Physical Sciences and Mathematics Commons^™

Triple Compton Effect: A Photon Splitting Into Three Upon Collision With A Free Electron, Erik Loetstedt, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

The process in which a photon splits into three after the collision with a free electron (triple Compton effect) is the most basic process for the generation of a high-energy multiparticle entangled state composed out of elementary quanta. The cross section of the process is evaluated in two experimentally realizable situations, one employing gamma photons and stationary electrons, and the other using keV photons and GeV electrons of an x-ray free electron laser. For the first case, our calculation is in agreement with the only available measurement of the differential cross section for the process under study. Our estimates indicate …

Search For Gravitational Waves From Intermediate Mass Binary Black Holes, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450M_⊙ and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 M_⊙, …

First Low-Latency Ligo+Virgo Search For Binary Inspirals And Their Electromagnetic Counterparts, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was …

Disorder Promotes Ferromagnetism: Rounding Of The Quantum Phase Transition In Sr₁₋ₓcaₓruo₃, Laszlo Demko, Sandor Bordacs, Thomas Vojta, David Nozadze, Fawaz Hrahsheh, Christopher Svoboda, Balazs Dora, Hiroyuki Yamada, Masashi Kawasaki, Yoshinori Tokura, Istvan Kezsmarki

Physics Faculty Research & Creative Works

The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr_1-xCa_xRuO₃ is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a magneto-optical technique, we map the magnetic phase diagram in the composition-temperature space. We find …

Dissipation Effects In Random Transverse-Field Ising Chains, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the zero-temperature quantum phase transition in the random transverse-field Ising chain by means of an (asymptotically exact) analytical strong-disorder renormalization-group approach. We find that Ohmic damping destabilizes the infinite-randomness critical point and the associated quantum Griffiths singularities of the dissipationless system. The quantum dynamics of large magnetic clusters freezes completely, which destroys the sharp phase transition by smearing. The effects of sub-Ohmic dissipation are similar and also lead to a smeared transition. In contrast, super-Ohmic damping is an irrelevant perturbation; the critical behavior is thus identical to that of …

Quantum Griffiths Singularities In Ferromagnetic Metals, David Nozadze, Thomas Vojta

Physics Faculty Research & Creative Works

We present a theory of the quantum Griffiths phases associated with the ferromagnetic quantum phase transition in disordered metals. For Ising spin symmetry, we study the dynamics of a single rare region within the variational instanton approach. For Heisenberg symmetry, the dynamics of the rare region is studied using a renormalization group approach. In both cases, the rare region dynamics is even slower than in the usual quantum Griffiths case because the order parameter conservation of an itinerant ferromagnet hampers the relaxation of large magnetic clusters. The resulting quantum Griffiths singularities in ferromagnetic metals are stronger than power laws. For …

Size Effect On The Structural, Magnetic, And Magnetotransport Properties Of Electron Doped Manganite La 0.15ca 0.85mno 3, Rini Thomas, Gangadhar Das, Rajib Mondal, R. Pradheesh, R. N. Mahato, T. Geetha Kumary, R. Nirmala, A. V. Morozkin, J. Lamsal, W. B. Yelon, A. K. Nigam, S. K. Malik

Physics Faculty Research & Creative Works

Nanocrystalline La_0.15Ca_0.85MnO₃ samples of various grain sizes ranging from ∼17 to 42 nm have been prepared by sol-gel technique. Phase purity and composition were verified by room temperature x-ray diffraction and SEM-EDAX analysis. the bulk La_0.15Ca_0.85MnO₃ is known to order antiferromagnetically around 170 K and to undergo a simultaneous crystal structural transition. DC magnetization measurements on 17 nm size La_0.15Ca_0.85MnO₃ show a peak at ∼130 K (T N) in zero-field-cooled (ZFC) state. Field-cooled magnetization bifurcates from ZFC data around 200 K hinting a weak ferromagnetic …

Search For Gravitational Waves From Low Mass Compact Binary Coalescence In Ligo's Sixth Science Run And Virgo's Science Runs 2 And 3, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M_⊙ this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total …

Unconventional Rf Photoresponse From A Superconducting Spiral Resonator, Alexander P. Zhuravel, Cihan Kurter, Alexey V. Ustinov, Steven M. Anlage

Physics Faculty Research & Creative Works

Superconducting thin film resonators employing strip geometries show great promise in rf/microwave applications due to their low loss and compact nature. However, their functionality is limited by nonlinear effects at elevated rf/microwave powers. Here, we show that by using a planar spiral geometry carrying parallel currents in adjacent turns, this limitation can be minimized. We investigate the rf current distributions in spiral resonators implemented with Nb thin films via laser scanning microscopy. The rf current density profile along the width of the individual turns of the resonators reveals an unconventional trend: maximum current in the middle of the structure and …

Electronic Properties Of Layered Multicomponent Wide-Band-Gap Oxides: A Combinatorial Approach, Altynbek Murat, Julia E. Medvedeva

Physics Faculty Research & Creative Works

The structural, electronic, and optical properties of 12 multicomponent oxides with layered structure RAMO ₄, where R3 ⁺ = In or Sc, A3 ⁺ = Al or Ga, and M2 ⁺ = Ca, Cd, Mg, or Zn, are investigated using first-principles density functional approach. The compositional complexity of RAMO ₄ leads to a wide range of band-gap values varying from 2.45 eV for InGaCdO ₄ to 6.29 eV for ScAlMgO ₄ as obtained from our self-consistent screened-exchange local density approximation calculations. Strikingly, despite the different band gaps in the oxide constituents, namely, 2-4 eV in CdO, In ₂O …

Charge Exchange And Ionization In N ⁷ ⁺, N 6 +, C 6 +H(N = 1, 2) Collisions Studied Systematically By Theoretical Approaches, K. Igenbergs, J. Schweinzer, A. Veiter, L. Perneczky, E. Frühwirth, M. Wallerberger, Ronald E. Olson, F. Aumayr

Physics Faculty Research & Creative Works

The introduction of gases like nitrogen or neon for cooling the edge region of magnetically confined fusion plasmas has triggered a renewed interest in state-selective cross sections necessary for plasma diagnostics by means of charge exchange recombination spectroscopy. to improve the quality of spectroscopic data analysis, charge exchange and ionization cross sections for N⁷⁺ + H (n = 1, 2) have been calculated using two different theoretical approaches, namely the atomic-orbital close-coupling method and the classical trajectory Monte Carlo method. Total and state-resolved charge exchange cross sections are presented in detail. in the second part, we compare two collision …

Doubly And Triply Differential Ionization Measurements Using Femtoamp Beams Of Positrons And Electrons, R. D. Dubois

Physics Faculty Research & Creative Works

Experimental methods and techniques being used to generate doubly and triply differential ionization data for positron and electron beams are discussed. It is shown that even for femtoamp, or smaller, beam intensities, highly detailed differential studies can be performed and differences resulting from kinematic effects due to the sign of the projectile can be identified. Examples using 250 eV impact ionization of molecular nitrogen are provided. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Observation Of Spin Glass State In Weakly Ferromagnetic Sr 2fecoo 6 Double Perovskite, R. Pradheesh, Harikrishnan S. Nair, C. M.N. Kumar, Jagat Lamsal, R. Nirmala, P. N. Santhosh, William B. Yelon, S. K. Malik, V. Sankaranarayanan, K. Sethupathi

Physics Faculty Research & Creative Works

A spin glass state is observed in the double perovskite oxide Sr₂FeCoO₆ prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a 5.4609(2) Å and c 7.7113(7) Å. the temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr_{2 …}

Implementation And Testing Of The First Prompt Search For Gravitational Wave Transients With Electromagnetic Counterparts, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations.

Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify …

Bound-Free Pair Production In Ultra-Relativistic Ion Collisions At The Lhc Collider: Analytic Approach To The Total And Differential Cross Sections, Anton N. Artemyev, Ulrich D. Jentschura, Valery G. Serbo, Andrey S. Surzhykov

Physics Faculty Research & Creative Works

A theoretical investigation of the bound-free electron-positron pair production in relativistic heavy ion collisions is presented. Special attention is paid to the positrons emitted under large angles with respect to the beam direction. The measurement of these positrons in coincidence with the down-charged ions is in principle feasible by LHC experiments. In order to provide reliable estimates for such measurements, we employ the equivalent photon approximation together with the Sauter approach and derive simple analytic expressions for the differential pair-production cross section, which compare favorably to the results of available numerical calculations. Based on the analytic expressions, detailed calculations are …

Switching Nonlinearity In A Superconductor-Enhanced Metamaterial, Cihan Kurter, Philippe Tassin, Alexander P. Zhuravel, Lei Zhang, Thomas Koschny, Alexey V. Ustinov, Costas M. Soukoulis, Steven M. Anlage

Physics Faculty Research & Creative Works

We demonstrate a nonlinear metamaterial that can be switched between low and high transmission by controlling the power level of the incident beam. The origin of this nonlinear response is the superconducting Nb thin film employed in the metamaterial structure. We show that with moderate RF power of about 22 dBm it is possible to quench the superconducting state as a result of extremely strong current densities at the corners of the metamaterial's split-ring resonators. We measure a transmission contrast of 10 dB and a change in group delay of 70 ns between the low and high power states.

Low-Energy Electron-Impact Ionization Of Argon: Three-Dimensional Cross Section, Xueguang Ren, Thomas Pfluger, Joachim Hermann Ullrich, Oleg I. Zatsarinny, Klaus Bartschat, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Low-energy (E ₀ = 70.8 eV) electron-impact single ionization of a 3p electron in argon has been studied experimentally and theoretically. Our measurements are performed using the so-called reaction microscope technique, which can cover nearly a full 4π solid angle for the emission of a secondary electron with energy below 15 eV and projectile scattering angles ranging from -8° to -30°. The measured cross sections are internormalized across all scattering angles and ejected energies. Several theoretical models were employed to predict the triple-differential cross sections (TDCSs). They include a standard distorted-wave Born approximation (DWBA), a modified version to account for …

Low Energy (E,2e) Measurements Of Ch⁴ And Neon In The Perpendicular Plane, Kate L. Nixon, Andrew James Murray, Hari Chaluvadi, Sadek Amami, Don H. Madison, Chuangang Ning

Physics Faculty Research & Creative Works

Low energy experimental and theoretical triple differential cross sections for the highest occupied molecular orbital of methane (1t₂) and for the 2p atomic orbital of neon are presented and compared. These targets are iso-electronic, each containing 10 electrons and the chosen orbital within each target has p-electron character. Observation of the differences and similarities of the cross sections for these two species hence gives insight into the different scattering mechanisms occurring for atomic and molecular targets. The experiments used perpendicular, symmetric kinematics with outgoing electron energies between 1.5 eV and 30 eV for CH₄ and 2.5 eV …

State-Selective Electron Transfer And Ionization In Collisions Of Highly Charged Ions With Ground-State Na(3s) And Laser-Excited Na *(3p), I. Blank, Sebastian Otranto, C. Meinema, Ronald E. Olson, R. Hoekstra

Physics Faculty Research & Creative Works

Single electron transfer and ionization in collisions of N⁵⁺ and Ne⁸⁺ with ground state Na(3s) and laser excited Na *(3p) are investigated both experimentally and theoretically at collision energies from 1 to 10 keV/amu, which includes the classical orbital velocity of the valence electron. State-selective partial cross sections are obtained using recoil-ion momentum spectroscopy in combination with a magneto-optically cooled Na atom target. a strong dependence of the cross sections on the collision energy is observed. in general, both the relative magnitude and the energy dependence are found to be in good agreement with classical-trajectory Monte Carlo calculations. …

Localizability Of Tachyonic Particles And Neutrinoless Double Beta Decay, Ulrich D. Jentschura, Benedikt J. Wundt

Physics Faculty Research & Creative Works

The quantum field theory of superluminal (tachyonic) particles is plagued by a number of problems, which include the Lorentz non-invariance of the vacuum state, the ambiguous separation of the field operator into creation and annihilation operators under Lorentz transformations, and the necessity of a complex reinterpretation principle for quantum processes. Another unsolved question concerns the treatment of subluminal components of a tachyonic wave packet in the field-theoretical formalism, and the calculation of the time-ordered propagator. After a brief discussion on related problems, we conclude that rather painful choices have to be made in order to incorporate tachyonic spin-1/2 particles into …

Artificially Disordered Birefringent Optical Fibers, Sumudu Herath, N. P. Puente, Elena I. Chaikina, Alexey Yamilov

Physics Faculty Research & Creative Works

We develop and experimentally verify a theory of evolution of polarization in artificially-disordered multi-mode optical fibers. Starting with a microscopic model of photo-induced index change, we obtain the first and second order statistics of the dielectric tensor in a Ge-doped fiber, where a volume disorder is intentionally inscribed via UV radiation transmitted through a diffuser. A hybrid coupled-power & coupled-mode theory is developed to describe the transient process of de-polarization of light launched into such a fiber. After certain characteristic distance, the power is predicted to be equally distributed over all co-propagating modes of the fiber regardless of their polarization. …

Enhancement Of Blackbody Friction Due To The Finite Lifetime Of Atomic Levels, G. Łach, M. Dekieviet, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

The thermal friction force acting on an atom moving relative to a thermal photon bath is known to be proportional to an integral over the imaginary part of the frequency-dependent atomic (dipole) polarizability. using a numerical approach, we find that blackbody friction on atoms either in dilute environments or in hot ovens is larger than previously thought by orders of magnitude. This enhancement is due to far off-resonant driving of transitions by low-frequency thermal radiation. at typical temperatures, the blackbody radiation maximum lies far below the atomic transition wavelengths. Surprisingly, due to the finite lifetime of atomic levels, which gives …

Multiscale Perturbative Approach To Su(2)-Higgs Classical Dynamics: Stability Of Nonlinear Plane Waves And Bounds Of The Higgs Field Mass, V. Achilleos, F. K. Diakonos, D. J. Frantzeskakis, Garyfallia C. Katsimiga, X. N. Maintas, C. E. Tsagkarakis, A. Tsapalis

Physics Faculty Research & Creative Works

We study the classical dynamics of SU(2)-Higgs field theory using multiple-scale perturbation theory. In the spontaneously broken phase, assuming small perturbations of the Higgs field around its vacuum expectation value, we derive a nonlinear Schrödinger equation and study the stability of its nonlinear plane wave solutions. The latter turn out to be stable only if the Higgs amplitude is an order of magnitude smaller than that of the gauge field. In this case, the Higgs field mass possesses some bounds which may be relevant to the search for the Higgs particle at ongoing experiments. © 2012 American Physical Society.

Differential Cross Sections For Single Ionization Of H₂ By 75kev Proton Impact, Uttam Chowdhury, Michael Schulz, Don H. Madison

Physics Faculty Research & Creative Works

We have calculated Triply differential cross sections (TDCS) and doubly differential cross sections (DDCS) for single ionization of H₂ by 75 keV proton impact using the molecular 3 body distorted wave Eikonal initial state (M3DW-EIS) approach. Previously published measured DDCS-P (differential in the projectile scattering angle and integrated over the ejected electron angles) found pronounced structures at relatively large angles which were interpreted as an interference resulting from the two-centered potential of the molecule.

Intensity Dependence Of Multiple Orbital Contributions And Shape Resonance In High-Order Harmonic Generation Of Aligned N₂ Molecules, Cheng Jin, Julien B. Bertrand, R. R. Lucchese, H .J. Worner, Paul B. Corkum, D. M. Villeneuve, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We report measurements and theoretical simulations of high-order harmonic generation (HHG) in aligned N₂ molecules using a 1200-nm intense laser field when the generating pulse is perpendicular to the aligning one. With increasing laser intensity, the minimum in the HHG spectra first shifts its position and then disappears. Theoretical simulations including the macroscopic propagation effects in the medium reproduce these observations and the disappearance of the minimum is attributed to the additional contribution of HHG from inner orbitals. We also predict that the well-known shape resonance in the photoionization spectra of N₂ should exist in the HHG spectra. It is …

All-Sky Search For Periodic Gravitational Waves In The Full S5 Ligo Data, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We report on an all-sky search for periodic gravitational waves in the frequency band 50-800Hz and with the frequency time derivative in the range of 0 through -6 x 10^-9Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10x increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150Hz our upper limit on …

Strongly Enhanced Backward Emission Of Electrons In Transfer And Ionization, Michael Schulz, Xincheng Wang, M. Gundmundsson, Katharina R. Schneider, Aditya H. Kelkar, Alexander B. Voitkiv, B. Najjari, Markus S. Schoffler, Lothar Ph H H Schmidt, Reinhard Dorner, Joachim Hermann Ullrich, Robert Moshammer, Daniel Fischer

Physics Faculty Research & Creative Works

We studied three-dimensional angular distributions and longitudinal momentum spectra of electrons ejected in transfer plus ionization (TI), i.e., the ejection of one and the capture of a second target electron, for ion-helium collisions. We observe a pronounced structure strongly focused opposite to the projectile beam direction, which we associate with a new correlated TI mechanism proposed recently. This process contributes significantly to the total cross sections over a broad range of perturbations η, even at η as large as 0.5, where uncorrelated TI mechanisms were thought to be dominant.

Experimental And Theoretical Investigation Of The Triple Differential Cross Section For Electron Impact Ionization Of Pyrimidine Molecules, J. D. Builth-Williams, Susan M. Bellm, Darryl B. Jones, Hari Chaluvadi, Don H. Madison, Chuangang Ning, B. Lohmann, Michael J. Brunger

Physics Faculty Research & Creative Works

Cross-section data for electron impact induced ionization of bio-molecules are important for modelling the deposition of energy within a biological medium and for gaining knowledge of electron driven processes at the molecular level. Triply differential cross sections have been measured for the electron impact ionization of the outer valence 7b ₂ and 10a ₁ orbitals of pyrimidine, using the (e, 2e) technique. The measurements have been performed with coplanar asymmetric kinematics, at an incident electron energy of 250 eV and ejected electron energy of 20 eV, for scattered electron angles of -5°, -10°, and -15°. The ejected electron angular range …

Effect Of Projectile Coherence On Atomic Fragmentation Processes, Michael Schulz, Kisra N. Egodapitiya, Sachin D. Sharma, Aaron C. Laforge, Robert Moshammer, A. A. Hasan, Don H. Madison

Physics Faculty Research & Creative Works

We demonstrate that the projectile coherence can have a major impact on atomic fragmentation processes. This has been overlooked for decades in formal scattering theory and may explain puzzling discrepancies between theoretical and experimental fully differential cross sections for single ionization.

Comparison Of Experiment And Theory For Electron Impact Ionization Of Isoelectronic Atoms And Molecules, Hari Chaluvadi, Kate L. Nixon, Sadek M. Amami, Andrew James Murray, Don H. Madison

Physics Faculty Research & Creative Works

Experimental and Theoretical Triply Differential Cross sections will be presented for low energy electron impact ionization of Ne, CH₄, and NH₃. The collision mechanisms responsible for the various structures found in the cross sections will be discussed.