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Articles **1** - **16** of ** 16**

## Full-Text Articles in Physical Sciences and Mathematics

Magic Wavelength For The Hydrogen 1s-2s Transition: Contribution Of The Continuum And The Reduced-Mass Correction, Chandra M. Adhikari, A. Kawasaki, Ulrich D. Jentschura

#### Magic Wavelength For The Hydrogen 1s-2s Transition: Contribution Of The Continuum And The Reduced-Mass Correction, Chandra M. Adhikari, A. Kawasaki, Ulrich D. Jentschura

*Physics Faculty Research & Creative Works*

Recently, we studied the magic wavelength for the atomic hydrogen 1S-2S transition [A. Kawasaki, Phys. Rev. A 92, 042507 (2015)PLRAAN1050-294710.1103/PhysRevA.92.042507]. An explicit summation over virtual atomic states of the discrete part of the hydrogen spectrum was performed to evaluate the atomic polarizability. In this paper, we supplement the contribution of the continuum part of the spectrum and add the reduced-mass correction. The magic wavelength, at which the lowest-order ac Stark shifts of the 1S and 2S states are equal, is found to be 514.6 nm. The ac Stark shift at the magic wavelength is ...

Impact Of Massive Neutrinos On The Nonlinear Matter Power Spectrum, Shun Saito, Masahiro Takada, Atsushi Taruya

#### Impact Of Massive Neutrinos On The Nonlinear Matter Power Spectrum, Shun Saito, Masahiro Takada, Atsushi Taruya

*Physics Faculty Research & Creative Works*

We present the first attempt to analytically study the nonlinear matter power spectrum for a mixed dark matter model containing neutrinos of total mass ~0.1eV, based on cosmological perturbation theory. The suppression in the power spectrum amplitudes due to massive neutrinos is enhanced in the weakly nonlinear regime. We demonstrate that, thanks to this enhanced effect, the use of such a nonlinear model may enable a precision of σ(_{mÎ½,tot}) ~ 0. 07eV in constraining the total neutrino mass for the planned galaxy redshift survey, a factor of 2 improvement compared to the linear regime.

Black Hole Particle Emission In Higher-Dimensional Spacetimes, Vitor Cardoso, Marco Cavaglia, Leonardo Gualtieri

#### Black Hole Particle Emission In Higher-Dimensional Spacetimes, Vitor Cardoso, Marco Cavaglia, Leonardo Gualtieri

*Physics Faculty Research & Creative Works*

In models with extra dimensions, a black hole evaporates both in the bulk and on the visible brane, where standard model fields live. The exact emissivities of each particle species are needed to determine how the black hole decay proceeds. We compute and discuss the absorption cross sections, the relative emissivities, and the total power output of all known fields in the evaporation phase. Graviton emissivity is highly enhanced as the spacetime dimensionality increases. Therefore, a black hole loses a significant fraction of its mass in the bulk. This result has important consequences for the phenomenology of black holes in ...

Exotic Versus Conventional Scaling And Universality In A Disordered Bilayer Quantum Heisenberg Antiferromagnet, Rastko Sknepnek, Thomas Vojta, Matthias Vojta

#### Exotic Versus Conventional Scaling And Universality In A Disordered Bilayer Quantum Heisenberg Antiferromagnet, Rastko Sknepnek, Thomas Vojta, Matthias Vojta

*Physics Faculty Research & Creative Works*

We present Monte Carlo simulations of a two-dimensional bilayer quantum Heisenberg antiferromagnet with random dimer dilution. In contrast with exotic scaling scenarios found in other random quantum systems, the quantum phase transition in this system is characterized by a finite-disorder fixed point with power-law scaling. After accounting for corrections to scaling, with a leading irrelevant exponent of ω ≈ 0.48, we find universal critical exponents z = 1.310(6) and ν = 1.16(3). We discuss the consequences of these findings and suggest new experiments.

Disorder-Induced Rounding Of Certain Quantum Phase Transitions, Thomas Vojta

#### Disorder-Induced Rounding Of Certain Quantum Phase Transitions, Thomas Vojta

*Physics Faculty Research & Creative Works*

We study the influence of quenched disorder on quantum phase transitions in systems with overdamped dynamics. For Ising order-parameter symmetry disorder destroys the sharp phase transition by rounding because a static order parameter can develop on rare spatial regions. This leads to an exponential dependence of the order parameter on the coupling constant. At finite temperatures the static order on the rare regions is destroyed. This restores the phase transition and leads to a double exponential relation between critical temperature and coupling strength. We discuss the behavior based on Lifshitz-tail arguments and illustrate the results by simulations of a model ...

Temperature Dependence Of Droplet Nucleation In A Yukawa Fluid, Jinsong Li, Gerald Wilemski

#### Temperature Dependence Of Droplet Nucleation In A Yukawa Fluid, Jinsong Li, Gerald Wilemski

*Physics Faculty Research & Creative Works*

We have studied the temperature dependence of gas-to-liquid nucleation in Yukawa fluids with gradient theory and density functional theory. Each of these nonclassical theories exhibits a weaker (i.e., better) temperature dependence than classical nucleation theory. At fixed temperature, the reversible work to form a critical nucleus found from gradient theory approaches the value given by density functional theory as the supersaturation increases. At high temperatures, the two theories remain quite close over a wide range of vapor densities. As the temperature is reduced, the difference between the two theories increases with decreasing vapor density. Compared to the classical theory ...

Electron-Impact Excitation From The (4p⁵5s) Metastable States Of Krypton, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani

#### Electron-Impact Excitation From The (4p⁵5s) Metastable States Of Krypton, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani

*Physics Faculty Research & Creative Works*

Theoretical results from multistate semirelativistic Breit-Pauli R-matrix calculations and two first-order distorted-wave calculations are presented for electron-impact excitation of krypton from the (4p^{5}5s) J = 0,2 metastable states to the (4p^{5}5s) and (4p^{5}5p) manifolds. Except for a few cases, in which the method to account for relativistic effects becomes surprisingly critical, fair overall agreement between the predictions from the various theoretical models is achieved for intermediate and high energies. However, significant discrepancies remain with the few available experimental data.

Strong Enhancement Of Superconducting T_{C} In Ferromagnetic Phases, Theodore R. Kirkpatrick, Dietrich Belitz, Thomas Vojta, Rajesh S. Narayanan

#### Strong Enhancement Of Superconducting TC In Ferromagnetic Phases, Theodore R. Kirkpatrick, Dietrich Belitz, Thomas Vojta, Rajesh S. Narayanan

*Physics Faculty Research & Creative Works*

It is shown that the critical temperature for spin-triplet, p-wave superconductivity mediated by spin fluctuations is generically much higher in a Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling of the magnons to the longitudinal magnetic susceptibility. Together with the tendency of the low-temperature ferromagnetic transition in very clean Heisenberg magnets to be of first order, this qualitatively explains the phase diagram recently observed in UGe_{2}.

Transport Anomalies And Marginal Fermi-Liquid Effects At A Quantum Critical Point, Dietrich Belitz, Theodore R. Kirkpatrick, Rajesh S. Narayanan, Thomas Vojta

#### Transport Anomalies And Marginal Fermi-Liquid Effects At A Quantum Critical Point, Dietrich Belitz, Theodore R. Kirkpatrick, Rajesh S. Narayanan, Thomas Vojta

*Physics Faculty Research & Creative Works*

The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependencies that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.

Ionization Of Hydrogen Atoms By Fast Electrons, Sindu P. Jones, Don H. Madison

#### Ionization Of Hydrogen Atoms By Fast Electrons, Sindu P. Jones, Don H. Madison

*Physics Faculty Research & Creative Works*

We study ionization of atomic hydrogen by fast electrons using asymptotically correct two-center wave functions to describe the scattering system both initially and finally. For the final state, we employ the well-known product wave function of Redmond, which treats all three two-body Coulomb interactions exactly, albeit independently. This "3C" wave function is the leading term of the exact scattering wave function, regardless of how *slow* the three particles are, if any two particles have large relative *separation* [Y.E. Kim and A.L. Zubarev, Phys. Rev. A 56, 521 (1997)]. Here we extend the analysis of Qiu *et al.* [Phys ...

Short-Pulse Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

#### Short-Pulse Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

*Physics Faculty Research & Creative Works*

Atoms in doubly excited states above the first ionization limit can decay via autoionization in which an electron is emitted leaving an ion, or by photoemission which leaves the atom in a singly excited state. In this paper, it is demonstrated that interaction between the atoms and a laser pulse that is short compared to the autoionization lifetime can lead to large enhancement of the photoemission process by stimulating the atoms to emit a photon. Since the resultant singly excited atoms do not autoionize, this process can be viewed as an enhancement of the stabilization of the doubly excited atoms ...

Direct Measurement Of Oscillations Between Degenerate Two-Electron Bound-State Configurations In A Rapidly Autoionizing System, Heider N. Ereifej, J. Greg Story

#### Direct Measurement Of Oscillations Between Degenerate Two-Electron Bound-State Configurations In A Rapidly Autoionizing System, Heider N. Ereifej, J. Greg Story

*Physics Faculty Research & Creative Works*

In this paper we report a direct observation of the oscillation between bound-state configurations in a rapidly autoionizing system. Calcium atoms were excited to a pure 4p_{3/2}nd two-electron configuration using a 500-fsec laser pulse. The initial 4p_{3/2}nd doubly excited state is energy degenerate with the 4p_{1/2}n'd states and several continuum channels. Because of the short-pulse excitation, the initial state of the atom is not an energy eigenstate, but a nonstationary wave packet. As a result, oscillations between the two bound configurations were produced. These oscillations were measured by scanning the ...

Do Interactions Increase Or Reduce The Conductance Of Disordered Electrons? It Depends!, Thomas Vojta, Frank Epperlein, Michael Schreiber

#### Do Interactions Increase Or Reduce The Conductance Of Disordered Electrons? It Depends!, Thomas Vojta, Frank Epperlein, Michael Schreiber

*Physics Faculty Research & Creative Works*

We investigate the influence of electron-electron interactions on the conductance of two-dimensional disordered spinless electrons. We present an efficient numerical method based on diagonalization in a truncated basis of Hartree-Fock states to determine with high accuracy the low-energy properties in the entire parameter space. We find that weak interactions increase the dc conductance in the strongly localized regime while they decrease the dc conductance for weak disorder. Strong interactions always decrease the conductance. We also study the localization of single-particle excitations at the Fermi energy which turns out to be only weakly influenced by the interactions.

Chaotic Behavior And Damage Spreading In The Glauber Ising Model: A Master Equation Approach, Thomas Vojta

#### Chaotic Behavior And Damage Spreading In The Glauber Ising Model: A Master Equation Approach, Thomas Vojta

*Physics Faculty Research & Creative Works*

We investigate the sensitivity of the time evolution of a kinetic Ising model with Glauber dynamics against the initial conditions. To do so we apply the "damage spreading" method, i.e., we study the simultaneous evolution of two identical systems subjected to the same thermal noise. We derive a master equation for the joint probability distribution of the two systems. We then solve this master equation within an effective-field approximation which goes beyond the usual mean-field approximation by retaining the fluctuations though in a quite simplistic manner. The resulting effective-field theory is applied to different physical situations. It is used ...

Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris

#### Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris

*Physics Faculty Research & Creative Works*

Time-of-flight measurements on a wide variety of molecularly-doped polymers reveal carrier mobilities that exhibit an exponential dependence on the square root of the applied electric field. Recent attempts to explain the observed field dependence have focused on the role played by spatial and energetic disorder. It as also been conjectured that the charge-dipole interactions often identified as the source of energetic disorder could be of sufficient range to lead to correlations in the energies of neighboring hopping sites. We have analytically explored the effect of such correlations on high field carrier transport in random potentials, and discuss how particular features ...

Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

#### Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

*Physics Faculty Research & Creative Works*

When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the two-photon ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensity-tuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the ...