Optical deep space communication via relay satellite

The possible use of an optical for high rate data transmission from a deep space vehicle to an Earth-orbiting relay satellite while RF links are envisioned for the relay to Earth link was studied. A preliminary link analysis is presented for initial sizing of optical components and power levels, in terms of achievable data rates and feasible range distances. Modulation formats are restricted to pulsed laser operation, involving bot coded and uncoded schemes. The advantage of an optical link over present RF deep space link capabilities is shown. The problems of acquisition, pointing and tracking with narrow optical beams are presented and discussed. Mathematical models of beam trackers are derived, aiding in the design of such systems for minimizing beam pointing errors. The expected orbital geometry between spacecraft and relay satellite, and its impact on beam pointing dynamics are discussed

A combinatorial smoothness criterion for spherical varieties

We suggest a combinatorial criterion for the smoothness of an arbitrary spherical variety using the classification of multiplicity-free spaces, generalizing an earlier result of Camus for spherical varieties of type $A$.Comment: 14 pages, 2 table

Carbon-Oxygen White Dwarfs Accreting CO-Rich Matter I: A Comparison Between Rotating and Non-Rotating Models

We investigate the lifting effect of rotation on the thermal evolution of CO WDs accreting CO-rich matter. We find that rotation induces the cooling of the accreting star so that the delivered gravitational energy causes a greater expansion with respect to the standard non-rotating case. The increase in the surface radius produces a decrease in the surface value of the critical angular velocity and, therefore, the accreting WD becomes gravitationally unbound (Roche instability). This occurrence is due to an increase in the total angular momentum of the accreting WD and depends critically on the amount of specific angular momentum deposited by the accreted matter. If the specific angular momentum of the accreted matter is equal to that of the outer layers of the accreting structure, the Roche instability occurs well before the accreting WD can attain the physical conditions for C-burning. If the values of both initial angular velocity and accretion rate are small, we find that the accreting WD undergoes a secular instability when its total mass approaches 1.4 Msun. At this stage, the ratio between the rotational and the gravitational binding energy of the WD becomes of the order of 0.1, so that the star must deform by adopting an elliptical shape. In this case, since the angular velocity of the WD is as large as 1 rad/s, the anisotropic mass distribution induces the loss of rotational energy and angular momentum via GWR. We find that, independent of the braking efficiency, the WD contracts and achieves the physical conditions suitable for explosive C-burning at the center so that a type Ia supernova event is produced.Comment: 39 pages, 22 eps-figures; accepted for publication in Astrophysical Journa

Rotated twisted-mass: a convenient regularization scheme for isospin breaking QCD and QED lattice calculations

We propose a scheme of lattice twisted-mass fermion regularization which is particularly convenient for application to isospin breaking (IB) QCD and QED calculations, based in particular on the so called RM123 approach, in which the IB terms of the action are treated as a perturbation. The main, practical advantage of this scheme is that it allows the calculation of IB effects on some mesonic observables, like e.g. the pi+ - pi0 mass splitting, using lattice correlation functions in which the quark and antiquark fields in the meson are regularized with opposite values of the Wilson parameter r. These correlation functions are found to be affected by much smaller statistical fluctuations, with respect to the analogous functions in which quark and antiquark fields are regularized with the same value of r. Two numerical application of this scheme, that we call "rotated twisted-mass", within pure QCD and QCD+QED respectively, are also provided for illustration.Comment: 17 pages, 2 figure

Astrophysical S factor for the radiative capture 12N(p,gamma)13O determined from the 14N(12N,13O)13C proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus 12N was investigated using the Asymptotic Normalization Coefficient (ANC) method. We have used the 14N(12N,13O)13C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13O -> 12N + p and calculate from it the direct component of the astrophysical S factor of the 12N(p,gamma)13O reaction. The optical potentials used and the DWBA analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time with the transfer measurement. From the transfer, we determined the square of the ANC, C^2(13Og.s.) = 2.53 +/- 0.30 fm-1, and hence a value of 0.33(4) keVb was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of Stotal(0) = 0.42(5) keVb. The 12N(p,gamma)13O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.Comment: 15 pages, 10 figures, 3 tables submitted to Phys. Rev.

Spectral-function determination of complex electroweak amplitudes with lattice QCD

We present a novel method to determine on the lattice both the real and imaginary parts of complex electroweak amplitudes involving two external currents and a single hadron or the QCD vacuum in the external states. The method is based on the spectral representation of the relevant time-dependent correlation functions and, by extending the range of applicability of other recent proposals built on the same techniques, overcomes the difficulties related to the analytic continuation from Minkowskian to Euclidean time, arising when intermediate states with energies smaller than the external states contribute to the amplitude. In its simplest form, the method relies on the standard iϵ prescription to regularize the Feynman integrals and at finite ϵ it requires to verify the condition 1/L≪ϵ≪Δ(E), where L is the spatial extent of the lattice and, for any given energy E, Δ(E) represents the typical size of the interval around E in which the hadronic amplitude is significantly varying. In order to illustrate the effectiveness of this approach in a realistic case, we apply the method to evaluate nonperturbatively the hadronic amplitude contributing to the radiative leptonic decay Ds→ℓνℓγ*, working for simplicity with a single lattice ensemble at fixed volume and lattice spacing

First direct lattice calculation of the chiral perturbation theory low-energy constant ℓ7

We evaluate by means of lattice QCD calculations the low-energy constant ℓ7 which parametrizes strong isospin effects at next-to-leading order (NLO) in SU(2) chiral perturbation theory. Among all low-energy constants at NLO, ℓ7 is the one known less precisely, and its uncertainty is currently larger than 50%. Our strategy is based on the RM123 approach in which the lattice path-integral is expanded in powers of the isospin breaking parameter Δm=(md−mu)/2. In order to evaluate the relevant lattice correlators we make use of the recently proposed rotated twisted-mass (RTM) scheme. Within the RM123 approach, it is possible to cleanly extract the value of ℓ7 from either the pion mass splitting Mπ+−Mπ0 induced by strong isospin breaking at order O((Δm)2) (mass method), or from the coupling of the neutral pion π0 to the isoscalar operator (¯uγ5u+¯dγ5d)/√2 at order O(Δm) (matrix element method). In this pilot study we limit the analysis to a single ensemble generated by the Extended Twisted Mass Collaboration (ETMC) with Nf=2+1+1 dynamical quark flavors, which corresponds to a lattice spacing a≃0.095  fm and to a pion mass Mπ≃260  MeV. We find that the matrix element method outperforms the mass method in terms of resulting statistical accuracy. Our determination, ℓ7=2.5(1.4)×10−3, is in agreement and improves previous calculations

Ubiquitination of HIV-1 and MuLV Gag

AbstractOur previous biochemical studies of HIV-1 and MuLV virions isolated and identified mature Gag products, HIV-1 p6Gag and MuLV p12Gag, that were conjugated to a single ubiquitin. To study the importance of the monoubiquitination of Gag, a series of lysine to arginine mutants were constructed that eliminated ubiquitination at one or both of the lysines in HIV-1NL4-3 p6Gag and both lysines in Moloney MuLV p12Gag. HPLC and immunoblot analysis of the HIV-1 mutants demonstrated that either of the lysines in p6Gag, K27 or K33, could be monoubiquitinated. However, infectivity assays showed that monoubiquitination of HIV-1 p6Gag or MuLV p12Gag is not required for viral replication in vitro. Pulse-chase radiolabeling of HIV-1-producing cells revealed that monoubiquitination of p6Gag does not affect the short-term release of virus from the cell, the maturation of Pr55Gag, or the sensitivity of these processes to proteasome inhibitors. Experiments with protease-deficient HIV-1 showed that Pr55Gag can be monoubiquitinated, suggesting that p6Gag is first modified as a domain within Gag. Examination of the proteins inside an HIV-1 mutant found that free ubiquitin was incorporated into the virions in the absence of the lysines in p6Gag, showing that the ubiquitin inside the virus is not initially brought in as a p6Gag conjugate. Although our results establish that monoubiquitination of p6Gag and p12Gag is not required for viral replication in vitro, this modification may be a by-product of interactions between Gag and cellular proteins during assembly and budding

Inclusive hadronic decay rate of the τ lepton from lattice QCD

Inclusive hadronic decays of the τ lepton are very interesting from the phenomenological point of view since they give access to the Cabibbo-Kobayashi-Maskawa matrix elements Vud and Vus. In this paper, for the first time, by employing the method of [M. Hansen, A. Lupo, and N. Tantalo, Phys. Rev. D 99, 094508 (2019)] for hadronic smeared spectral densities, we compute on the lattice the inclusive decay rate of the processes τ→Xudντ, where Xud is a generic hadronic state with u¯d flavor quantum numbers. Our computation, which avoids any recourse to operator product expansion and/or perturbative approximations, is carried out in isospin symmetric Nf=2+1+1 lattice QCD at physical quark masses, using ensembles produced by the Extended Twisted Mass Collaboration at three lattice spacings and two volumes. All uncertainties, except for isospin breaking effects, are taken into account and a result with a subpercent error is obtained for |Vud|, which is nicely consistent with the current world average. These findings validate our approach and also motivate the inclusion of isospin breaking corrections and its extension to the inclusive decay τ→Xusντ, paving the way toward a high-precision first-principles determination of |Vus| and |Vud| from inclusive τ decay