Damping of sound waves in superfluid nucleon-hyperon matter of neutron stars

We consider sound waves in superfluid nucleon-hyperon matter of massive neutron-star cores. We calculate and analyze the speeds of sound modes and their damping times due to the shear viscosity and non-equilibrium weak processes of particle transformations. For that, we employ the dissipative relativistic hydrodynamics of a superfluid nucleon-hyperon mixture, formulated recently [M.E. Gusakov and E.M. Kantor, Phys. Rev. D78, 083006 (2008)]. We demonstrate that the damping times of sound modes calculated using this hydrodynamics and the ordinary (nonsuperfluid) one, can differ from each other by several orders of magnitude.Comment: 15 pages, 5 figures, Phys. Rev. D accepte

Observability of HOFNARs with SRG/eROSITA

Neutron stars can appear as sources of different nature. In this paper we address observability of a hypothetical class of neutron stars -- HOt and Fast Non Accreting Rotators, HOFNARs. These objects are heated due to the r-mode instability. With surface temperatures $\sim 10^6$~K they are expected to be thermal soft X-ray emitters. We perform a population synthesis modeling of HOFNARs to predict the number of potentially detectable sources in the eROSITA all-sky survey. For surface temperatures $\sim 10^6$~K we obtain $\sim 500$ sources above the detection limit 0.01~cts~s$^{-1}$ and $\sim 100$ easier identifiable sources with $>0.1$~cts~s$^{-1}$. Temperatures $\gtrsim 1.2\times 10^6$~K start to be in contradiction with non-detection of HOFNARs by ROSAT. Only for $T\lesssim 5\times 10^5$~K numbers predicted for eROSITA turn out to be so low that identification does not look possible. We conclude that eROSITA has good chances to discover HOFNARs, if they exist. Non-detection will put very stringent limits on the properties of this type of neutron stars.Comment: 17 pages, submitted to Univers

Spectral Properties of Single Crystals of Synthetic Diamond

The half-width of the spectrum of Raman scattering (RS) of the first order of a diamond single crystal grown in a nickel-free system containing nitrogen getters is identical to all growth sectors (1.69 ± 0.02 cm−1). The sectorial inhomogeneity is not reflected in the transmission spectra and birefringence of this crystal. The nitrogen concentration is 4⋅1017 cm−3. For different growth sectors of the diamond crystal grown in the Ni–Fe–C system, the half-width of the Raman line varies from 1.74 to 2.08 cm−1, differences in the transmission spectra and birefringence are observed, and photoluminescence is revealed. The concentration of nitrogen in the growth sectors {001} is 1.6⋅1019 cm−3, the content of nickel is estimated to be at a level of 1019 cm−3, and the content of nitrogen in the {111} sectors is 4⋅1019 cm−3

Bulk viscosity of superfluid hyperon stars

We calculated bulk viscosity due to non-equilibrium weak processes in superfluid nucleon-hyperon matter of neutron stars. For that, the dissipative relativistic hydrodynamics, formulated in paper [1] for superfluid mixtures, was extended to the case when both nucleons and hyperons are superfluid. It was demonstrated that in the most general case (when neutrons, protons, Lambda, and Sigma^{-} hyperons are superfluid), non-equilibrium weak processes generate sixteen bulk viscosity coefficients, with only three of them being independent. In addition, we corrected an inaccuracy in a widely used formula for the bulk viscosity of non-superfluid nucleon-hyperon matter.Comment: 22 pages, 2 figure

Bulk viscosity of superfluid neutron stars

The hydrodynamics, describing dynamical effects in superfluid neutron stars, essentially differs from the standard one-fluid hydrodynamics. In particular, we have four bulk viscosity coefficients in the theory instead of one. In this paper we calculate these coefficients, for the first time, assuming they are due to non-equilibrium beta-processes (such as modified or direct Urca process). The results of our analysis are used to estimate characteristic damping times of sound waves in superfluid neutron stars. It is demonstrated that all four bulk viscosity coefficients lead to comparable dissipation of sound waves and should be considered on the same footing.Comment: 11 pages, 1 figure, this version with some minor stylistic changes is published in Phys. Rev.

Recurrent vulvovaginal candidiasis during COVID-19 pandemic: medical algorithm

The review article presents data on the prevalence of candidiasis of various localization against the history of coronavirus infection (COVID-19). The predisposing factors for the development and recurrence of candidiasis in patients after therapy for coronavirus infection have been analysed. Candida is one of the most common pathogens in intensive care units (ICUs), affecting 6 to 10% of patients, and some studies have reported an increasing trend in the prevalence of candidemia. The literature data that we analysed showed that the most common types of fungal infection among patients with a severe course of COVID-19 were C. albicans, then C. auris, C. glabrata, C. parapsilosis, C. tropicalis, S. cerevisiae, C. krusei and Rhodotorula spp. Candida non-albicans species, in particular C. glabrata, C. auris, were the most common causes of death. The previous treatment regimens for patients with COVID-19 included antibiotics, but at present time corticosteroids are more often used, which have an immunosuppressive effect and, accordingly, predispose to the development of candidiasis. The epithelial injury caused by SARS-CoV-2 also enables Candida to attach to the basement membrane, subsequently triggering the development of mucosal candidiasis. As the systemic and local candidiasis are conditioned by common immune mechanisms that are affected by coronavirus infection, vulvovaginal candidiasis (VVC) may recur during COVID-19 therapy. The timely diagnosis and treatment of fungal infections in patients who underwent COVID-19 are crucial for achieving a positive clinical outcome. The article provides an algorithm for the management of patients with recurrent VVC, the principles of action of antifungal drugs, their acceptability and efficacy

Transport in holographic superfluids

We construct a slowly varying space-time dependent holographic superfluid and compute its transport coefficients. Our solution is presented as a series expansion in inverse powers of the charge of the order parameter. We find that the shear viscosity associated with the motion of the condensate vanishes. The diffusion coefficient of the superfluid is continuous across the phase transition while its third bulk viscosity is found to diverge at the critical temperature. As was previously shown, the ratio of the shear viscosity of the normal component to the entropy density is 1/(4 pi). As a consequence of our analysis we obtain an analytic expression for the backreacted metric near the phase transition for a particular type of holographic superfluid.Comment: 45 pages + appendice