Search

Recently we have published a paper [Irgaziev, Phys. Rev. C 91, 024002 (2015)] where the S-matrix pole method (SMP), which is only valid for resonances, has been developed to derive an explicit expression for the asymptotic normalization coefficient (ANC) and is applied to the low-energy resonant states of nucleon + α and α + 12C systems. The SMP results are compared with the effective-range expansion method (EFE) results. In the present paper the SMP and EFE plus the Padé approximation are applied to study the excited 2+ resonant states of 8Be. A contradiction is found between descriptions of the experimental phase shift data for αα scattering and of the 8Be resonant energy for 2+ state. Using the EFE method, we also calculate the ANC for the 8Be ground 0+ state with a very small width. This ANC agrees well with the value calculated using the known analytical expression for narrow resonances. In addition, for the α + 12C states 1- and 3- the SMP results are compared with the Padé approximation results. We find that the Padé approximation improves a resonance width description compared with the EFE results. The EFE method is also used to calculate the ANCs for the bound 16O ground 0+ state and for the excited 1- and 2+ levels, which are situated near the threshold of α + 12C channel. [ABSTRACT FROM AUTHOR]

Soft limits of a massless S matrix are known to reflect the symmetries of the theory. In particular, for theories with Goldstone bosons, the double-soft limit of scalars reveals the coset structure of the vacuum manifold. In this Letter, we propose that such universal double-soft behavior is not only true for scalars, but also for spin-1/2 particles in four dimensions and fermions in three dimensions. We first consider the Akulov-Volkov theory and demonstrate that the double-soft limit of Goldstinos yields the supersymmetry algebra. More surprisingly, we also find that amplitudes in 4≤N≤8 supergravity theories in four dimensions as well as N=16 supergravity in three dimensions behave universally in the double-soft-fermion limit, analogous to the scalar ones. The validity of the new soft theorems at loop level is also studied. The results for supergravity are beyond what is implied by supersymmetry Ward identities and may impose nontrivial constraints on the possible counterterms for supergravity theories. [ABSTRACT FROM AUTHOR]

We study the thermalization of gluons far from thermal equilibrium in relativistic kinetic theory. The initial distribution of gluons is assumed to resemble that in the early stage of ultrarelativistic heavy ion collisions. Only elastic scatterings in static, nonexpanding gluonic matter are considered. At first we show that the occurrence of condensation in the limit of vanishing particle mass requires a general constraint for the scattering matrix element. Then the thermalization of gluons with Bose-Einstein condensation is demonstrated in a transport calculation. We see a continuously increasing overpopulation of low energy gluons, followed by a decrease to the equilibrium distribution, when the condensation occurs. The times of the completion of the gluon condensation and of the entropy production are calculated. These times scale inversely with the energy density. [ABSTRACT FROM AUTHOR]

Using the evolutionary model-independent S-matrix approach, we show that a simultaneous correct description of the pictures of nuclear rainbow, prerainbow, and anomalous large-angle scattering (ALAS) in the 4He-40Ca elastic scattering can be achieved with help of the S-matrix moduli and the real nuclear phases exhibiting smooth monotonic dependencies on angular momentum, while the quantum deflection functions have a form characteristic of the nuclear rainbow case. The special role of the surface partial waves in the formation of ALAS is revealed. [ABSTRACT FROM AUTHOR]

Asymptotic normalization coefficients (ANCs) are fundamental nuclear constants playing an important role in nuclear physics and astrophysics. We derive a new useful relationship between ANCs of the Gamow radial wave function and the renormalized (due to the Coulomb interaction) Coulomb-nuclear partial scattering amplitude. We use an analytical approximation in the form of a series for the nonresonant part of the phase shift which can be analytically continued to the point of an isolated resonance pole in the complex plane of the momentum. Earlier, this method which we call the S-matrix pole method was used by us to find the resonance pole energy. We find the corresponding fitting parameters for the 5He, 5Li, and 16O concrete resonance states. Additionally, based on the theory of the effective range, we calculate the parameters of the p3/2 and p1/2 resonance states of the nuclei 5He and 5Li and compare them with the results obtained by the S-matrix pole method. ANC values are found which can be used to calculate the reaction rate through the 16O resonances which lie slightly above the threshold for the α12C channel. [ABSTRACT FROM AUTHOR]

The use of finite harmonic oscillator spaces in many-body calculations introduces both infrared (IR) and ultraviolet (UV) errors. The IR effects are well approximated by imposing a hard-wall boundary condition at a properly identified radius Leff. We show that duality of the oscillator implies that the UV effects are equally well described by imposing a sharp momentum cutoff at a momentum Aeff complementary to Leff. By considering two-body systems with separable potentials, we show that the UV energy corrections depend on details of the potential, in contrast to the IR energy corrections, which depend only on the 5-matrix. An adaptation of the separable treatment to more general interactions is developed and applied to model potentials as well as to the deuteron with realistic potentials. The previous success with a simple phenomenological form for the UV error is also explained. Possibilities for controlled extrapolations for A > 2 based on scaling arguments are discussed. [ABSTRACT FROM AUTHOR]

Recently, a new approach for solving the three-body problem for (d,p) reactions in the Coulomb-distorted basis in momentum space was proposed. Important input quantities for such calculations are the scattering matrix elements for proton- (neutron-) nucleus scattering. We present a generalization of the the Ernst-Shakin-Thaler scheme in which a momentum space separable representation of proton-nucleus scattering matrix elements in the Coulomb basis can be calculated. The success of this method is demonstrated by comparing S-matrix elements and cross sections for proton scattering from 12C, 48Ca, and 208Pb with the corresponding coordinate space calculations. [ABSTRACT FROM AUTHOR]

We investigate the subgap bulk transport through short and wide superconducting hybrid structures based on HgTe quantum wells (QWs). We show that the differential conductance of a normal-metal-insulatorsuperconductor (NIS) proximity structure behaves in a qualitatively different way with respect to the topological phase of the HgTe QW. We compare the differential conductance for the NIS structure within the wave-matching method based on the Bogoliubov-de Gennes equation and the matrix method based on the normal-state scattering matrix and find that the two models agree for highly doped N and S contacts. We also show that the effect of a possible Rashba spin-orbit interaction on the differential conductance can be significant for weakly doped N and S contacts. Our findings should be important in samples with a large aspect ratio where bulk contributions in transport are dominant. [ABSTRACT FROM AUTHOR]

We construct a scattering matrix formulation for the topological classification of one-dimensional superconductors with effective time-reversal symmetry in the presence of interactions. For an isolated system, Fidkowski and Kitaev have shown that such systems have a ℤ8 topological classification. We here show that these systems have a unitary scattering matrix at zero temperature when weakly coupled to a normal-metal lead, with a topological index given by the trace of the Andreev-reflection matrix, trrhe. With interactions, trrhe generically takes on the finite set of values 0, ±1, ±2, ±3, and ±4. We show that the two topologically equivalent phases with trrhe=±4 support emergent many-body end states, which we identify to be a topologically protected Kondo-like resonance. The path in phase space that connects these equivalent phases crosses a non-Fermi-liquid fixed point where a multiple-channel Kondo effect develops. Our results connect the topological index to transport properties, thereby highlighting the experimental signatures of interacting topological phases in one dimension. [ABSTRACT FROM AUTHOR]

We analyze the full-counting statistics of the electric heat current flowing in a two-terminal quantum conductor whose temperature is probed by a third electrode ("probe electrode"). In particular we demonstrate that the cumulant-generating function obeys the fluctuation theorem in the presence of a constant magnetic field. The analysis is based on the scattering matrix of the three-terminal junction (comprising the two electronic terminals and the probe electrode), and a separation of time scales: it is assumed that the rapid charge transfer across the conductor and the rapid relaxation of the electrons inside the probe electrode give rise to much slower energy fluctuations in the latter. This separation allows for a stochastic treatment of the probe dynamics, and the reduction of the three-terminal setup to an effective two-terminal one. Expressions for the lowest nonlinear transport coefficients, e.g., the linear-response heat-current noise and the second nonlinear thermal conductance, are obtained and explicitly shown to preserve the symmetry of the fluctuation theorem for the two-terminal conductor. The derivation of our expressions, which is based on the transport coefficients of the three-terminal system explicitly satisfying the fluctuation theorem, requires full calculations of vertex corrections. [ABSTRACT FROM AUTHOR]

I present the Floquet scattering matrix theory of low-frequency heat fluctuations in driven quantum-coherent conductors in the linear response regime and beyond. The Floquet theory elucidates the use of the Callen-Welton fluctuation-dissipation theorem for a description of heat fluctuations in a multiterminal case. The intrinsic fluctuations of energy of dynamically excited electrons are identified as the fundamental source of heat noise not revealed by the electrical noise. The role of backscattering in the increase of heat noise above the level defined by the Callen-Welton theorem is highlighted. The exception is the case when a conductor is driven by a Lorentzian voltage pulse with quantized flux. The heat noise in this case falls down to the level pertaining to a linear response regime. [ABSTRACT FROM AUTHOR]

We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kuho-Greenwood formula, show that in disordered graphene superlattices the strength of multiple scattering phenomena can strongly depend on the transport measurement geometry. This eventually yields the coexistence of a ballistic waveguide and a highly resistive channel (Anderson insulator) in the same two-dimensional platform, evidenced by a σyy/σxx ratio varying over several orders of magnitude, and suggesting the possibility of building graphene electronic circuits based on the unique properties of chiral massless Dirac fermions in graphene. [ABSTRACT FROM AUTHOR]

The role of disorder in the field of three-dimensional time-reversal-invariant topological insulators has become an active field of research recently. However, the computation of ℤ2 invariants for large, disordered systems still poses a considerable challenge. In this paper, we apply and extend a recently proposed method based on the scattering matrix approach, which allows the study of large systems at reasonable computational effort with few-channel leads. By computing the ℤ2 invariant directly for the disordered topological Anderson insulator, we unambiguously identify the topological nature of this phase without resorting to its connection with the clean case. We are able to efficiently compute the ℤ2 phase diagram in the mass-disorder plane. The topological phase boundaries are found to be well described by the self-consistent Born approximation, both for vanishing and finite chemical potentials. [ABSTRACT FROM AUTHOR]

We present a Floquet scattering theory of electron waiting time distributions in periodically driven quantum conductors. We employ a second-quantized formulation that allows us to relate the waiting time distribution to the Floquet scattering matrix of the system. As an application we evaluate the electron waiting times for a quantum point contact, modulating either the applied voltage (external driving) or the transmission probability (internal driving) periodically in time. Lorentzian-shaped voltage pulses are of particular interest as they lead to the emission of clean single-particle excitations as recently demonstrated experimentally. The distributions of waiting times provide us with a detailed characterization of the dynamical properties of the quantum-coherent conductor in addition to what can be obtained from the shot noise or the full counting statistics. [ABSTRACT FROM AUTHOR]

Poles of partial wave scattering matrices in hadron spectroscopy have recently been established as a sole link between experiment and QCD theories and models. Karlsruhe-Helsinki (KH) partial wave analyses have been "above the line" in the Review of Particle Physics (RPP) for over three decades. The RPP compiles Breit-Wigner (BW) parameters from local BW fits, but give only a limited number of pole positions using speed plots (SP). In the KH method only Mandelstam analyticity is used as a theoretical constraint, so these partial wave solutions are as model independent as possible. They are a valuable source of information. It is unsatisfactory that BW parameters given in the RPP have been obtained from the KH80 solution, while pole parameters have been obtained from the KA84 version. To remedy this, we have used a newly developed Laurent + Pietarinen expansion method to obtain pole positions for all partial waves for KH80 and KA84 solutions. We show that differences from pole parameters are, with a few exceptions, negligible for most partial waves. We give a full set of pole parameters for both solutions. [ABSTRACT FROM AUTHOR]

The article discusses the study which builds the non-Abelian topological order for topological band models using entanglement entropy measurement. The study involves non-Abelian Moore-Read and Read-Rezayi states' quasiparticle statistics on lattice models with bosonic particles. The study identifies multiple independent minimal entangled states (MESs) in torus's ground state manifolds in which a modular S matrix from MESs was extracted and demonstrates Fibonacci quasiparticle.

The optical-model potential for the n+9Be reaction is obtained by two methods. The first method is from a modification and generalization of previous work [Bonaccorso and Bertsch, Phys. Rev. C 63, 044604 (2001)] and the second is from a dispersive-optical-model fit. The two potentials and also quantities derived from the S matrices used to calculate neutron knockout cross sections are compared. [ABSTRACT FROM AUTHOR]

In this paper, the implication of the extreme large Nc limit for nucleon-nucleon cross section is examined. Starting from the Nc scaling of the S-matrix elements, a relation between the total inelastic and total cross sections is derived for the regime in which the momenta are much larger than the QCD scale. A conceptual complication arises from the fact that there is a tower of baryons, such as the ∆, with mass splittings from the nucleon which go to zero at large Nc. Since these baryons are stable at large Nc, the meaning of elasticity must be modified. Processes which only transform nucleons to these baryons are considered elastic; processes in which at least one additional meson is produced are considered inelastic. It is shown that in the extreme large Nc limit, the total inelastic cross section is exactly one eighth of the total cross section. In contrast, in the physical world of Nc = 3, the total cross section for high-energy nucleon-nucleon scattering is dominated by inelastic processes. [ABSTRACT FROM AUTHOR]

Two single-particle sources coupled in series to a chiral electronic waveguide can serve as a probabilistic source of two-particle excitations with tunable properties. The second-order correlation function, characterizing the state of emitted electrons in space-time, is expressed in terms of the Floquet scattering matrix of a source. It is shown that the Fourier transform of the correlation function, characterizing the emitted state in energy space, can be accessed with the help of an energy resolved shot-noise measurement. The two-electron state emitted adiabatically is discussed in detail. In particular, the two-electron wave function is represented via two different sets of single-particle wave functions accessible experimentally. [ABSTRACT FROM AUTHOR]

It is shown that universal transport statistics in the ensembles of scattering matrices with the symmetry index β ∈ {1 ,2,4} can be found from a simple microscopic model. A stochastic Riccati equation for the reflection matrix in this model is mapped exactly to the Dorokhov-Mello-Pereyra-Kumar equation for all βs. The map is used to obtain transport statistics in a quasi-one-dimensional disordered conductor in a wide range of its parameters from ballistic to localizations regime. The conductance statistics, shot noise suppression. and transmission channel density are calculated and compared with available analytical results. Deviation from the universal statistics is also discussed. [ABSTRACT FROM AUTHOR]

We derive expressions for both parallel and perpendicular components of spin transfer torque (STT) in magnetic tunnel junctions (MTJs), which have several important advantages over the currently available expressions: First they are derived in a more realistic approximation, resulting in excellent agreement with exact results even in the presence of resonant tunneling. Second, we show that they can be expressed in terms of the scattering matrix elements, which gives them a clear physical interpretation. Third, they are given entirely in terms of collinear quantities, which are readily available in existing transport codes. We use these expressions to investigate STT behavior in MTJs with asymmetric barriers at finite bias. The results show that lowering the barrier height in the bulk does not qualitatively change the behavior of STT. The absolute STT increases on account of the overall increase of the barrier transparency; however, the STT efficiency remains in the same range. At the same time, modifications of the interfaces can qualitatively change STT behavior. Thus, interface engineering can be used to control the bias dependence of STT and optimize the performance of STT-based devices. [ABSTRACT FROM AUTHOR]

We present results of a new multichannel partial-wave analysis for K N scattering in the center-of-mass (c.m.) energy range from 1480 to 2100 MeV. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters are generally in good agreement with predictions of the Koniuk-Isgur quark model. [ABSTRACT FROM AUTHOR]

We present an analytic random matrix theory for the effect of incomplete channel control on the measured statistical properties of the scattering matrix of a disordered multiple-scattering medium. When the fraction of the controlled input channels, m1, and output channels, m2, is decreased from unity, the density of the transmission eigenvalues is shown to evolve from the bimodal distribution describing coherent diffusion, to the distribution characteristic of uncorrelated Gaussian random matrices, with a rapid loss of access to the open eigenchannels. The loss of correlation is also reflected in an increase in the information capacity per channel of the medium. Our results have strong implications for optical and microwave experiments on diffusive scattering media. [ABSTRACT FROM AUTHOR]

Scattering is an important phenomenon which is observed in systems ranging from the micro- to macroscale. In the context of nuclear reaction theory, the Heidelberg approach was proposed and later demonstrated to be applicable to many chaotic scattering systems. To model the universal properties, stochasticity is introduced to the scattering matrix on the level of the Hamiltonian by using random matrices. A long-standing problem was the computation of the distribution of the off-diagonal scattering- matrix elements. We report here an exact solution to this problem and present analytical results for systems with preserved and with violated time-reversal invariance. Our derivation is based on a new variant of the supersymmetry method. We also validate our results with scattering data obtained from experiments with microwave billiards. [ABSTRACT FROM AUTHOR]

We study numerically scattering and transport statistical properties of tight-binding random networks characterized by the number of nodes N and the average connectivity α. We use a scattering approach to electronic transport and concentrate on the case of a small number of single-channel attached leads. We observe a smooth crossover from insulating to metallic behavior in the average scattering matrix elements (|Smn|²), the conductance probability distribution w(T), the average conductance (T), the shot noise power P, and the elastic enhancement factor F by varying a from small (α → 0) to large (α → 1 ) values. We also show that all these quantities are invariant for fixed ξ = αN. Moreover, we proposes a heuristic and universal relation between (|Smn|²), (T) and P and the disorder parameter ξ. [ABSTRACT FROM AUTHOR]

Motivated by the recent advances in studying Majorana states in nanowires under conditions of the superconducting proximity effect, we address the correspondence between the common topological transition in an infinite system and a topological transition of another type that manifests itself in the positions of the poles of the scattering matrices. We establish a universal dependence of the pole positions in the vicinity of the common transition on the parameter controlling the transition, and discuss the manifestations of the pole transitions in the differential conductance. [ABSTRACT FROM AUTHOR]

We investigate the Fano-Kondo interplay in an Aharonov-Bohm ring with an embedded noninteracting quantum dot and a Coulomb interacting quantum dot. Using a slave-boson mean-field approximation we diagonalize the Hamiltonian via scattering matrix theory and derive the conductance in the form of a Fano expression, which depends on the mean-field parameters. We predict that in the Kondo regime the magnetic field leads to a gapped energy level spectrum due to hybridization of the noninteracting QD state and the Kondo state, and can quantum-mechanically alter the electron's path preference. We demonstrate that an abrupt symmetry change in the Fano resonance, as seen experimentally, could be a consequence of an underlying Kondo channel. [ABSTRACT FROM AUTHOR]

We study the statistical properties of the impedance matrix (related to the scattering matrix) describing the input-output properties of waves in cavities in which ray trajectories that are regular and chaotic coexist (i.e., "mixed" systems). The impedance can be written as a summation over eigenmodes where the eigenmodes can typically be classified as either regular or chaotic. By appropriate characterizations of regular and chaotic contributions, we obtain statistical predictions for the impedance. We then test these predictions by comparison with numerical calculations for a specific cavity shape, obtaining good agreemen [ABSTRACT FROM AUTHOR]

We show that the Dirac-Born-Infeld conformal galileons, derived from the world-volume theory of a 3-brane moving in an anti–de Sitter bulk, admit a background, stable under quantum corrections, which violates the null energy condition. The perturbations around this background are stable and propagate subluminally. Unlike other known examples of null energy condition violation, such as ghost condensation and conformal galileons, this theory also admits a stable, Poincaré-invariant vacuum. The 2 → 2 amplitude satisfies standard analyticity conditions. The full S matrix is likely not analytic, however, since perturbations around deformations of the Poincaré invariant vacuum propagate superluminally. [ABSTRACT FROM AUTHOR]

We use entanglement entropy signatures to establish non-Abelian topological order in projected Chern-insulator wave functions. The simplest instance is obtained by Gutzwiller projecting a filled band with Chern number C=2, whose wave function may also be viewed as the square of the Slater determinant of a band insulator. We demonstrate that this wave function is captured by the SU(2)2 Chern-Simons theory coupled to fermions. This is established most persuasively by calculating the modular S-matrix from the candidate ground-state wave functions, following a recent entanglement-entropy-based approach. This directly demonstrates the peculiar non-Abelian braiding statistics of Majorana fermion quasiparticles in this state. We also provide microscopic evidence for the field theoretic generalization, that the Nth power of a Chern number C Slater determinant realizes the topological order of the SU(N)C Chern-Simons theory coupled to fermions, by studying the SU(2)3 (Read-Rezayi-type state) and the SU(3)2 wave functions. An advantage of our projected Chern-insulator wave functions is the relative ease with which physical properties, such as entanglement entropy and modular S-matrix, can be numerically calculated using Monte Carlo techniques. [ABSTRACT FROM AUTHOR]

The Verbaarschot-Weidenmüller-Zirnbauer (VWZ) model is believed to correctly represent the correlations of two S-matrix elements for an open quantum chaotic system, but the solution has considerable complexity and is presently only accessed numerically. Here a procedure is developed to deduce its features over the full range of the parameter space in a transparent and simple analytical form preserving accuracy to a considerable degree. The bulk of the VWZ correlations are described by the Gorin-Seligman expression for the two-amplitude correlations of the Ericson-Gorin-Seligman model. The structure of the remaining correction factors for correlation functions is discussed with special emphasis of the rôle of the level correlation hole both for inelastic and elastic correlations. [ABSTRACT FROM AUTHOR]

For thermoelectric transport in the presence of a magnetic field that breaks time-reversal symmetry, a strong bound on the Onsager coefficients is derived within a general setup using three terminals. Asymmetric Onsager coefficients lead to a maximum efficiency substantially smaller than the Carnot efficiency reaching only ηC/4 in the limit of strong asymmetry. Related bounds are derived for efficiency at maximum power, which can become larger than the Curzon-Ahlborn value ηC/2, and for a cooling device. Our approach reveals that in the presence of reversible currents the standard analysis based on the positivity of entropy production is incomplete without considering the role of current conservation explicitly. [ABSTRACT FROM AUTHOR]

Given a microscopic lattice Hamiltonian for a topologically ordered phase, we propose a numerical approach to characterize its emergent anyon model and, in a chiral phase, also its gapless edge theory. First, a tensor network representation of a complete, orthonormal set of ground states on a cylinder of infinite length and finite width is obtained through numerical optimization. Each of these ground states is argued to have a different anyonic flux threading through the cylinder. Then a quasiorthogonal basis on the torus is produced by chopping off and reconnecting the tensor network representation on the cylinder. From these two bases, and by using a number of previous results, most notably the recent proposal of Y. Zhang et al. [ Phys. Rev. B 85 235151 (2012)] to extract the modular U and S matrices, we obtain (i) a complete list of anyon types i, together with (ii) their quantum dimensions di and total quantum dimension D, (iii) their fusion rules Nijk, (iv) their mutual statistics, as encoded in the off-diagonal entries Sij of S, (v) their self-statistics or topological spins ϑi, (vi) the topological central charge c of the anyon model, and, in a chiral phase (vii) the low energy spectrum of each sector of the boundary conformal field theory. As a concrete application, we study the hard-core boson Haldane model by using the two-dimensional density matrix renormalization group. A thorough characterization of its universal bulk and edge properties unambiguously shows that it realizes a v=1/2 bosonic fractional quantum Hall state. [ABSTRACT FROM AUTHOR]

We calculate the S-matrix correlation function for chaotic scattering on quantum graphs and show that it agrees with that of random-matrix theory. We also calculate all higher S-matrix correlation functions in the Ericson regime. These, too, agree with random-matrix theory results as far as the latter are known. We conjecture that our results give a universal description of chaotic scattering. [ABSTRACT FROM AUTHOR]

We present results of a new multichannel partial-wave analysis for πN scattering in the c.m. energy range 1080 to 2100 MeV. This work explicitly includes ηN and KΛ channels and the single pion photoproduction channel. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters so obtained are compared to predictions of quark models. [ABSTRACT FROM AUTHOR]