Showing papers on "Scattering length published in 2015"
TL;DR: A systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate is developed, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons.
Abstract: We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Frohlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments.
147 citations
TL;DR: In this article, a general formalism for the scattering of spatially extended Floquet-Bloch waves was developed for the interpretation of ''elastic'' and ''inelastic'' scattering in cases of physical interest.
Abstract: Motivated by recent experimental implementations of artificial gauge fields for gases of cold atoms, we study the scattering properties of particles that are subjected to time-periodic Hamiltonians. Making use of Floquet theory, we focus on translationally invariant situations in which the single-particle dynamics can be described in terms of spatially extended Floquet-Bloch waves. We develop a general formalism for the scattering of these Floquet-Bloch waves. An important role is played by the conservation of Floquet quasienergy, which is defined only up to the addition of integer multiples of $\ensuremath{\hbar}\ensuremath{\omega}$ for a Hamiltonian with period $T=2\ensuremath{\pi}/\ensuremath{\omega}$. We discuss the consequences of this for the interpretation of ``elastic'' and ``inelastic'' scattering in cases of physical interest. We illustrate our general results with applications to the scattering of a single particle in a Floquet-Bloch state from a static potential and the scattering of two bosonic particles in Floquet-Bloch states through their interparticle interaction. We analyze examples of these scattering processes that are closely related to the schemes used to generate artificial gauge fields in cold-atom experiments, through optical dressing of internal states, or through time-periodic modulations of tight-binding lattices. We show that the effects of scattering cannot, in general, be understood by an effective time-independent Hamiltonian, even in the limit $\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\infty}$ of rapid modulation. We discuss the relative sizes of the elastic scattering (required to stabilize many-body phases) and of the inelastic scattering (leading to deleterious heating effects). In particular, we describe how inelastic processes that can cause significant heating in the current experimental setup can be switched off by additional confinement of transverse motion.
111 citations
TL;DR: In this article, the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations are shown to yield a good spectroscopic description of all experimentally relevant isotopes.
Abstract: We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by $\ensuremath{\sim}1{0}^{\ensuremath{-}4}$ compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.
111 citations
TL;DR: In this paper, the nucleon-nucleon system was studied with lattice quantum chromodynamics at a pion mass of $m_\pi\sim 450~{\rm MeV} in three spatial volumes using $n_f=2+1$ flavors of light quarks.
Abstract: Nucleon-nucleon systems are studied with lattice quantum chromodynamics at a pion mass of $$m_\pi\sim 450~{\rm MeV}$$ in three spatial volumes using $n_f=2+1$ flavors of light quarks. At the quark masses employed in this work, the deuteron binding energy is calculated to be $$B_d = 14.4^{+3.2}_{-2.6} ~{\rm MeV}$$, while the dineutron is bound by $$B_{nn} = 12.5^{+3.0}_{-5.0}~{\rm MeV}$$. Over the range of energies that are studied, the S-wave scattering phase shifts calculated in the 1S0 and 3S1-3D1 channels are found to be similar to those in nature, and indicate repulsive short-range components of the interactions, consistent with phenomenological nucleon-nucleon interactions. In both channels, the phase shifts are determined at three energies that lie within the radius of convergence of the effective range expansion, allowing for constraints to be placed on the inverse scattering lengths and effective ranges. Thus, the extracted phase shifts allow for matching to nuclear effective field theories, from which low energy counterterms are extracted and issues of convergence are investigated. As part of the analysis, a detailed investigation of the single hadron sector is performed, enabling a precise determination of the violation of the Gell-Mann–Okubo mass relation.
104 citations
TL;DR: In this article, new integration rules for one-loop scattering equations analogous to those at tree-level were formulated and tested in a number of non-trivial cases for amplitudes in scalar φ 3-theory.
Abstract: We formulate new integration rules for one-loop scattering equations analogous to those at tree-level, and test them in a number of non-trivial cases for amplitudes in scalar φ
3-theory. This formalism greatly facilitates the evaluation of amplitudes in the CHY representation at one-loop order, without the need to explicitly sum over the solutions to the loop-level scattering equations.
97 citations
TL;DR: In this paper, Lambda Lambda correlation measurements in heavy-ion collisions for Au + Au collisions at root s(NN) = 200 GeV using the STAR experiment at the Relativistic Heavy-Ion Collider are presented.
Abstract: We present Lambda Lambda correlation measurements in heavy-ion collisions for Au + Au collisions at root s(NN) = 200 GeV using the STAR experiment at the Relativistic Heavy-Ion Collider. The Lednicky-Lyuboshitz analytical model has been used to fit the data to obtain a source size, a scattering length and an effective range. Implications of the measurement of the Lambda Lambda correlation function and interaction parameters for dihyperon searches are discussed.
87 citations
TL;DR: In this paper, a theoretical framework was developed to investigate the two-body composite structure of a resonance as well as a bound state from its wave function, and the compositeness was defined as a fraction of the contribution of the two body wave function to the normalization of the total wave function.
Abstract: We develop a theoretical framework to investigate the two-body composite structure of a resonance as well as a bound state from its wave function. For this purpose, we introduce both one-body bare states and two-body scattering states, and define the compositeness as a fraction of the contribution of the two-body wave function to the normalization of the total wave function. Writing down explicitly the wave function for a resonance state obtained with a general separable interaction, we formulate the compositeness in terms of the position of the resonance pole, the residue of the scattering amplitude at the pole, and the derivative of the Green function of the free two-body scattering system. At the same time, our formulation provides the elementariness expressed with the resonance properties and the two-body effective interaction, and confirms the sum rule showing that the summation of the compositeness and elementariness gives unity. In this formulation, Weinberg's relation for the scattering length and effective range can be derived in the weak binding limit. The extension to the resonance states is performed with the Gamow vector, and a relativistic formulation is also established. As its applications, we study the compositeness of the $\Lambda (1405)$ resonance and the light scalar and vector mesons described with refined amplitudes in coupled-channel models with interactions up to the next-to-leading order in chiral perturbation theory. We find that $\Lambda (1405)$ and $f_{0}(980)$ are dominated by the $\bar {K} N$ and $K \bar {K}$ composite states, respectively, while the vector mesons $\rho (770)$ and $K^{\ast } (892)$ are elementary. We also briefly discuss the compositeness of $N (1535)$ and $\Lambda (1670)$ obtained in a leading-order chiral unitary approach.
82 citations
TL;DR: In this article, the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases is studied and the authors show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and BCS limits.
Abstract: We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the two-dimensional mean-field theory indicates that the quantum fluctuations are much more pronounced than those in three dimensions. In this work, we show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of two-dimensional Bose gases and determine the ratio of the composite boson scattering length ${a}_{B}$ to the fermion scattering length ${a}_{2\mathrm{D}}$. We find ${a}_{B}\ensuremath{\simeq}0.56{a}_{2\mathrm{D}}$, in good agreement with the exact four-body calculation. We compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.
81 citations
TL;DR: The analysis enables the characterization of the role of singlet scattering in the formation of long-range Rydberg molecules and the determination of an effective singlet s-wave scattering length for low-energy-electron-Cs collisions.
Abstract: We observe the formation of long-range ${\mathrm{Cs}}_{2}$ Rydberg molecules consisting of a Rydberg and a ground-state atom by photoassociation spectroscopy in an ultracold Cs gas near $6{s}_{1/2}(F=3,4)\ensuremath{\rightarrow}n{p}_{3/2}$ resonances ($n=26--34$). The spectra reveal two types of molecular states recently predicted by D. A. Anderson, S. A. Miller, and G. Raithel [Phys. Rev. A 90, 062518 (2014)]: states bound purely by triplet $s$-wave scattering with binding energies ranging from 400 MHz at $n=26$ to 80 MHz at $n=34$, and states bound by mixed singlet-triplet $s$-wave scattering with smaller and $F$-dependent binding energies. The experimental observations are accounted for by an effective Hamiltonian including $s$-wave scattering pseudopotentials, the hyperfine interaction of the ground-state atom, and the spin-orbit interaction of the Rydberg atom. The analysis enables the characterization of the role of singlet scattering in the formation of long-range Rydberg molecules and the determination of an effective singlet $s$-wave scattering length for low-energy-electron--Cs collisions.
79 citations
TL;DR: In this paper, phase shift measurements for neutron matter waves in vacuum and in low pressure Helium using a method originally developed for neutron scattering length measurements in neutron interferometry were performed.
74 citations
TL;DR: In this article, a hard-sphere collision model based on an energy-dependent momentum transport cross section accurately predicts the molecule cooling rate but underestimates the rates of atom heating and loss.
Abstract: We model sympathetic cooling of ground-state CaF molecules by ultracold Li and Rb atoms. The molecules are moving in a microwave trap, while the atoms are trapped magnetically. We calculate the differential elastic cross sections for CaF-Li and CaF-Rb collisions, using model Lennard-Jones potentials adjusted to give typical values for the s-wave scattering length. Together with trajectory calculations, these differential cross sections are used to simulate the cooling of the molecules, the heating of the atoms, and the loss of atoms from the trap. We show that a hard-sphere collision model based on an energy-dependent momentum transport cross section accurately predicts the molecule cooling rate but underestimates the rates of atom heating and loss. Our simulations suggest that Rb is a more effective coolant than Li for ground-state molecules, and that the cooling dynamics is less sensitive to the exact value of the s-wave scattering length when Rb is used. Using realistic experimental parameters, we find that molecules can be sympathetically cooled to 100μK in about 10 s. By applying evaporative cooling to the atoms, the cooling rate can be increased and the final temperature of the molecules can be reduced to 1 μK within 30 s.
TL;DR: In this paper, the authors used the feature that the gravitational Compton scattering amplitude factorizes in terms of Abelian QED amplitudes to evaluate various gravitational Compton processes and showed that the forward scattering cross section for graviton photoproduction has a very peculiar behavior, differing from the standard Thomson and Rutherford cross sections for a Coulomb-like potential.
Abstract: We use the feature that the gravitational Compton scattering amplitude factorizes in terms of Abelian QED amplitudes to evaluate various gravitational Compton processes. We examine both the QED and gravitational Compton scattering from a massive spin-1 system by the use of helicity amplitude methods. In the case of gravitational Compton scattering we show how the massless limit can be used to evaluate the cross section for graviton-photon scattering and discuss the difference between photon interactions and the zero mass spin-1 limit. We show that the forward scattering cross section for graviton photoproduction has a very peculiar behavior, differing from the standard Thomson and Rutherford cross sections for a Coulomb-like potential.
TL;DR: In this paper, the ground state of a dilute Bose gas in a scaling limit where the Gross-Pitaevskii functional emerges was derived based on a combination of Dyson's lemma, the quantum de Finetti theorem and a second moment estimate for ground states of the effective Dyson Hamiltonian.
Abstract: We study the ground state of a dilute Bose gas in a scaling limit where the Gross-Pitaevskii functional emerges. This is a repulsive non-linear Schrodinger functional whose quartic term is proportional to the scattering length of the interparticle interaction potential. We propose a new derivation of this limit problem, with a method that bypasses some of the technical difficulties that previous derivations had to face. The new method is based on a combination of Dyson's lemma, the quantum de Finetti theorem and a second moment estimate for ground states of the effective Dyson Hamiltonian. It applies equally well to the case where magnetic fields or rotation are present.
TL;DR: In this paper, the I = 2 ππ scattering length using Laplacian Heaviside smearing was reduced compared to previous lattice studies, and a detailed investigation of systematic effects such as discretisation effects, volume effects, and pollution of excited and thermal states was performed.
Abstract: We present results for the I = 2 ππ scattering length using N
f
= 2 + 1 + 1 twisted mass lattice QCD for three values of the lattice spacing and a range of pion mass values. Due to the use of Laplacian Heaviside smearing our statistical errors are reduced compared to previous lattice studies. A detailed investigation of systematic effects such as discretisation effects, volume effects, and pollution of excited and thermal states is performed. After extrapolation to the physical point using chiral perturbation theory at NLO we obtain M
π
a
0 = − 0.0442(2)stat(
− 0
+ 4
)sys.
TL;DR: In this paper, the deca-heptuplet partial wave scattering length of dysprosium isotopes was measured using a direct-simulation Monte Carlo method employing the anisotropic differential scattering cross section of dipolar particles.
Abstract: We report the measurement of the deca-heptuplet $s$-partial-wave scattering length $a$ of two bosonic isotopes of the highly magnetic element dysprosium: $a=112(10){a}_{0}$ for $^{162}\mathrm{Dy}$ and $a=92(8){a}_{0}$ for $^{164}\mathrm{Dy}$, where ${a}_{0}$ is the Bohr radius. The scattering lengths are determined by the cross-dimensional relaxation of ultracold gases of these Dy isotopes at temperatures above quantum degeneracy. In this temperature regime, the measured rethermalization dynamics can be compared to simulations of the Boltzmann equation using a direct-simulation Monte Carlo method employing the anisotropic differential scattering cross section of dipolar particles.
TL;DR: In this article, a degenerate Fermi gas was produced with a small number of fermionic atoms in an optical dipole trap, reaching a final temperature of 0.16em.
Abstract: We report on the production of a degenerate Fermi gas of $^{53}\mathrm{Cr}$ atoms, polarized in the state $F=9/2, {m}_{F}=\ensuremath{-}9/2$, by sympathetic cooling with bosonic $S=3,\phantom{\rule{0.16em}{0ex}}{m}_{S}=\ensuremath{-}3 ^{52}\mathrm{Cr}$ atoms. We load in an optical dipole trap $3\ifmmode\times\else\texttimes\fi{}{10}^{4}^{53}\mathrm{Cr}$ atoms with ${10}^{6} ^{52}\mathrm{Cr}$ atoms. Despite the initial small number of fermionic atoms, we reach a final temperature of $T\ensuremath{\simeq}0.6\ifmmode\times\else\texttimes\fi{}{T}_{f}$ (Fermi temperature), with up to ${10}^{3} ^{53}\mathrm{Cr}$ atoms. This surprisingly efficient evaporation stems from an interisotope scattering length $|{a}_{BF}|=80(\ifmmode\pm\else\textpm\fi{}10){a}_{B}$ (Bohr radius) which is small enough to reduce evaporative losses of the fermionic isotope, but large enough to assure thermalization.
TL;DR: The optical theorem is extended and generalized in a cylindrical coordinates system for the case of 2D beams of arbitrary character as opposed to plane waves of infinite extent and reveals the presence of an interference scattering cross-section term describing the interaction between the diffracted Franz waves with the resonance elastic waves.
TL;DR: In this paper, a Galilean-invariant formulation of XEFT is introduced to exploit the fact that mass is very nearly conserved in the transition D*0 --> D0 pi0.
Abstract: XEFT is a low-energy effective field theory for charm mesons and pions that provides a systematically improvable description of the X(3872) resonance. A Galilean-invariant formulation of XEFT is introduced to exploit the fact that mass is very nearly conserved in the transition D*0 --> D0 pi0. The transitions D*0 --> D0 pi0 and X --> D0 D0-bar pi0 are described explicitly in XEFT. The effects of the decay D*0 --> D0 gamma and of short-distance decay modes of the X(3872), such as J/psi --> pi+ pi-, can be taken into account by using complex on-shell renormalization schemes for the D*0 propagator and for the D*0 D0-bar propagator in which the positions of their complex poles are specified. Galilean-invariant XEFT is used to calculate the D*0 D0-bar scattering length to next-to-leading order. Galilean invariance ensures the cancellation of ultraviolet divergences without the need for truncating an expansion in powers of the ratio of the pion and charm meson masses.
TL;DR: In this paper, a generalized optical theorem for beams of arbitrary character in cylindrical coordinates without restriction to the plane wave case of the angles of incidence and scattering is presented, which can be applied to evaluate the extinction efficiency from any object of arbitrary geometry placed on or off the axis of the incident beam.
Abstract: The optical theorem constitutes of the fundamental theorems in optical, acoustical, quantum, and gravitational wave scattering, which relates the extinction cross-section to the forward scattering complex amplitude function of plane waves. In this analysis, a generalized formalism is presented for beams of arbitrary character in cylindrical coordinates without restriction to the plane wave case of the angles of incidence and scattering. Based on the partial-wave series expansion method of cylindrical multipole, analytical expressions for the extinction, absorption, scattering cross-sections and efficiency factors are derived for an object of arbitrary shape. An “interference scattering” term arises in the cross-section (or efficiency), which describes the mutual interference between the diffracted or specularly reflected waves. Examples for plane waves and 2D scalar quasi-Gaussian focused beams are also considered, which illustrate the theory. The generalized optical theorem in cylindrical coordinates can be applied to evaluate the extinction efficiency from any object of arbitrary geometry placed on or off the axis of the incident beam. Applications in the context of wave scattering theory by a single particle or multiple particles would benefit from the results of the present study, in addition to other phenomena such as the radiation force and torque.
TL;DR: In this paper, the authors address the issues of the scattering of massless planar scalar waves by an acoustic black hole in neo-Newtonian hydrodynamics and compute the differential cross section through the use of the partial wave approach.
Abstract: We address the issues of the scattering of massless planar scalar waves by an acoustic black hole in neo-Newtonian hydrodynamics. We then compute the differential cross section through the use of the partial wave approach in the neo-Newtonian theory which is a modification of the usual Newtonian theory that correctly incorporates the effects of pressure. We mainly show that the scattering of planar waves leads to a modified analogue Aharonov-Bohm effect due to a nontrivial response of the parameters defining the equation of state.
TL;DR: In this paper, the virial coefficients, contact parameters, and momentum distribution of a strongly interacting three-dimensional Bose gas were derived by means of a virial expansion up to third order in the fugacity, which takes into account three-body correlations exactly.
Abstract: We compute the virial coefficients, the contact parameters, and the momentum distribution of a strongly interacting three-dimensional Bose gas by means of a virial expansion up to third order in the fugacity, which takes into account three-body correlations exactly. Our results characterize the nondegenerate regime of the interacting Bose gas, where the thermal wavelength is smaller than the interparticle spacing but the scattering length may be arbitrarily large. We observe a rapid variation of the third virial coefficient as the scattering length is tuned across the three-atom and the atom-dimer thresholds. The momentum distribution at unitarity displays a universal high-momentum tail with a log-periodic momentum dependence, which is a direct signature of Efimov physics. We provide a quantitative description of the momentum distribution at high momentum as measured by P. Makotyn et al. [Nat. Phys. 10, 116 (2014)], and our calculations indicate that the lowest trimer state might not be occupied in the experiment. Our results allow for a spectroscopy of Efimov states in the unitary limit.
TL;DR: It is shown that for scatterers with the same average distributions of the scattering potential but different degrees of potential's correlation, the scattered fields with prescribed average intensity distributions can be produced.
Abstract: We explore the possibility of designing correlation functions of a particle’s scattering potential for producing desired scattered intensity distributions, within the validity of the first Born and far-field approximations. It is shown that for scatterers with the same average distributions of the scattering potential (refractive index) but different degrees of potential’s correlation, the scattered fields with prescribed average intensity distributions can be produced. Two examples of such potentials are included: those for flat circular and ring-like scattered intensities, if considered to be a function of the scattering (azimuthal) angle. In both cases the height, width and edge sharpness can be adjusted at will. Production of the novel media is envisioned via the 3D printing or sequences of liquid crystal light modulators.
TL;DR: In this paper, an approach for solving scattering problems, based on two quantum field theory methods, the heat-kernel method and the scattering spectral method, is constructed, which converts a method of calculating heat kernels into a method to solve scattering problems.
Abstract: An approach for solving scattering problems, based on two quantum field theory methods, the heat-kernel method and the scattering spectral method, is constructed. This approach converts a method of calculating heat kernels into a method of solving scattering problems. This allows us to establish a method of scattering problems from a method of heat kernels. As an application, we construct an approach for solving scattering problems based on the covariant perturbation theory of heat-kernel expansions. In order to apply the heat-kernel method to scattering problems, we first calculate the off-diagonal heat-kernel expansion in the frame of covariant perturbation theory. Moreover, as an alternative application of the relation between heat kernels and partial-wave phase shifts presented in this paper, we give an example of how to calculate a global heat kernel from a known scattering phase shift.
TL;DR: In this paper, the energy per particle of symmetric nuclear matter and pure neutron matter was calculated using the microscopic many-body Brueckner-Hartree-Fock (BHF) approach and employing the Argonne V18 (AV18) nucleon-nucleon (NN) potential supplemented with two different three nucleon force models.
Abstract: We calculate the energy per particle of symmetric nuclear matter and pure neutron matter using the microscopic many-body Brueckner-Hartree-Fock (BHF) approach and employing the Argonne V18 (AV18) nucleon-nucleon (NN) potential supplemented with two different three-nucleon force models recently constructed to reproduce the binding energy of $^{3}\mathrm{H},\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ nuclei as well as the neutron-deuteron doublet scattering length. We find that none of these new three-nucleon force models is able to reproduce simultaneously the empirical saturation point of symmetric nuclear matter and the properties of three- and four-nucleon systems.
TL;DR: In this article, a low-momentum expansion up to the fourth order of the quadratic action of the fluctuating pairing field gives an ultraviolent divergent contribution of the Gaussian fluctuations to the grand potential.
Abstract: We study Gaussian fluctuations of the zero-temperature attractive Fermi gas in the 2D BCS-BEC crossover showing that they are crucial to get a reliable equation of state in the BEC regime of composite bosons, bound states of fermionic pairs. A low-momentum expansion up to the fourth order of the quadratic action of the fluctuating pairing field gives an ultraviolent divergent contribution of the Gaussian fluctuations to the grand potential. Performing dimensional regularization we evaluate the effective coupling constant in the beyond-mean-field grand potential. Remarkably, in the BEC regime our grand potential gives exactly the Popov's equation of state of 2D interacting bosons, and allows us to identify the scattering length $a_B$ of the interaction between composite bosons as $a_B=a_F/(2^{1/2}e^{1/4})= 0.551... a_F$, with $a_F$ is the scattering length of fermions. Remarkably, the value from our analytical relationship between the two scattering lengths is in full agreement with that obtained by recent Monte Carlo calculations.
TL;DR: In this article, a detailed discussion of the low-energy proton-deuteron system in pionless effective field theory, considering both the spin-quartet and doublet S-wave channels, is provided.
Abstract: We provide a detailed discussion of the low-energy proton?deuteron system in pionless effective field theory, considering both the spin-quartet and doublet S-wave channels. Extending and amending our previous work on the subject, we calculate the 3He?3H binding energy difference both perturbatively (using properly normalized trinucleon wave functions) and non-perturbatively by resumming all Coulomb diagrams in the doublet channel. Our nonperturbative result agrees well with a calculation that involves the full off-shell Coulomb T-matrix. Carefully examining the cutoff-dependence in the doublet channel, we present numerical evidence for a new three-nucleon counterterm being necessary at next-to-leading order if Coulomb effects are included. Indeed, such a term has recently been identified analytically. We furthermore make a case for a simplified Coulomb power counting that is consistent throughout the bound-state and scattering regimes. Finally, using a ?partially screened? full off-shell Coulomb T-matrix, we investigate the importance of higher-order Coulomb corrections in low-energy quartet-channel scattering.
TL;DR: This work investigates the anisotropy of the Rayleigh scattering in LAB, showing that the resulting Rayleigh scattered length will be significantly shorter than reported before, which will result in a more efficient transmission of photons through the scintillator.
Abstract: Rayleigh scattering poses an intrinsic limit for the transparency of organic liquid scintillators. This work focuses on the Rayleigh scattering length of linear alkylbenzene (LAB), which will be used as the solvent of the liquid scintillator in the central detector of the Jiangmen Underground Neutrino Observatory. We investigate the anisotropy of the Rayleigh scattering in LAB, showing that the resulting Rayleigh scattering length will be significantly shorter than reported before. Given the same overall light attenuation, this will result in a more efficient transmission of photons through the scintillator, increasing the amount of light collected by the photosensors and thereby the energy resolution of the detector.
TL;DR: In this paper, the authors solved the scattering problem for massless chiral fermions impinging on a cylindrical time-dependent potential barrier by solving an effective Dirac-Weyl theory, which is used to model the electron propagation in a monolayer of graphene with harmonically driven quantum dots.
Abstract: Within an effective Dirac-Weyl theory we solve the scattering problem for massless chiral fermions impinging on a cylindrical time-dependent potential barrier. The setup we consider can be used to model the electron propagation in a monolayer of graphene with harmonically driven quantum dots. For static small-sized quantum dots scattering resonances enable particle confinement and interference effects may switch forward scattering on and off. An oscillating dot may cause inelastic scattering by excitation of states with energies shifted by integer multiples of the oscillation frequency, which significantly modifies the scattering characteristics of static dots. Exemplarily the scattering efficiency of a potential barrier with zero bias remains finite in the limit of low particle energies and small potential amplitudes. For an oscillating quantum dot with finite bias, the partial wave resonances at higher energies are smeared out for small frequencies or large oscillation amplitudes, thereby dissolving the quasibound states at the quantum dot.
TL;DR: In this paper, the three-body parameter and structural properties of three helium atoms were analyzed as the s-wave scattering length is tuned artificially, and connections with theoretical and experimental studies of the Efimov scenario as it pertains to cold atom systems are made.
Abstract: Extremely weakly-bound three-boson systems are predicted to exhibit intriguing universal properties such as discrete scale invariance. Motivated by recent experimental studies of the ground and excited helium trimers, this work analyzes the three-body parameter and the structural properties of three helium atoms as the s-wave scattering length is tuned artificially. Connections with theoretical and experimental studies of the Efimov scenario as it pertains to cold atom systems are made.
TL;DR: Pires et al. as discussed by the authors studied the interspecies scattering properties of ultracold Li-C mixtures in their two lowest spin channels in the magnetic field range between 800 and 1000 G.
Abstract: We study the interspecies scattering properties of ultracold Li–Cs mixtures in their two energetically lowest spin channels in the magnetic field range between 800 and 1000 G. Close to two broad Feshbach resonances (FR) we create weakly bound LiCs dimers by radio-frequency association and measure the dependence of their binding energy on the external magnetic field strength. Based on the binding energies and complementary atom loss spectroscopy of three other Li–Cs s-wave FRs we construct precise molecular singlet and triplet electronic ground state potentials using a coupled-channels calculation. We extract the Li–Cs interspecies scattering length as a function of the external field and obtain almost a ten-fold improvement in the precision of the values for the pole positions and widths of the s-wave FRs as compared to our previous work (Pires et al 2014 Phys. Rev. Lett. 112 250404). We discuss implications on the Efimov scenario and the universal geometric scaling for LiCsCs trimers.