2018 Vol. 42, No. 11
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As part of a recent analysis of exclusive two-photon production of W+W- pairs at the LHC, the CMS experiment used di-lepton data to obtain an "effective" photon-photon luminosity. We show how the CMS analysis on their 8 TeV data, along with some assumptions about the likelihood for events in which the proton breaks up to pass the selection criteria, can be used to significantly constrain the photon parton distribution functions, such as those from the CTEQ, MRST, and NNPDF collaborations. We compare the data with predictions using these photon distributions, as well as the new LUXqed photon distribution. We study the impact of including these data on the NNPDF2.3QED, NNPDF3.0QED and CT14QEDinc fits. We find that these data place a useful and complementary cross-check on the photon distribution, which is consistent with the LUXqed prediction while suggesting that the NNPDF photon error band should be significantly reduced. Additionally, we propose a simple model for describing the two-photon production of W+W- at the LHC. Using this model, we constrain the number of inelastic photons that remain after the experimental cuts are applied.
It is known that in supernova explosions, there might be a reverse shock wave in addition to the forward shock wave during the explosion phase, when the mass of supernova is in a certain range. In this paper, we propose to add the reverse shock wave to the previous supernova model, in which only the forward shock wave was included, and thus obtain a new model. By analyzing the resonance condition as well as the density jump in the new model and using the Landau-Zener method, an expression for the crossing probability in high density matter (PH) is given. We proceed to study how PH varies with time and with neutrino energy when both the reverse shock wave and the forward shock wave are considered. From comparison with the previous results, where only the effects of the forward shock wave were considered, it is clear that the reverse shock wave brings significant changes to PH.
The deviation of the measurement of RD (RD*) from the Standard Model (SM) expectation is 2.3σ (3.1σ). RD (RD*) is the ratio of the branching fraction of B → Dτντ (B → D*τντ) to that of B → Dlνl (B → D*lνl), where l=e or μ. This anomaly may imply the existence of new physics (NP). In this paper, we restudy this problem in the supersymmetric extension of the Standard Model with local gauged baryon and lepton numbers (BLMSSM), and give one-loop corrections to RD (RD*).
We study covariant open bosonic string field theories on multiple Dp-branes by using the deformed cubic string field theory, which is equivalent to string field theory in the proper-time gauge. Constructing the Fock space representations of the three-string vertex and the four-string vertex on multiple Dp-branes, we obtain the field theoretical effective action in the zero-slope limit. On multiple D0-branes, the effective action reduces to the Banks-Fishler-Shenker-Susskind (BFSS) matrix model. We also discuss the relation between open string field theory on multiple D-instantons in the zero-slope limit and the Ishibashi-Kawai-Kitazawa-Tsuchiya (IKKT) matrix model. The covariant open string field theory on multiple Dp-branes could be useful to study the non-perturbative properties of quantum field theories in (p+1)-dimensions in the framework of the string theory. The non-zero-slope corrections may be evaluated systematically by using covariant string field theory.
The Bu → ψM decays are studied with the perturbative QCD approach, where the psion ψ=ψ(2S), ψ(3770), ψ(4040) and ψ(4160), and the light meson M=π, K, ρ and K*. The factorizable and non-factorizable contributions, and the S-D wave mixing effects on the psions, are considered in the calculation. With appropriate inputs, the branching ratios for the Bu → ψK decays are generally coincident with the experimental data within errors. However, due to the large theoretical and experimental errors, it is impossible for the moment to give a severe constraint on the S-D wave mixing angles.
A fixed particle number BCS (FBCS) approach is formulated in the relativistic mean field (RMF) model. It is shown that the RMF+FBCS model obtained can describe the weak pairing limit. We calculate the ground-state properties of the calcium isotopes 32-74Ca and compare the results with those obtained from the usual RMF+BCS model. Although the results are quite similar to each other, we observe the interesting phenomenon that for 54Ca, the FBCS approach can enhance the occupation probability of the 2p1/2 single particle level and slightly increases its radius, compared with the RMF+BCS model. This leads to the unusual scenario that although 54Ca is more bound with a spherical configuration, the corresponding size is not the most compact. We anticipate that such a phenomenon might happen for other neutron-rich nuclei and should be checked by further more systematic studies.
Jet measurement is an ideal probe to explore the properties of the hot dense matter created in ultra-relativistic heavy-ion collisions. Recent results at the LHC show that large angle radiation is non-negligible, but the mechanisms and phenomenology of large angle radiation are still unclear and hotly debated. Considering the coexistence and competition of different physics mechanisms qualitatively, it is assumed that the radiation angle is enhanced randomly over a wide range based on the collinear approximation. Its effects on di-jet momentum imbalance, jet fragmentation function and jet shape are studied in pp collisions at 7 TeV. The results show that di-jet asymmetry is insensitive to large angle radiation, while jet shape and jet fragmentation functions are more sensitive and could explain experimental data well. We conclude that de-collimated radiation cannot be ignored for soft jets, and there is a contribution from large angle radiation (φ>0.7) of about 8%, which is significant for jet intrinsic structure measurement at pT,jet<80 GeV/c.
The two-parameter formulae, i.e. the nuclear softness formula and the power index formula, have been used to obtain the band head spin (I0) of the triaxial superdeformed (SD) bands in 163Lu(1, 2, 3, 4), 164Lu(1, 2, 3) and 165Lu(1, 2, 3), in the A~160 mass region. The least squares fitting approach is used. The values of the root mean square (RMS) deviation among the computed and the measured experimental transition energies are obtained by calculating the model parameters. Whenever accurate spins are available, superb agreement is shown between the determined and the measured experimental transition energies. In comparison to the power index formula, the values of band head spin (I0) of the triaxial SD bands in 163Lu(1, 2, 3, 4), 164Lu(1, 2, 3) and 165Lu(1, 2, 3) obtained by the nuclear softness formula are closer to the experimental data. The lowest RMS deviation is also achieved by the nuclear softness formula. Hence, the nuclear softness formula works well for obtaining the band head spin (I0) for the triaxial SD bands in 163Lu(1, 2, 3, 4), 164Lu(1, 2, 3) and 165Lu(1, 2, 3) in the A~160 mass region. The dynamic moment of inertia against hω is also studied.
We explore the end point of the helical instability in a finite density, finite magnetic field background discussed by Kharzeev and Yee. The nonlinear solution is obtained and identified with the (magnetized) chiral density wave phase in the literature. We find there are two branches of solutions, which match the two unstable modes found before. At large chemical potential and magnetic field, the magnetized chiral density wave can be thermodynamically preferred over the chirally symmetric phase and chiral symmetry breaking phase. Interestingly, we find an exotic state with vanishing chemical potential at large magnetic field. We also attempt to clarify the role of anomalous charge in the holographic model.
We extend the complex scaled Green's function (CGF) method to describe resonances with triaxial deformation and present a theoretical formalism. Taking 43S as an example, we elaborate numerical details and demonstrate how to determine the resonance parameters. With changes in the deformation parameters, we study the influence of the triaxial deformation parameter γ on single-particle levels. In particular, the present scheme focuses on the advantages of the complex scaling method (CSM) and the Green's function method, and is suitable for the exploration of resonances.
Starting from the CD-Bonn potential, we have performed Gamow shell-model calculations for neutron-rich oxygen isotopes, investigating excitation spectra and their resonant properties. The Gamow shell model is based on the Berggren ensemble, which is capable of treating the continuum effect reasonably in weakly bound or unbound nuclei. To calculate heavier-mass oxygen isotopes, we choose 16O as a frozen core in the Gamow shell-model calculations. The first 2+ excitation energies of the even-even O isotopes are calculated, and compared with those obtained by the conventional shell model using the empirical USDB interaction. The continuum effect is proved to play an important role in the shell evolution near the drip line. We also discuss the effect of the Berggren contour choice. We improve the approximation in the contour choice to give more precise calculations of resonance widths.
We briefly comment on the paper by Albaladejo et al., Chinese Phys. C 41 121001, rejecting its conclusions.
We investigate many-body correlations caused by two-and three-body (2-, 3bd) forces. Shell-model effective interactions derived from ab initio methods (coupled-cluster method, no-core shell model) are adopted. Vlow-k potentials, based on many-body perturbation theory, are also tested, especially for their cut-off dependence. We compare the central, tensor and spin-orbit interactions from microscopic theory to the fitted interactions. After the inclusion of the three-body force, the matrix elements become fairly close to those fitted directly to experimental data. Calculations of neutron-rich oxygen isotopes are performed, to clarify the effects of 3bd forces, tensor, and spin-orbit interactions on the nuclear binding and excitation energies. We find that the 3bd force can influence the binding energies greatly, which also determines the drip line position, while its effect on excitation energies is not very pronounced. The spin-orbit force, which is part of the 2bd force, can affect the shell structure explicitly, at least for neutron-rich systems.
The surface contamination layer on mirrors can cause significant degradation of the optical performance, which is widely observed in applications, particularly in the fabrication of X-ray focusing telescopes. In this paper, we study the natural contamination layer arising from adsorption precipitation of hydrocarbons or other organic and water molecules in the absence of any external factor. Temporal evolution of the layer formed on super-smooth fused silica, borosilicate glass, and silicon substrates is studied by X-ray reflectometry, atomic force microscopy, and transmission electron microscopy for a one-year period after surface cleaning. The general characteristics of adhesion layer growth are established and discussed. The reconstructed dielectric constant profiles demonstrate that an increase in the adhesion layer thickness, deposited mass and density over time obeys power laws with extremely small exponents. Therefore, the adhesion layer growth is rapid immediately after surface cleaning, with a~1 nm thick layer formed within the first day on all three substrates studied, while the layer density is low (~1 g/cm3). The layer growth on the fused silica and silicon substrates became very slow in the succeeding days, with only a 1.4-1.5 nm thick layer and 1.2-1.3 g/cm3 density after one year of storage in air. At the same time, the adhesion layer growth on the glass substrate showed unexpected acceleration about two months after cleaning, so that the layer thickness reached~2.2 nm after one year of storage. The reason for this effect, which is connected with leaching of the glass, is discussed briefly.
Compelling alternatives to black holes, namely, gravitational vacuum stars (gravastars), which are multilayered compact objects, have been proposed to avoid a number of theoretical problems associated with event horizons and singularities. In this work, we construct a spherically symmetric thin-shell charged gravastar model where the vacuum phase transition between the de Sitter interior and the external Reissner-Nordström spacetime (RN) are matched at a junction surface, by using the cut-and-paste procedure. Gravastar solutions are found among the Guilfoyle exact solutions where the gravitational potential W2 and the electric potential field φ obey a particular relation in a simple form a(b-εφ)2 +b1, where a, b and b1 are arbitrary constants. The simplest ansatz of Guilfoyle's solution is implemented by the following assumption:that the total energy density 8πρm+(Q2/r4) is constant, where Q(r) is the electric charge up to a certain radius r. We show that, for certain ranges of the parameters, we can avoid the horizon formation, which allows us to study the linearized spherically symmetric radial perturbations around static equilibrium solutions. To lend our solution theoretical support, we also analyze the physical and geometrical properties of gravastar configurations.
Planck 2015 data, emphasize that the background geometry during inflation is not pure de Sitter, but from the slow variation of Hubble parameter during the inflationary era, it can be quasi-de Sitter. This motivates us to consider an Asymptotic-de Sitter mode function for reconstructing of initial mode and primordial power spectrum of curvature perturbation. Using Markov Chain Monte Carlo (MCMC) method together with applying recent observational constraints from the Cosmic Microwave Background (CMB) data for the parameterized asymptotic initial mode in term of c, show some deviation from Bunch-Davies mode (c=1). Based on Planck 2015 data release the amplitude of scalar perturbations in 68% confidence level is 109 As=2.94-0.42+0.42 and deviation from Bunch-Davies mode is~0.05, i.e. c~1.05. In this parametrization, the CMB power spectrum of our model shows more red-tilt in comparison with ∧CDM model. Furthermore, we found upper limits for tensor-to-scaler ratio with different pivot scales.
We report a possible dipole anisotropy in acceleration scale g† with 147 rotationally supported galaxies in the local Universe. It is found that a monopole and dipole correction for the radial acceleration relation can better describe the SPARC data set. The monopole term is negligible but the dipole magnitude is significant. It is also found that the dipole correction is mostly induced by anisotropy in the acceleration scale. The magnitude of the ĝ†-dipole reaches 0.25±0.04, and its direction is aligned to (l,b)=(171.30°±7.18°, -15.41°±4.87°), which is very close to the maximum anisotropy direction from the hemisphere comparison method. Furthermore, a robust check shows that the dipole anisotropy could not be reproduced by an isotropic mock data set. However, it is still premature to claim that the Universe is anisotropic, due to the small data samples and uncertainty in the current observations.
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