Physical Sciences and Mathematics Commons^™

Holographic Representation Of Bulk Fields With Spin In Ads/Cft, Daniel N. Kabat, Gilad Lifschytz, Shubho Roy, Debajyoti Sarkar

Publications and Research

We develop the representation of bulk fields with spin one and spin two in anti-de Sitter space, as non-local observables in the dual CFT. Working in holographic gauge in the bulk, at leading order in 1/N bulk gauge fields are obtained by smearing boundary currents over a sphere on the complexified boundary, while linearized metric fluctuations are obtained by smearing the boundary stress tensor over a ball. This representation respects AdS covariance up to a compensating gauge transformation. We also consider massive vector fields, where the bulk field is obtained by smearing a non-conserved current. We compute bulk two-point functions …

Quantum Deflagration And Supersonic Fronts Of Tunneling In Molecular Magnets, Dmitry A. Garanin, Saaber Shoyed

Publications and Research

Theory of magnetic deflagration taking into account dipolar-controlled spin tunneling has been applied to the realistic model of molecular magnet Mn_12 Ac. At small transverse field, the front speed v has tunneling maxima on the bias field B_z reflecting those of the molecular spin's relaxation rate calculated from the density-matrix equation. At high transverse field, spin tunneling directly out of the metastable ground state leads to front speeds that can exceed the speed of sound. Both for the weak and strong transverse field, the spatial profile of the deflagration front near tunneling resonances shows a front of tunneling that triggers …

Optomechanics Of Cavity Driven Nanoparticles, Joel T. Rubin

Dissertations, Theses, and Capstone Projects

The subject of this thesis is the opto-mechanical interaction of a spherical high-Q microresonator and a subwavelength particle, which, at optical wavelengths, corresponds to a size on the order of nanometers. After a review of the basic theory of spherical resonators and multi-sphere scattering, the full self-consistent electromagnetic field of the coupled resonator-particle system is derived. The particle-induced frequency shift and broadening is calculated by examining the poles of the scattering coefficients of the resonator. The force exerted on the particle by the field is determined via the Maxwell stress tensor, and is found to be in general non-conservative. From …

Aperture Array Photonic Metamaterials: Theoretical Approaches, Numerical Techniques And A Novel Application, Eli Lansey

Dissertations, Theses, and Capstone Projects

Optical or photonic metamaterials that operate in the infrared and visible frequency regimes show tremendous promise for solving problems in renewable energy, infrared imaging, and telecommunications. However, many of the theoretical and simulation techniques used at lower frequencies are not applicable to this higher-frequency regime. Furthermore, technological and financial limitations of photonic metamaterial fabrication increases the importance of reliable theoretical models and computational techniques for predicting the optical response of photonic metamaterials.

This thesis focuses on aperture array metamaterials. That is, a rectangular, circular, or other shaped cavity or hole embedded in, or penetrating through a metal film. The research …

Wave-Function Functionals For The Density, Marlina Slamet, Xiao-Yin Pan, Viraht Sahni

Publications and Research

We extend the idea of the constrained-search variational method for the construction of wave-function functionals psi[chi] of functions chi. The search is constrained to those functions chi such that psi[chi] reproduces the density rho(r) while simultaneously leading to an upper bound to the energy. The functionals are thereby normalized and automatically satisfy the electron-nucleus coalescence condition. The functionals psi[chi] are also constructed to satisfy the electron-electron coalescence condition. The method is applied to the ground state of the helium atom to construct functionals psi[chi] that reproduce the density as given by the Kinoshita correlated wave function. The expectation of single-particle …

Graded Index And Randomly Oriented Core-Shell Silicon Nanowires With Broadband And Wide Angle Antireflection, P. Pignalosa, H. Lee, L. Qiao, M. Tseng, Y. Yi

Publications and Research

Antireflection with broadband and wide angle properties is important for a wide range of applications on photovoltaic cells and display. The SiOx shell layer provides a natural antireflection from air to the Si core absorption layer. In this work, we have demonstrated the random core-shell silicon nanowires with both broadband (from 400nm to 900nm) and wide angle (from normal incidence to 60o) antireflection characteristics within AM1.5 solar spectrum. The graded index structure from the randomly oriented core-shell (Air/SiOx/Si) nanowires may provide a potential avenue to realize a broadband and wide angle antireflection layer

Two-Loop Leading Color Corrections To Heavy-Quark Pair Production In The Gluon Fusion Channel, R. Bonciani, Andrea Ferroglia, T. Gehrmann, A. Von Manteuffel, C. Studerus

Publications and Research

We evaluate the two-loop QCD diagrams contributing to the leading color coefficient of the heavy-quark pair production cross section in the gluon fusion channel. We obtain an analytic expression, which is valid for any value of the Mandelstam invariants s and t and of the heavy-quark mass m. Our findings agree with previous analytic results in the small-mass limit and with recent results for the coefficients of the IR poles.

Climate Change: The Fork At The End Of Now, Micha Tomkiewicz

Publications and Research

There are many books on global warming written entirely from a layman's perspective, and there is a great deal of scientific literature on this subject. But few if any books attempt to bridge the science to those who lack a rigorous background in mathematics, physics and chemistry-but who may be working on careers in environmental science and policy. The new text is designed to introduce the field of global climate change from a scientific perspective-but written in a way that is accessible to students with some or little science background. It reviews the basic principles of climatic thermodynamics and atmospheric …

Differential Microlensing Measurements Of Quasar Broad-Line Kinematics In Q2237+0305, Matthew J. O'Dowd, N F. Bate, R L. Webster, R Wayth

Publications and Research

The detailed workings of the central engines of powerful quasars remain a mystery. This is primarily due to the fact that, at their cosmological distances, the inner regions of these quasars are spatially unresolvable. Reverberation mapping is now beginning to unlock the physics of the Broad Emission Line Region (BELR) in nearby, low-luminosity quasars, however it is still unknown whether this gas is dominated by virial motion, by outflows, or infall. The challenge is greater for more distant, powerful sources due to the very long response time of the BELR to changes in the continuum. We present a new technique …

Physics Professor Leads Research Into Laser Uses, Aldemaro Romero Jr.

Publications and Research

No abstract provided.

A Bulk Inflaton From Large-Volume Extra Dimensions, Brian Greene, Daniel N. Kabat, Janna Levin, Dylan Thurston

Publications and Research

The universe may have extra spatial dimensions with large volume that we cannot perceive because the energy required to excite modes in the extra directions is too high. Many examples are known of such manifolds with a large volume and a large mass gap. These compactifications can help explain the weakness of four-dimensional gravity and, as we show here, they also have the capacity to produce reasonable potentials for an inflaton field. Modeling the inflaton as a bulk scalar field, it becomes very weakly coupled in four dimensions, and this enables us to build phenomenologically acceptable inflationary models with tunings …

Dissipative Macroscopic Quantum Tunneling In Type-I Superconductors, Ricardo Zarzuela, Eugene M. Chudnovsky, Javier Tejada

Publications and Research

We study macroscopic quantum tunneling of interfaces separating normal and superconducting regions in type-I superconductors. Mathematical model is developed, that describes dissipative quantum escape of a two-dimensional manifold from a planar potential well. It corresponds to, e.g., a current-driven quantum depinning of the interface from a grain boundary or from artificially manufactured pinning layer. Effective action is derived and instantons of the equations of motion are investigated. Crossover between thermal activation and quantum tunneling is studied and the crossover temperature is computed. Our results, together with recent observation of non-thermal low-temperature magnetic relaxation in lead, suggest possibility of a controlled …

Renormalization Of The Tunnel Splitting In A Rotating Nanomagnet, Michael F. O'Keeffe, Eugene M. Chudnovsky

Publications and Research

We study spin tunneling in a magnetic nanoparticle with biaxial anisotropy that is free to rotate about its anisotropy axis. Exact instanton of the coupled equations of motion is found that connects degenerate classical energy minima. We show that mechanical freedom of the particle renormalizes magnetic anisotropy and increases the tunnel splitting.

Constructing Local Bulk Observables In Interacting Ads/Cft, Daniel N. Kabat, Gilad Lifschytz, David A. Lowe

Publications and Research

Local operators in the bulk of AdS can be represented as smeared operators in the dual CFT. We show how to construct these bulk observables by requiring that the bulk operators commute at spacelike separation. This extends our previous work by taking interactions into account. Large-N factorization plays a key role in the construction. We show diagrammatically how this procedure is related to bulk Feynman diagrams.

Quantum Entanglement Of A Tunneling Spin With Mechanical Modes Of A Torsional Resonator, Dmitry A. Garanin, Eugene M. Chudnovsky

Publications and Research

We solve Schr\"odinger equation describing a tunneling macrospin coupled to a torsional oscillator. Energy spectrum is studied for various quantum regimes. Magnetic susceptibility and noise spectrum are computed. We show that entanglement of the spin with mechanical modes of a subnanometer oscillator results in the decoherence of spin tunneling. For larger oscillators the presence of a tunneling spin can be detected through splitting of the mechanical mode at the resonance. Our results apply to experiments with magnetic molecules coupled to nanoresonators.

Quantum Tunneling Of The Interfaces Between Normal-Metal And Superconducting Regions Of A Type-I Pb Superconductor, Eugene M. Chudnovsky, S Velez, A Garcia-Santiago, J A. Hernandez

Publications and Research

Evidence of a non-thermal magnetic relaxation in the intermediate state of a type-I superconducor is presented. It is attributed to quantum tunneling of interfaces separating normal and superconducting regions. Tunneling barriers are estimated and temperature of the crossover from thermal to quantum regime is obtained from Caldeira-Leggett theory. Comparison between theory and experiment points to tunneling of interface segments of size comparable to the coherence length, by steps of order one nanometer.

Thermal Diffractive Corrections To Casimir Energies, Daniel N. Kabat, Dimitra Karabali

Publications and Research

We study the interplay of thermal and diffractive effects in Casimir energies. We consider plates with edges, oriented either parallel or perpendicular to each other, as well as a single plate with a slit. We compute the Casimir energy at finite temperature using a formalism in which the diffractive effects are encoded in a lower dimensional non-local field theory that lives in the gap between the plates. The formalism allows for a clean separation between direct or geometric effects and diffractive effects, and makes an analytic derivation of the temperature dependence of the free energy possible. At low temperatures, with …

Ssgss: The Spitzer-Sdss-Galex Spectroscopic Survey, Matthew J. O'Dowd, David Schiminovich, Benjamin D. Johnson, Marie A. Treyer

Publications and Research

The Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) provides a new sample of 101 star-forming galaxies at z < 0.2 with unprecedented multi-wavelength coverage. New mid- to far-infrared spectroscopy from the Spitzer Space Telescope is added to a rich suite of previous imaging and spectroscopy, including ROSAT, Galaxy Evolution Explorer, Sloan Digital Sky Survey, Two Micron All Sky Survey, and Spitzer/SWIRE. Sample selection ensures an even coverage of the full range of normal galaxy properties, spanning two orders of magnitude in stellar mass, color, and dust attenuation. In this paper we present the SSGSS data set, describe the science drivers, and detail the sample selection, observations, data reduction, and quality assessment. Also in this paper, we compare the shape of the thermal continuum and the degree of silicate absorption of these typical, star-forming galaxies to those of starburst galaxies. We investigate the link between star formation rate, infrared luminosity, and total polycyclic aromatic hydrocarbon luminosity, with a view to calibrating the latter for spectral energy distribution models in photometric samples and at high redshift. Last, we take advantage of the 5-40 micron spectroscopic and far-infrared photometric coverage of this sample to perform detailed fitting of the Draine et al. dust models, and investigate the link between dust mass and star formation history and active galactic nucleus properties.

Hořava Gravity: Symmetries And Generalized Particle Dynamics, Dario Capasso

Dissertations, Theses, and Capstone Projects

In the search for a theory of Quantum Gravity a new proposal was recently made by P. Hořava. The main feature of this new proposed theory is that it is power-counting renormalizable by construction, and could prove to be truly renormalizable, although more work is needed in this direction.

The renormalizability of the theory is a central issue. Indeed, General Relativity does not have this property, implying that to construct its quantum version we need to “complete” the theory in the UV. Hořava suggested a possible way to provide a UV completion of GR by giving up full spacetime reparametrization …

Tensorial Reconstruction At The Integrand Level, G. Heinrich, Giovanni Ossola, T. Reiter, F. Tramontano

Publications and Research

We present a new approach to the reduction of one-loop amplitudes obtained by reconstructing the tensorial expression of the scattering amplitudes. The reconstruction is performed at the integrand level by means of a sampling in the integration momentum. There are several interesting applications of this novel method within existing techniques for the reduction of one-loop multi-leg amplitudes: to deal with numerically unstable points, such as in the vicinity of a vanishing Gram determinant; to allow for a sampling of the numerator function based on real values of the integration momentum; to optimize the numerical reduction in the case of long …

Scattering Amplitudes From Unitarity-Based Reduction Algorithm At The Integrand-Level, P. Mastrolia, Giovanni Ossola, T. Reiter, F. Tramontano

Publications and Research

Samurai is a tool for the automated numerical evaluation of one-loop corrections to any scattering amplitudes within the dimensional-regularization scheme. It is based on the decomposition of the integrand according to the OPP-approach, extended to accommodate an implementation of the generalized d-dimensional unitarity-cuts technique, and uses a polynomial interpolation exploiting the Discrete Fourier Transform. samurai can process integrands written either as numerator of Feynman diagrams or as product of tree-level amplitudes. We discuss some applications, among which the 6- and 8-photon scattering in QED, and the 6-quark scattering in QCD. samurai has been implemented as a Fortran90 library, publicly available, …

On The Feasibility Of A Timely Transition To A More Sustainable Energy Future, Micha Tomkiewicz

Publications and Research

The paper uses the framework of the IPAT equation, as applied to CO2 emission, to decompose the various driving forces in the global energy use. Data from recent history are superimposed on projections of SRES IPCC scenarios to determine if enough sustainable capacity can be built to prevent irreversible ecological deterioration. The conclusion from the analysis is that, in agreement with the IPCC 4th report, until about 2030 there are no large differences between a sustainable scenario and the one that resembles “business as usual”. The sharp divergence that follows stems from different estimates in population growth and in the …

Deflagration With Quantum And Dipolar Effects In A Model Of A Molecular Magnet, Dmitry A. Garanin

Publications and Research

Combination of the thermal effet in magnetic deflagration with resonance spin tunneling controlled by the dipole-dipole interaction in molecular magnets leads to the increase of the deflagration speed in the dipolar window near tunneling resonances.

Rotational Doppler Effect In Magnetic Resonance, S Ledinez, Eugene M. Chudnovsky, Javier Tejada

Publications and Research

We compute the shift in the frequency of the spin resonance in a solid that rotates in the field of a circularly polarized electromagnetic wave. Electron spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are considered. We show that contrary to the case of the rotating LC circuit, the shift in the frequency of the spin resonance has strong dependence on the symmetry of the receiver. The shift due to rotation occurs only when rotational symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape of the body, or by magnetocrystalline anisotropy. General expressions for the resonance …

Edges And Diffractive Effects In Casimir Energies, Daniel N. Kabat, Dimitra Karabali, V P. Nair

Publications and Research

The prototypical Casimir effect arises when a scalar field is confined between parallel Dirichlet boundaries. We study corrections to this when the boundaries themselves have apertures and edges. We consider several geometries: a single plate with a slit in it, perpendicular plates separated by a gap, and two parallel plates, one of which has a long slit of large width, related to the case of one plate being semi-infinite. We develop a general formalism for studying such problems, based on the wavefunctional for the field in the gap between the plates. This formalism leads to a lower dimensional theory defined …

Single Magnetic Molecule Between Conducting Leads: Effect Of Mechanical Rotations, Reem Jaafar, Eugene M. Chudnovsky, Dmitry A. Garanin

Publications and Research

We study spin-rotation effects in a magnetic molecule bridge d between two conducting leads. Dy- namics of the total angular momentum couples spin tunneling to the mechanical rotations. Landau- Zener spin transition produced by the time-dependent magne tic field generates a unique pattern of mechanical oscillations that can be detected by measuring t he electronic tunneling current through the molecule.

Dipolar Ordering In Crystals Of Mn12 Ac, Dmitry A. Garanin

Publications and Research

Ordering in realistic elongated box-shape crystals of the molecular magnet Mn_12 Ac is investigated with the site-resolved mean-field approximation that does not assume a uniform ordering. It is shown that ferromagnetic ordering should not occur in crystals with the aspect ratio up to 12. Instead, for the aspect ratio about 6, the inner and outer regions of the crystal order in different directions, uniformly along its length. Finding ordering temperature by extrapolating the inverse susceptibility curve does not provide a correct T_C.

Dynamical Decompactification And Three Large Dimensions, Brian Greene, Daniel N. Kabat, Stefanos Marnerides

Publications and Research

We study string gas dynamics in the early universe and seek to realize the Brandenberger - Vafa mechanism - a goal that has eluded earlier works - that singles out three or fewer spatial dimensions as the number which grow large cosmologically. Considering wound string interactions in an impact parameter picture, we show that a strong exponential suppression in the interaction rates for d > 3 spatial dimensions reflects the classical argument that string worldsheets generically intersect in at most four spacetime dimensions. This description is appropriate in the early universe if wound strings are heavy - wrapping long cycles - …

Interaction Of A Nanomagnet With A Weak Superconducting Link, Liufei Cai, Eugene M. Chudnovsky

Publications and Research

We study electromagnetic interaction of a nanomagnet with a weak superconducting link. Equations that govern coupled dynamics of the two systems are derived and investigated numerically. We show that the presence of a small magnet in the proximity of a weak link may be detected through Shapiro-like steps caused by the precession of the magnetic moment. Despite very weak magnetic field generated by the weak link, a time-dependent bias voltage applied to the link can initiate a non-linear dynamics of the nanomagnet that leads to the reversal of its magnetic moment. We also consider quantum problem in which a nanomagnet …

Rotational States Of Magnetic Molecules, Eugene M. Chudnovsky, Dmitry A. Garanin

Publications and Research

We study a magnetic molecule that exhibits spin tunneling and is free to rotate about its anisotropy axis. Exact low-energy eigenstates of the molecule that are superpositions of spin and rotational states are obtained. We show that parameter α=2(ℏS)2/(IΔ) determines the ground state of the molecule. Here ℏS is the spin, I is the moment of inertia, and Δ is the tunnel splitting. The magnetic moment of the molecule is zero at α<αc=[1−1/(2S)2]−1 and non-zero at α>αc. At α→∞ the spin of the molecule localizes in one of the directions along the anisotropy axis.