individual units. In this region, the system organizes itself into an inhomogeneous state of well-defined propagating stripes of flocking particles interspersed with low density disordered regions. Further, we find that even in the regime where the homogeneous flocking state is stable, the system exhibits large fluctuations in both density and orientational order. …

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Methods For Reducing False Alarms In Searches For Compact Binary Coalescences In Ligo Data, Duncan Brown, J. Slutsky Apr 2010

Methods For Reducing False Alarms In Searches For Compact Binary Coalescences In Ligo Data, Duncan Brown, J. Slutsky

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The LIGO detectors are sensitive to a variety of noise transients of non-astrophysical origin. Instrumental glitches and environmental disturbances increase the false alarm rate in the searches for gravitational waves. Using times already identified when the interferometers produced data of questionable quality, or when the channels that monitor the interferometer indicated non-stationarity, we have developed techniques to safely and effectively veto false triggers from the compact binary coalescences (CBCs) search pipeline.

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Paraboloidal Crystals, Mark Bowick, Luca Giomi Apr 2010

Paraboloidal Crystals, Mark Bowick, Luca Giomi

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The interplay between order and geometry in soft condensed matter systems is an active field with many striking results and even more open problems. Ordered structures on curved surfaces appear in multi-electron helium bubbles, viral and bacteriophage protein capsids, colloidal self-assembly at interfaces and in physical membranes. Spatial curvature can lead to novel ground state configurations featuring arrays of topological defects that would be excited states in planar systems. We illustrate this with a sequence of images showing the Voronoi lattice (in gold) and the corresponding Delaunay triangulations (in green) for ten low energy configurations of a system of classical …

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Kaluza-Klein Theory With Torsion Confined To The Extra-Dimension, Karthik H. Shankar, Kameshwar C. Wali Apr 2010

Kaluza-Klein Theory With Torsion Confined To The Extra-Dimension, Karthik H. Shankar, Kameshwar C. Wali

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Here we consider a variant of the 5 dimensional Kaluza-Klein theory within the framework of Einstein-Cartan formalism that includes torsion. By imposing a set of constraints on torsion and Ricci rotation coefficients, we show that the torsion components are completely expressed in terms of the metric. Moreover, the Ricci tensor in 5D corresponds exactly to what one would obtain from torsion-free general relativity on a 4D hypersurface. The contributions of the scalar and vector elds of the standard K-K theory to the Ricci tensor and the affine connections are completely nulli ed by the contributions from torsion. As a consequence, …

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Topological Gravity On The Lattice, Simon Catterall Mar 2010

Topological Gravity On The Lattice, Simon Catterall

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In this paper we show that a particular twist of \cN=4 super Yang-Mills in three dimensions with gauge group SU(2) possesses a set of classical vacua corresponding to the space of flat connections of the {\it complexified} gauge group SL(2,C). The theory also contains a set of topological observables corresponding to Wilson loops wrapping non-trivial cycles of the base manifold. This moduli space and set of topological observables is shared with the Chern Simons formulation of three dimensional gravity and we hence conjecture that the Yang-Mills theory gives an equivalent description of the gravitational theory. Unlike the Chern Simons formulation …

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A Unified Approach To Cosmic Acceleration, Scott Watson, Minjoon Park, Kathryn M. Zurek Mar 2010

A Unified Approach To Cosmic Acceleration, Scott Watson, Minjoon Park, Kathryn M. Zurek

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We present a unified framework for the study of late time cosmic acceleration. Using methods of effective field theory, we show that existing proposals for late time acceleration can be subsumed in a single framework, rather than many compartmentalized theories. We construct the most general action consistent with symmetry principles, derive the background and perturbation evolution equations, and demonstrate that for special choices of our parameters we can reproduce results already existing in the literature. Lastly, we lay the foundation for future work placing phenomenological constraints on the parameters of the effective theory. Although in this paper we focus on …

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Primordial Perturbations In Einstein-Aether And Bpsh Theories, Christian Armendariz-Picon, Noela Farina Sierra, Jaume Garriga Mar 2010

Primordial Perturbations In Einstein-Aether And Bpsh Theories, Christian Armendariz-Picon, Noela Farina Sierra, Jaume Garriga

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We study the primordial perturbations generated during a stage of single-field inflation in Einstein-aether theories. Quantum fluctuations of the inflaton and aether fields seed long wavelength adiabatic and isocurvature scalar perturbations, as well as transverse vector perturbations. Geometrically, the isocurvature mode is the potential for the velocity field of the aether with respect to matter. For a certain range of parameters, this mode may lead to a sizable random velocity of the aether within the observable universe. The adiabatic mode corresponds to curvature perturbations of co-moving slices (where matter is at rest). In contrast with the standard case, it has …

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Nonequilibrium Statistical Mechanics Of Self-Propelled Hard Rods, Aparna Baskaran, M. Cristina Marchetti Feb 2010

Nonequilibrium Statistical Mechanics Of Self-Propelled Hard Rods, Aparna Baskaran, M. Cristina Marchetti

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Using tools of nonequilibirum mechanics, we study a model of self-propelled hard rods on a substrate in two dimensions to quantify the interplay of self-propulsion and excluded-volume effects. We derive of a Smoluchowski equation for the configurational probability density of self-propelled rods that contains several modifications as compared to the familiar Smoluchowski equation for thermal rods. As a side-product of out work, we also present a purely dynamical derivation of the Onsager form of the mean field excluded volume interaction among thermal hard rods.

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Sheared Active Fluids: Thickening, Thinning And Vanishing Viscosity, Luca Giomi, Tanniemola B. Liverpool, M. Cristina Marchetti Feb 2010

Sheared Active Fluids: Thickening, Thinning And Vanishing Viscosity, Luca Giomi, Tanniemola B. Liverpool, M. Cristina Marchetti

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We analyze the behavior of a suspension of active polar particles under shear. In the absence of external forces, orientationally ordered active particles are known to exhibit a transition to a state of non-uniform polarization and spontaneous flow. Such a transition results from the interplay between elastic stresses, due to the liquid crystallinity of the suspension, and internal active stresses. In the presence of an external shear we find an extremely rich variety of phenomena, including an effective reduction (increase) in the apparent viscosity depending on the nature of the active stresses and the flow-alignment property of the particles, as …

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Logic Is To The Quantum As Geometry Is To Gravity, Rafael D. Sorkin Jan 2010

Logic Is To The Quantum As Geometry Is To Gravity, Rafael D. Sorkin

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will propose that the reality to which the quantum formalism implicitly refers is a kind of generalized history, the word history having here the same meaning as in the phrase sum-over-histories. This proposal confers a certain independence on the concept of event, and it modifies the rules of inference concerning events in order to resolve a contradiction between the idea of reality as a single history and the principle that events of zero measure cannot happen (the Kochen-Specker paradox being a classic expression of this contradiction). The so-called measurement problem is then solved if macroscopic events satisfy classical rules of …

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Covariant Quantum Fields On Noncommutative Spacetimes, A. P. Balachandran, A. Ibort, G. Marmo, M. Martone Jan 2010

Covariant Quantum Fields On Noncommutative Spacetimes, A. P. Balachandran, A. Ibort, G. Marmo, M. Martone

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A spinless covariant field $\phi$ on Minkowski spacetime $\M^{d+1}$ obeys the relation $U(a,\Lambda)\phi(x)U(a,\Lambda)^{-1}=\phi(\Lambda x+a)$ where $(a,\Lambda)$ is an element of the Poincar\'e group $\Pg$ and $U:(a,\Lambda)\to U(a,\Lambda)$ is its unitary representation on quantum vector states. It expresses the fact that Poincar\'e transformations are being unitary implemented. It has a classical analogy where field covariance shows that Poincar\'e transformations are canonically implemented. Covariance is self-reproducing: products of covariant fields are covariant. We recall these properties and use them to formulate the notion of covariant quantum fields on noncommutative spacetimes. In this way all our earlier results on dressing, statistics, etc. for …

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Discreteness And The Transmission Of Light From Distant Sources, Fay Dowker, Joe Henson, Rafael Sorkin Jan 2010

Discreteness And The Transmission Of Light From Distant Sources, Fay Dowker, Joe Henson, Rafael Sorkin

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We model the classical transmission of a massless scalar field from a source to a detector on a background causal set. The predictions do not differ significantly from those of the continuum. Thus, introducing an intrinsic inexactitude to lengths and durations - or more specifically, replacing the Lorentzian manifold with an underlying discrete structure - need not disrupt the usual dynamics of propagation.

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Quantum Geons And Noncommutative Spacetimes, A. P. Balachandran, A. Ibort, G. Marmo, M. Martone Jan 2010

Quantum Geons And Noncommutative Spacetimes, A. P. Balachandran, A. Ibort, G. Marmo, M. Martone

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Physical considerations strongly indicate that spacetime at Planck scales is noncommutative. A popular model for such a spacetime is the Moyal plane. The Poincare group algebra acts on it with a Drinfel'd-twisted coproduct. But the latter is not appropriate for more complicated spacetimes such as those containing the Friedman-Sorkin (topological) geons. They have rich diffeomorphism groups and in particular mapping class groups, so that the statistics groups for N identical geons is strikingly different from the permutation group SN. We generalise the Drinfel'd twist to (essentially) generic groups including to finite and discrete ones and use it to modify the …

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S-Waves And The Extraction Of Beta_S, Sheldon Stone Jan 2010

S-Waves And The Extraction Of Beta_S, Sheldon Stone

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The CP Violating asymmetry in Bs mixing (beta_s) is one of the most promising measurements where physics beyond the Standard Model could be revealed. As such, analyses need to be subjected to great scrutiny. The mode Bs -> J/psi\phi has been used, and the mode Bs -> \phi \phi proposed for future measurements. These modes both have two vector particles in the final state and thus angular analyses must be used to disentangle the contributions from CP+ and CP- configurations. The angular distributions, however, could be distorted by the presence of S-waves masquerading as low mass K+K- pairs, that could …

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Vortex Dynamics In Superconducting Channels With Periodic Constrictions, Kang Yu, M.B.S. Hesselberth, P. H. Kes, B.L.T. Plourde Jan 2010

Vortex Dynamics In Superconducting Channels With Periodic Constrictions, Kang Yu, M.B.S. Hesselberth, P. H. Kes, B.L.T. Plourde

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Vortices confined to superconducting easy flow channels with periodic constrictions exhibit reversible oscillations in the critical current at which vortices begin moving as the external magnetic field is varied. This commensurability scales with the channel shape and arrangement, although screening effects play an important role. For large magnetic fields, some of the vortices become pinned outside of the channels, leading to magnetic hysteresis in the critical current. Some channel configurations also exhibit a dynamical hysteresis in the flux-flow regime near the matching fields.

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Nonperturbative Results For Yang-Mills Theories, Francesco Sannino, Joseph Schechter Jan 2010

Nonperturbative Results For Yang-Mills Theories, Francesco Sannino, Joseph Schechter

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Some non perturbative aspects of the pure SU(3) Yang-Mills theory are investigated assuming a specific form of the beta function, based on a recent modification by Ryttov and Sannino of the known one for supersymmetric gauge theories. The characteristic feature is a pole at a particular value of the coupling constant, g. First it is noted, using dimensional analysis, that physical quantities behave smoothly as one travels from one side of the pole to the other. Then it is argued that the form of the integrated beta function g(m), where m is the mass scale, determines the mass gap of …

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Light Scalar Puzzle In Qcd, Amir H. Fariborz, Renata Jora, Joseph Schechter Jan 2010

Light Scalar Puzzle In Qcd, Amir H. Fariborz, Renata Jora, Joseph Schechter

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An approach to understanding the light scalar meson spectroscopy is briefly reviewed

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To What Type Of Logic Does The "Tetralemma" Belong?, Rafael D. Sorkin Jan 2010

To What Type Of Logic Does The "Tetralemma" Belong?, Rafael D. Sorkin

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Although the so called "tetralemma" might seem to be incompatible with any recognized scheme of logical inference, its four alternatives arise naturally within the "anhomomorphic" logics proposed recently in order to accommodate certain features of microscopic (i.e. quantum) physics. This suggests that non-classical logics of a similar type might have been known in ancient India.

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Plasmonic Light-Trapping And Quantum Efficiency Measurements On Nanocrystalline Silicon Solar Cells And Silicon-On-Insulator Devices, Eric A. Schiff, Hui Zhao, Birol Ozturk, Baojie Yan, Jeff Yang Jan 2010

Plasmonic Light-Trapping And Quantum Efficiency Measurements On Nanocrystalline Silicon Solar Cells And Silicon-On-Insulator Devices, Eric A. Schiff, Hui Zhao, Birol Ozturk, Baojie Yan, Jeff Yang

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Quantum efficiency measurements in nanocrystalline silicon (nc-Si:H)solar cells deposited onto textured substrates indicate that these cells are close to the "stochastic lighttrapping limit" proposed by Yablonovitch in the 1980s. An interesting alternative to texturing is "plasmonic" light-trapping based on non-textured cells and using an overlayer of metallic nanoparticles to produce light-trapping. While this type of light-trapping has not yet been demonstrated for nc-Si:H solar cells, significant photocurrent enhancements have been reported on silicon-on-insulator devices with similar optical properties to nc-Si:H. Here we report our measurements of quantum efficiencies in nc-Si:H solar cells and normalized photoconductance spectra in SOI photodetectors with …

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