X-boson cumulant approach to the periodic Anderson model

The Periodic Anderson Model (PAM) can be studied in the infinite U limit by employing the Hubbard X operators to project out the unwanted states. We have already studied this problem employing the cumulant expansion with the hybridization as perturbation, but the probability conservation of the local states (completeness) is not usually satisfied when partial expansions like the Chain Approximation (CHA) are employed. Here we treat the problem by a technique inspired in the mean field approximation of Coleman's slave-bosons method, and we obtain a description that avoids the unwanted phase transition that appears in the mean-field slave-boson method both when the chemical potential is greater than the localized level Ef at low temperatures (T) and for all parameters at intermediate T.Comment: Submited to Physical Review B 14 pages, 17 eps figures inserted in the tex

Constraining the variation of the coupling constants with big bang nucleosynthesis

We consider the possibility of the coupling constants of the $SU(3)\times SU(2)\times U(1)$ gauge interactions at the time of big bang nucleosynthesis having taken different values from what we measure at present, and investigate the allowed difference requiring the shift in the coupling constants not violate the successful calculation of the primordial abundances of the light elements. We vary gauge couplings and Yukawa couplings (fermion masses) using a model in which their relative variations are governed by a single scalar field, dilaton, as found in string theory. The results include a limit on the fine structure constant $-6.0\times10^{-4}<\Delta\alpha_{EM}/\alpha_{EM}<1.5\times10^{-4}$, which is two orders stricter than the limit obtained by considering the variation of $\alpha_{EM}$ alone.Comment: 7 page

The effect of twisted magnetic field on the resonant absorption of MHD waves in coronal loops

The standing quasi modes in a cylindrical incompressible flux tube with magnetic twist that undergoes a radial density structuring is considered in ideal magnetohydrodynamics (MHD). The radial structuring is assumed to be a linearly varying density profile. Using the relevant connection formulae, the dispersion relation for the MHD waves is derived and solved numerically to obtain both the frequencies and damping rates of the fundamental and first-overtone modes of both the kink (m=1) and fluting (m=2,3) waves. It was found that a magnetic twist will increase the frequencies, damping rates and the ratio of the oscillation frequency to the damping rate of these modes. The period ratio P_1/P_2 of the fundamental and its first-overtone surface waves for kink (m=1) and fluting (m=2,3) modes is lower than 2 (the value for an untwisted loop) in the presence of twisted magnetic field. For the kink modes, particularly, the magnetic twists B_{\phi}/B_z=0.0065 and 0.0255 can achieve deviations from 2 of the same order of magnitude as in the observations. Furthermore, for the fundamental kink body waves, the frequency bandwidth increases with increasing the magnetic twist.Comment: 18 pages, 9 figure

Tubular structures of GaS

In this Brief Report we demonstrate, using density-functional tight-binding theory, that gallium sulfide (GaS) tubular nanostructures are stable and energetically viable. The GaS-based nanotubes have a semiconducting direct gap which grows towards the value of two-dimensional hexagonal GaS sheet and is in contrast to carbon nanotubes largely independent of chirality. We further report on the mechanical properties of the GaS-based nanotubes

Combined CI+MBPT calculations of energy levels and transition amplitudes in Be, Mg, Ca, and Sr

Configuration interaction (CI) calculations in atoms with two valence electrons, carried out in the V(N-2) Hartree-Fock potential of the core, are corrected for core-valence interactions using many-body perturbation theory (MBPT). Two variants of the mixed CI+MBPT theory are described and applied to obtain energy levels and transition amplitudes for Be, Mg, Ca, and Sr

Theta angle versus CP violation in the leptonic sector

Assuming that the axion mechanism of solving the strong CP problem does not exist and the vanishing of theta at tree level is achieved by some model-building means, we study the naturalness of having large CP-violating sources in the leptonic sector. We consider the radiative mechanisms which transfer a possibly large CP-violating phase in the leptonic sector to the theta parameter. It is found that large theta cannot be induced in the models with one Higgs doublet as at least three loops are required in this case. In the models with two or more Higgs doublets the dominant source of theta is the phases in the scalar potential, induced by CP violation in leptonic sector. Thus, in the MSSM framework the imaginary part of the trilinear soft-breaking parameter A_l generates the corrections to the theta angle already at one loop. These corrections are large, excluding the possibility of large phases, unless the universality in the slepton sector is strongly violated.Comment: 5 pages, 2 figure

Scale of fermion mass generation

Unitarity of longitudinal weak vector boson scattering implies an upper bound on the scale of electroweak symmetry breaking, $\Lambda_{EWSB}\equiv \sqrt{8\pi}v\approx$ 1 TeV. Appelquist and Chanowitz have derived an analogous upper bound on the scale of fermion mass generation, proportional to $v^2/m_f$, by considering the scattering of same-helicity fermions into pairs of longitudinal weak vector bosons in a theory without a standard Higgs boson. We show that there is no upper bound, beyond that on the scale of electroweak symmetry breaking, in such a theory. This result is obtained by considering the same process, but with a large number of longitudinal weak vector bosons in the final state. We further argue that there is no scale of (Dirac) fermion mass generation in the standard model. In contrast, there is an upper bound on the scale of Majorana-neutrino mass generation, given by $\Lambda_{Maj}\equiv 4\pi v^2/m_\nu$. In general, the upper bound on the scale of fermion mass generation depends on the dimensionality of the interaction responsible for generating the fermion mass. We explore the scale of fermion mass generation in a variety of excursions from the standard model: models with fermions in nonstandard representations, a theory with higher-dimension interactions, a two-Higgs-doublet model, and models without a Higgs boson.Comment: 31 pages, 9 figures; version accepted for publication in Phys. Rev.

Phase I/II trial of concurrent extracranial palliative radiation therapy with Dabrafenib and Trametinib in metastatic BRAF V600E/K mutation-positive cutaneous Melanoma

Background: Concurrent treatment with BRAF inhibitors and palliative radiation therapy (RT) could be associated with increased toxicity, especially skin toxicity. Current Eastern Cooperative Oncology Group (ECOG) consensus guideline recommend ceasing BRAF inhibitors during RT. There is a lack of data regarding concurrent RT with combined BRAF and MEK inhibitors. This single-arm phase I/II trial was designed to assess the safety and tolerability of palliative RT with concurrent Dabrafenib and Trametinib in patients with BRAF-mutant metastatic melanoma. Materials and methods: Patients received Dabrafenib and Trametinib before and during palliative RT to soft tissue, nodal or bony metastases. The RT dose was escalated stepwise during the study period. Toxicity data including clinical photographs of the irradiated area was collected for up to 12 months following completion of RT. Results: Between June 2016 to October 2019, ten patients were enrolled before the study was stopped early due to low accrual rate. Six patients were treated at level 1 (20 Gy in 5 fractions, any location) and 4 patients at level 2a (30 Gy in 10 fractions with no abdominal viscera exposed). All alive patients completed one year of post-RT follow-up. Of the 82 adverse events (AEs) documented, the majority (90%) were grade 1 and 2. Eight grade 3 events (10%) occurred in five patients, only one was treatment-related (grade 3 fever due to Dabrafenib and Trametinib). No patients experienced grade 3 or 4 RT related toxicities, including skin toxicities. One serious AE was documented in relation to a grade 3 fever due to Dabrafenib and Trametinib requiring hospitalisation. Conclusions: The lack of grade 3 and 4 RT-related toxicities in our study suggests that Dabrafenib and Trametinib may be continued concurrently during fractionated non-visceral palliative RT to extracranial sites

The sensitivity of the vortex filament method to different reconnection models

We present a detailed analysis on the effect of using different algorithms to model the reconnection of vortices in quantum turbulence, using the thin-filament approach. We examine differences between four main algorithms for the case of turbulence driven by a counterflow. In calculating the velocity field we use both the local induction approximation (LIA) and the full Biot-Savart integral. We show that results of Biot-Savart simulations are not sensitive to the particular reconnection method used, but LIA results are.Comment: 9 pages, 9 figure

Solar Wakes of Dark Matter Flows

We analyze the effect of the Sun's gravitational field on a flow of cold dark matter (CDM) through the solar system in the limit where the velocity dispersion of the flow vanishes. The exact density and velocity distributions are derived in the case where the Sun is a point mass. The results are extended to the more realistic case where the Sun has a finite size spherically symmetric mass distribution. We find that regions of infinite density, called caustics, appear. One such region is a line caustic on the axis of symmetry, downstream from the Sun, where the flow trajectories cross. Another is a cone-shaped caustic surface near the trajectories of maximum scattering angle. The trajectories forming the conical caustic pass through the Sun's interior and probe the solar mass distribution, raising the possibility that the solar mass distribution may some day be measured by a dark matter detector on Earth. We generalize our results to the case of flows with continuous velocity distributions, such as that predicted by the isothermal model of the Milky Way halo.Comment: 30 pages, 8 figure