Search Results (12)

We reconsider the problem of neutrino-pair bremsstrahlung emission originating from the electromagnetic collisions of charged particles in nucleonic ($\mathrm{n}\mathrm{p}\mathrm{e}\mathrm{\mu }$) neutron star cores. Two limiting cases are considered: (i) protons in the normal state and (ii) protons in the superconducting state. In both cases, the dominant contribution to the bremsstrahlung emissivity $Q_{\mathrm{Br}}^{\mathrm{em}}$ comes from the transverse part of in-medium electromagnetic interactions. For non-superconducting matter, we obtain an unusual $Q_{\mathrm{Br}}^{\mathrm{em}}\propto T^{23/3}$ temperature dependence due to the dynamical character of plasma screening in the transverse channel, but these are considerably smaller values of $Q_{\mathrm{Br}}^{\mathrm{em}}$ than in previous studies, rendering the considered process unimportant in practice. In contrast, for superconducting and superfluid matter, the neutrino emission processes involving nucleons are suppressed and $Q_{\mathrm{Br}}^{\mathrm{em}}$ due to lepton collisions provides the residual contribution to the neutrino emissivity of neutron star core matter. In the superconducting case, the plasma screening becomes static and the standard $Q_{\mathrm{Br}}^{\mathrm{em}}\propto T^8$ temperature scaling is restored. Simple analytical expressions for $Q_{\mathrm{Br}}^{\mathrm{em}}$ in both limiting cases are provided. Full article

We consider the macroscopic motion of the normal component of superfluid ³He-A in global thermodynamic equilibrium within the context of the Zubarev statistical operator method. We formulate the corresponding effective theory in the language of the functional integral. The effective Lagrangian comprising macroscopic motion of fermionic excitations is calculated explicitly for the emergent relativistic fermions of the superfluid ³He-A phase immersed in a non-trivial bosonic background due to a space- and time-dependent matrix-valued vierbein featuring nonzero torsion as well as the Nieh–Yan anomaly. We do not consider the dynamics of the superfluid component itself and thereby its backreaction effects due to normal component macroscopic flow. It is treated as an external background within which the emergent relativistic fermions of the normal component move. The matrix-valued vierbein formulation comprises an additional two-dimensional internal spin space for the two axially charged Weyl fermions living at the Fermi points, which may be replaced by one featuring a Dirac fermion doublet with a real-valued vierbein, an axial Abelian gauge field, and a spin connection gauge field mixing the Dirac and internal spin spaces. We carry out this change of description in detail and determine the constraints on the superfluid background as well as the the normal component motion as determined from the Zubarev statistical operator formalism in global thermodynamic equilibrium. As an application of the developed theory, we consider macroscopic rotation around the axis of pure integer mass vortices. The corresponding thermodynamic quantities of the normal component are analyzed. Our formulation incorporates both superfluid background flow and macroscopic motion flow of the normal component and thereby enables an analysis of their interrelation. Full article

We discuss the derivation of the electrodynamics of superconductors coupled to the electromagnetic field from a Lorentz-invariant bosonic model of Cooper pairs. Our results are obtained at zero temperature where, according to the third law of thermodynamics, the entropy of the system is zero. In the nonrelativistic limit, we obtain a Galilei-invariant superconducting system, which differs with respect to the familiar Schrödinger-like one. From this point of view, there are similarities with the Pauli equation of fermions, which is derived from the Dirac equation in the nonrelativistic limit and has a spin-magnetic field term in contrast with the Schrödinger equation. One of the peculiar effects of our model is the decay of a static electric field inside a superconductor exactly with the London penetration length. In addition, our theory predicts a modified D’Alembert equation for the massive electromagnetic field also in the case of nonrelativistic superconducting matter. We emphasize the role of the Nambu–Goldstone phase field, which is crucial to obtain the collective modes of the superconducting matter field. In the special case of a nonrelativistic neutral superfluid, we find a gapless Bogoliubov-like spectrum, while for the charged superfluid we obtain a dispersion relation that is gapped by the plasma frequency. Full article

We show that the GENERIC model for relativistic heat conduction is a multifluid of Carter; this allows one to compute the multifluid constitutive relations directly from the GENERIC formalism. As a quick application, we prove that in the limit of infinite heat conductivity, GENERIC heat conduction reduces to the relativistic two-fluid model for superfluidity. This surprising “crossover” is a consequence of relativistic causality: if diffusion happens too fast, all the diffusing charge cumulates on the surface of the light cone, and it eventually travels at the speed of light like a wave. Our analysis is non-perturbative and carried out in a fully non-linear regime. Full article

We investigate theoretically the momentum-dependent frequency and damping of low-lying collective excitations of superconductors and charged superfluids in the BCS–BEC crossover regime. The study is based on the Gaussian pair-and-density fluctuation method for the propagator of Gaussian fluctuations of the pair and density fields. Eigenfrequencies and damping rates are determined in a mutually consistent nonperturbative way as complex poles of the fluctuation propagator. Particular attention is paid to new features with respect to preceding theoretical studies, which were devoted to collective excitations of superconductors in the far BCS regime. We find that at a sufficiently strong coupling, new branches of collective excitations appear, which manifest different behavior as functions of the momentum and the temperature. Full article

We present path integral molecular dynamics (PIMD) calculations of an electron transfer from a heliophobic Cs${}_2$ dimer in its (${}^3{\Sigma }_{\mathrm{u}}$) state, located on the surface of a He droplet, to a heliophilic, fully immersed C${}_{60}$ molecule. Supported by electron ionization mass spectroscopy measurements (Renzler et al., J. Chem. Phys.2016, 145, 181101), this spatially quenched reaction was characterized as a harpoon-type or long-range electron transfer in a previous high-level ab initio study (de Lara-Castells et al., J. Phys. Chem. Lett.2017, 8, 4284). To go beyond the static approach, classical and quantum PIMD simulations are performed at 2 K, slightly below the critical temperature for helium superfluidity (2.172 K). Calculations are executed in the NVT ensemble as well as the NVE ensemble to provide insights into real-time dynamics. A droplet size of 2090 atoms is assumed to study the impact of spatial hindrance on reactivity. By changing the number of beads in the PIMD simulations, the impact of quantization can be studied in greater detail and without an implicit assumption of superfluidity. We find that the reaction probability increases with higher levels of quantization. Our findings confirm earlier, static predictions of a rotational motion of the Cs${}_2$ dimer upon reacting with the fullerene, involving a substantial displacement of helium. However, it also raises the new question of whether the interacting species are driven out-of-equilibrium after impurity uptake, since reactivity is strongly quenched if a full thermal equilibration is assumed. More generally, our work points towards a novel mechanism for long-range electron transfer through an interplay between nuclear quantum delocalization within the confining medium and delocalized electronic dispersion forces acting on the two reactants. Full article

The I-Love-Q relations are approximate equation-of-state independent relations that connect the moment of inertia, the spin-induced quadrupole moment, and the tidal deformability of neutron stars. In this paper, we study the I-Love-Q relations for superfluid neutron stars for a general relativistic two-fluid model: one fluid being the neutron superfluid and the other a conglomerate of all charged components. We study to what extent the two-fluid dynamics might affect the robustness of the I-Love-Q relations by using a simple two-component polytropic model and a relativistic mean field model with entrainment for the equation-of-state. Our results depend crucially on the spin ratio ${\Omega }_{\mathrm{n}}/{\Omega }_{\mathrm{p}}$ between the angular velocities of the neutron superfluid and the normal component. We find that the I-Love-Q relations can still be satisfied to high accuracy for superfluid neutron stars as long as the two fluids are nearly co-rotating ${\Omega }_{\mathrm{n}}/{\Omega }_{\mathrm{p}}\approx 1$. However, the deviations from the I-Love-Q relations increase as the spin ratio deviates from unity. In particular, the deviation of the Q-Love relation can be as large as $O(10\%)$ if ${\Omega }_{\mathrm{n}}/{\Omega }_{\mathrm{p}}$ differ from unity by a few tens of percent. As ${\Omega }_{\mathrm{n}}/{\Omega }_{\mathrm{p}}\approx 1$ is expected for realistic neutron stars, our results suggest that the two-fluid dynamics should not affect the accuracy of any gravitational waveform models for neutron star binaries that employ the relation to connect the spin-induced quadrupole moment and the tidal deformability. Full article

It is shown, that $(4+1)$—and $(3+1+1)$—reductions of the geodetic equations in 5D theory with scalar field $\phi =\sqrt{-G_{55}}$ and out of the 5D optics inevitably lead to the new concept of the Lorentz-type relativistic mass ${\hat{m}}_0$ of the 5D test particle. Due to the imposition of the $x^5$—cylindricity condition, one can obtain an integral of the 5D particle’s motion along $x^5$; it gives its electric charge. Thus, one can obtain an exact expression for ${\widehat{m}}_0$. In this expression ${\widehat{m}}_0$ depends on the field $\phi$ through an electric charge, so there is not probably any need for a scalar charge in Nature at all. Furthermore, one can compactly express the ${\widehat{m}}_0$ through the mass angle ${\chi }_n$ and additionally hypothesize about the possible complex structure of ${\widehat{m}}_0$. It soundly leads one to the deeper understanding of the quantum properties of the matter. All of these conceptions also turn one to the idea that this mass ${\widehat{m}}_0$ may contribute to the recently discovered in the Universe dark matter and dark energy and also be one of the possible reasons for the Universe’s expansion. The next suggestive result in the 5D theory is connected with the $(4+1)$—reduction of the 5D Ricci identities. It leads one to certain connections between the 4D physicogeometrical values and permits one to obtain the first pair of Maxwell equations with the non-zero soliton-type r.h.s. and establishes the connection with the second pair of them. It subsequently leads one to the idea about the magnetic monopole’s existence in the early Universe. It is shown, that this non-zero r.h.s. vanishes together with the imposition of the $x^5$—cylindricity condition. The peculiarity of this process permits one to hypothesize soundly about the existence of the topological second-order transition in the Universe, which leads one to the superfluid state and possibly accelerates its expansion. Full article

We review a modern differential geometric description of fluid isentropic motion and features of it including diffeomorphism group structure, modelling the related dynamics, as well as its compatibility with the quasi-stationary thermodynamical constraints. We analyze the adiabatic liquid dynamics, within which, following the general approach, the nature of the related Poissonian structure on the fluid motion phase space as a semidirect Banach groups product, and a natural reduction of the canonical symplectic structure on its cotangent space to the classical Lie-Poisson bracket on the adjoint space to the corresponding semidirect Lie algebras product are explained in detail. We also present a modification of the Hamiltonian analysis in case of a flow governed by isothermal liquid dynamics. We study the differential-geometric structure of isentropic magneto-hydrodynamic superfluid phase space and its related motion within the Hamiltonian analysis and related invariant theory. In particular, we construct an infinite hierarchy of different kinds of integral magneto-hydrodynamic invariants, generalizing those previously constructed in the literature, and analyzing their differential-geometric origins. A charged liquid dynamics on the phase space invariant with respect to an abelian gauge group transformation is also investigated, and some generalizations of the canonical Lie-Poisson type bracket is presented. Full article

For large isospin asymmetries, perturbation theory predicts the quantum chromodynamic (QCD) ground state to be a superfluid phase of u and $\overline{d}$ Cooper pairs. This phase, which is denoted as the Bardeen-Cooper-Schrieffer (BCS) phase, is expected to be smoothly connected to the standard phase with Bose-Einstein condensation (BEC) of charged pions at ${\mu }_I\ge m_{\pi }/2$ by an analytic crossover. A first hint for the existence of the BCS phase, which is likely characterised by the presence of both deconfinement and charged pion condensation, comes from the lattice observation that the deconfinement crossover smoothly penetrates into the BEC phase. To further scrutinize the existence of the BCS phase, in this article we investigate the complex spectrum of the massive Dirac operator in 2+1-flavor QCD at nonzero temperature and isospin chemical potential. The spectral density near the origin is related to the BCS gap via a generalization of the Banks-Casher relation to the case of complex Dirac eigenvalues (derived for the zero-temperature, high-density limits of QCD at nonzero isospin chemical potential). Full article

We used an electronic phase separation approach to interpret the scaling between the low-temperature superfluid density average ${\rho }_{\mathrm{sc}}\left(0\right)$ and the superconducting critical temperature $T_{\mathrm{c}}$ on overdoped La ${}_{2-x}$ Sr ${}_x$ CuO ${}_4$ films. Guided by the observed nematic and incommensurate charge ordering (CO), we performed simulations with a free energy that reproduces charge domains with wavelength ${\lambda }_{CO}$ and provides a scale to local superconducting interactions. Under these conditions a complex order parameter with amplitude ${\mathsf{\Delta }}_d\left(r_i\right)$ and phase $\theta \left(r_i\right)$ may develop at a domain i. We assumed that these domains are coupled by Josephson energy $E_{\mathrm{J}}\left(r_{ij}\right)$ , proportional to the local superfluid density ${\rho }_{\mathrm{sc}}\left(r_{ij}\right)$ . Long-range order occured when the average $E_{\mathrm{J}}\left(T_{\mathrm{c}}\right)$ is $\sim k_{\mathrm{B}}{T}_{\mathrm{c}}$ . The linear ${\rho }_{sc}\left(0\right)$ vs. $T_{\mathrm{c}}$ relation was satisfied whenever CO was present, even with almost vanishing charge amplitudes. Full article

Searches for permanent electric dipole moments (EDMs) of fundamental particles, atoms and molecules are promising experiments to constrain and potentially reveal beyond Standard Model (SM) physics. A non-zero EDM is a direct manifestation of time-reversal (T) violation, and, equivalently, violation of the combined operation of charge-conjugation (C) and parity inversion (P). Identifying new sources of CP violation can help to solve fundamental puzzles of the SM, e.g., the observed baryon-asymmetry in the Universe. Theoretical predictions for magnitudes of EDMs in the SM are many orders of magnitude below current experimental limits. However, many theories beyond the SM require larger EDMs. Experimental results, especially when combined in a global analysis, impose strong constraints on CP violating model parameters. Including an overview of EDM searches, I will focus on the future neutron EDM experiment at TRIUMF (Vancouver). For this effort, the TUCAN (TRIUMF Ultra Cold Advanced Neutron source) collaboration is aiming to build a strong, world leading source of ultra cold neutrons (UCN) based on a unique combination of a spallation target and a superfluid helium UCN converter. Another focus will be the search for an EDM of the diamagnetic atom ${}^{129}$ Xe using a ${}^3$ He comagnetometer and SQUID detection. The HeXeEDM collaboration has taken EDM data in 2017 and 2018 in the magnetically shielded room (BMSR-2) at PTB Berlin. Full article