分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-09-27
摘要： The measured masses of the Higgs boson and top quark indicate that the e#11;ective potential of the standard model either develops an unstable electroweak vacuum or stands stable all the way up to the Planck scale. In the latter case in which the top quark mass is about 2#27; below its present central value, the Higgs boson can be the inaton with the help of a large nonminimal coupling to curvature in four dimensions. We propose a scenario in which the Higgs boson can be the in aton in a#12;ve-dimensional Gauss-Bonnet braneworld model to solve both the unitarity and stability problems which usually plague Higgs ination. We #12;nd that in order for Higgs ination to happen successfully in the Gauss-Bonnet regime, the extra dimension scale must appear roughly in the range between the TeV scale and the instability scale of standard model. At the tree level, our model can give rise to a naturally small nonminimal coupling #24; #24; O(1) for the Higgs quartic coupling #21; #24; O(0:1) if the extra dimension scale lies at the TeV scale. At the loop level, the in ationary predictions at the treelevel are preserved. Our model can be confronted with future experiments and observations fromboth particle physics and cosmology.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-09-27
摘要： We investigate the in uence on the in ationary predictions from the reheating processes char-acterized by the e-folding number Nreh and the e ective equation-of-state parameter wreh during the reheating phase. For the rst time, reheating processes can be constrained in the Nreh wreh plane from Planck 2015. We nd that for Higgs in ation with a nonminimal coupling to gravity, the predictions are insensitive to the reheating phase for current CMB measurements. We also nd that the spontaneously broken SUSY in ation and axion monodromy in ation with 2=3 potential, which with instantaneous reheating lie outside or at the edge of the 95% con dence region in the ns r plane from Planck 2015 TT,TE,EE+lowP, can well t the data with the help of reheating processes. Future CMB experiments would put strong constraints on reheating processes.
分类： 物理学 >> 核物理学 提交时间： 2017-08-22
摘要： The pseudospin symmetry is a relativistic dynamical symmetry connected with the small com- ponent of the Dirac spinor. The origin of pseudospin symmetry in single particle bound states in atomic nuclei has been revealed and studied extensively. By examining the zeros of Jost functions corresponding to the small components of Dirac wave functions and phase shifts of continuum states, we show that the pseudospin symmetry in single particle resonant states in nuclei is conserved when the attractive scalar and repulsive vector potentials have the same magnitude but opposite sign. The exact conservation and the breaking of pseudospin symmetry are illustrated for single particle resonances in spherical square-well and Woods-Saxon potentials.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： We have developed multi-dimensional constrained covariant density functional theories (MDC-CDFT) for finite nuclei in which the shape degrees of freedom βλμ with even μ, e.g., β20, β22, β30, β32, β40, etc., can be described simultaneously. The functional can be one of the following four forms: the meson exchange or point-coupling nucleon interactions combined with the non-linear or density-dependent couplings. For the pp channel, either the BCS approach or the Bogoliubov transformation is implemented. The MDC-CDFTs with the BCS approach for the pairing (in the following labelled as MDC-RMF models with RMF standing for “relativistic mean field”) have been applied to investigate multi-dimensional potential energy surfaces and the non-axial octupole Y32-correlations in N = 150 isotones. In this contribution we present briefly the formalism of MDC-RMF models and some results from these models. The potential energy surfaces with and without triaxial deformations are compared and it is found that the triaxiality plays an important role upon the second fission barriers of actinide nuclei. In the study of Y32-correlations in N = 150 isotones, it is found that, for 248Cf and 250Fm, β32 > 0.03 and the energy is lowered by the β32 distortion by more than 300 keV; while for 246Cm and 252No, the pocket with respect to β32 is quite shallow.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： Background: The pseudospin symmetry (PSS) has been studied extensively for bound states. Recently we justified rigorously that the PSS in single particle resonant states is exactly conserved when the attractive scalar and repulsive vector potentials of the Dirac Hamiltonian have the same magnitude but opposite sign [Phys. Rev. Lett. 109, 072501 (2012)]. Purpose: To understand more deeply the PSS in single particle resonant states, we focus on several issues related to the exact conservation and breaking mechanism of the PSS in single particle resonances. In particular, we are interested in how the energy and width splittings of PS partners depend on the depth of the scalar and vector potentials. Methods: We investigate the asymptotic behaviors of radial Dirac wave functions. Spherical square well poten- tials are employed in which the PSS breaking part in the Jost function can be well isolated. By examining the zeros of Jost functions corresponding to small components of the radial Dirac wave functions, general properties of the PSS are analyzed. Results: By examining the Jost function, the occurrence of intruder orbitals is explained and it is possible to trace continuously the PSS partners from the PSS limit to the case with a finite potential depth. The dependence of the PSS in resonances as well as in bound states on the potential depth is investigated systematically. We find a threshold effect in the energy splitting and an anomaly in the width splitting of pseudospin partners when the depth of the single particle potential varies from zero to a finite value. Conclusions: The conservation and the breaking of the PSS in resonant states and bound states share some similar properties. The appearance of intruder states can be explained by examining the zeros of Jost functions. Origins of the threshold effect in the energy splitting and the anomaly in the width splitting of PS partners, together with many other problems, are still open and should be further investigated.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： The pseudospin symmetry (PSS) is a relativistic dynamical symmetry directly connected with the small component of the nucleon Dirac wave function. Much effort has been made to study this symmetry in bound states. Recently, a rigorous justification of the PSS in single particle resonant states was achieved by examining the asymptotic behaviors of the radial Dirac wave functions: The PSS in single particle resonant states in nuclei is conserved exactly when the attractive scalar and repulsive vector potentials have the same magnitude but opposite sign. Several issues related to the exact conservation and breaking mechanism of the PSS in single particle resonances were investigated by employing spherical square well potentials in which the PSS breaking part can be well isolated in the Jost function. A threshold effect in the energy splitting and an anomaly in the width splitting of pseudospin partners were found when the depth of the square well potential varies from zero to a finite value.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： In this contribution we present some results of potential energy sur- faces of actinide and transfermium nuclei from multi-dimensional constrained relativistic mean field (MDC-RMF) models. Recently we developed multi-dimensional constrained covariant density func- tional theories (MDC-CDFT) in which all shape degrees of freedom βλμ with even μ are allowed and the functional can be one of the following four forms: the meson exchange or point-coupling nucleon interactions combined with the non-linear or density-dependent cou- plings. In MDC-RMF models, the pairing correlations are treated with the BCS method. With MDC-RMF models, the potential energy surfaces of even-even actinide nuclei were investigated and the effect of triaxiality on the fission barriers in these nuclei was discussed. The non-axial reflection-asymmetric β32 shape in some βλμ =0 β22 ̸=0 β20 >0 β30 ̸=0 β20 0 β20 ≫0 transfermium nuclei with N = 150, namely and 252No were also studied.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： Background: Many different shape degrees of freedom play crucial roles in determining the nuclear ground state and saddle point properties and the fission path. For the study of nuclear potential energy surfaces, it is desirable to have microscopic and self-consistent models in which all known important shape degrees of freedom are included. Purpose: By breaking both the axial and the spatial reflection symmetries simultaneously, we develop multidimensionally-constrained relativistic mean field (MDC-RMF) models. Methods: The nuclear shape is assumed to be invariant under the reversion of x and y axes, i.e., the intrinsic symmetry group is V4 and all shape degrees of freedom βλμ with even μ, such as β20, β22, β30, β32, β40, ..., are included self-consistently. The single-particle wave functions are expanded in an axially deformed harmonic oscillator (ADHO) basis. The RMF functional can be one of the following four forms: the meson exchange or point-coupling nucleon interactions combined with the nonlinear or density-dependent couplings. The pairing effects are taken into account with the BCS approach. Results: The one-, two, and three-dimensional potential energy surfaces of 240Pu are illustrated for numerical checks and for the study of the effect of the triaxiality on the fission barriers. Potential energy curves of even-even actinide nuclei around the first and second fission barriers are studied systematically. Besides the first ones, the second fission barriers in these nuclei are also lowered considerably by the triaxial deformation. This lowering effect is independent of the effective interactions used in the RMF functionals. Further discussions are made about different predictions on the effect of the triaxiality between the macroscopic-microscopic and MDC-RMF models, possible discontinuities on PES’s from self-consistent approaches, and the restoration of broken symmetries. Conclusions: MDC-RMF models give a reasonably good description of fission barriers of even-even actinide nuclei. It is important to include both the nonaxial and the reflection asymmetric shapes simultaneously for the study of potential energy surfaces and fission barriers of actinide nuclei and of those in unknown mass regions such as, e.g., superheavy nuclei.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-03
摘要： The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to b ¯b via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small κ/λ and a negative Aκ can also lead to a successful strongly first order electroweak phase transition
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to bb¯ via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small κ/λ and a negative Aκ can also lead to a successful strongly first order electroweak phase transition.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： In quantum gravity, a foamy structure of space-time leads to Lorentz invariance violation (LIV). As the most energetic astrophysical processes in the Universe, gamma-ray bursts (GRBs) provide an effective way to probe quantum gravity effects. We use continuous spectra of 20 short GRBs detected by the Swift satellite to give a conservative lower limit of quantum gravity energy scale MQG. Due to the LIV effect, photons with different energy have different velocities. This will lead to the delayed arrival of high energy photons relative to the low energy ones. Based on the fact that the LIV-induced time delay can't be longer than the duration of a GRB, we present the most conservative estimation of the quantum gravity energy scales from 20 short GRBs. The most strict constraint,MQG>5.05* 1014 GeV, is from GRB 140622A.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We probe the possible anisotropy of the Universe by using the JLA compilation of type-Ia supernovae. We apply the Markov Chain Monte Carlo (MCMC) method to constrain the amplitude and direction of anisotropy in three cosmological models. For the dipole-modulated ΛCDM model, the anisotropic amplitude is consistent with zero at 68% C.L., and has an upper bound AD<1.98×10−3 at 95% C.L. Regardless of much larger uncertainty, we find the dipole direction of JLA is amazingly opposite to that of Union2. Similar results are found for the dipole-modulated wCDM and CPL models. Thus, the Universe is still well consistent with the isotropy according to the JLA compilation.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： By assuming that the scalar meson K∗0(1430) belongs to the first excited states or the lowest lying ground states, we study the pure annihilation-type decays B→K∗±0(1430)K(∗)∓ in the QCD factorization approach. Within the standard model, the branching fractions are at the order of 10−8−10−7, which is possible to be measured in the ongoing LHCb experiment or forthcoming Belle-II experiment. We also study these decays in the family non-universal Z′ model. The results show that if mZ′≈600GeV (ζ=0.02), both the branching fractions and CPasymmetries of B¯¯¯¯0→K∗+0(1430)K− could be changed remarkably, which provides us a place for probing the effect of new physics. These results could be used to constrain the parameters of Z′ model.
分类： 物理学 >> 核物理学 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： The nuclear dynamical deformation, the fusion probability and the evaporation residue (ER) cross sections for the synthesis of superheavy nuclei are studied with the di-nuclear system model and the related dynamical potential energy surface. The intrinsic energy and the maximum dynamical deformations for 48Ca+248Cm are calculated. The effect of dynamical deformation on the potential energy surface and fusion is investigated. It is found that the dynamical deformation influences the potential energy surface and fusion probability significantly. The dependence of the fusion probability on the angular momentum is investigated. The ER cross sections for some superheavy nuclei in 48Ca induced reactions are calculated and it is found that the theoretical results are in good agreement with the experimental results.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We calculate the tree and penguin amplitudes in the B0→π+π− decay channel employing the perturbative QCD factorization approach. Using the amplitudes as input with the theoretical uncertainties sufficiently considered, we constrain the UT angle γ to 53∘≤γ≤70∘, from the measurements of the CP violation parameters Cπ+π− and Sπ+π− in B0→π+π−. The U-spin breaking effect between B0→π+π− and B0s→K+K− is estimated to be around 30\%.
分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2016-05-03
摘要： An efficient novel algorithm was developed to estimate the Density of States (DOS) for large systems by calculating the ensemble means of an extensive physical variable, such as the potential energy, U, in generalized canonical ensembles to interpolate the interior reverse temperature curve beta S(U) partial derivative S(U)/partial derivative U, where S(U) is the logarithm of the DOS. This curve is computed with different accuracies in different energy regions to capture the dependence of the reverse temperature on U without setting prior grid in the U space. By combining with a U-compression transformation, we decrease the computational complexity from O(N-3/2) in the normal Wang Landau type method to O(N-1/2) in the current algorithm, as the degrees of freedom of system N. The efficiency of the algorithm is demonstrated by applying to Lennard Jones fluids with various N, along with its ability to find different macroscopic states, including metastable states.
分类： 物理学 >> 核物理学 提交时间： 2017-08-22
摘要： The non-axial reflection-asymmetric β32 shape in some transfermium nuclei with N = 150, namely 246Cm, 248Cf, 250Fm, and 252No are investigated with multidimensional constrained covariant den- sity functional theories. By using the density-dependent point coupling covariant density functional theory with the parameter set DD-PC1 in the particle-hole channel, it is found that, for the ground states of 248Cf and 250Fm, the non-axial octupole deformation parameter β32 > 0.03 and the energy gain due to the β32 distortion is larger than 300 keV. In 246Cm and 252No, shallow β32 minima are found. The occurrence of the non-axial octupole β32 correlations is mainly from a pair of neutron orbitals [734]9/2 (νj15/2) and [622]5/2 (νg9/2) which are close to the neutron Fermi surface and a pair of proton orbitals [521]3/2 (πf7/2) and [633]7/2 (πi13/2) which are close to the proton Fermi surface. The dependence of the non-axial octupole effects on the form of energy density functional and on the parameter set is also studied.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： Multi-dimensional constrained covariant density functional theories were developed recently. In these theories, all shape degrees of freedom βλμ deformations with even μ are allowed, e.g., β20, β22, β30, β32, β40, β42, β44, and so on and the CDFT functional can be one of the following four forms: the meson exchange or point-coupling nucleon interactions combined with the non-linear or density-dependent couplings. In this contri- bution, some applications of these theories are presented. The potential energy surfaces of actinide nuclei in the (β20 , β22 , β30 ) deformation space are investigated. It is found that besides the octupole deformation, the triaxiality also plays an important role upon the second fission barriers. The non-axial reflection-asymmetric β32 shape in some transfermium nuclei with N = 150, namely 246Cm, 248Cf, 250Fm, and 252No are studied.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： We investigate the one-body dissipation dynamics in heavy-ion collisions of 16O+16O using a fully three-dimensional time-dependent Hartree-Fock (TDHF) theory with the modern Skyrme energy functional and without any symmetry restrictions. The energy dissipation is revealed to decrease in deep-inelastic collisions of the light systems as the bombarding energy increases owing to the competition between collective motion and single-particle degrees of freedom. The role of spin-orbit force is given particular emphasis in deep-inelastic collisions. The spin-orbit force causes a significant enhancement of the dissipation. The time-even coupling of spin-orbit force plays a dominant role at low energies, while the influence of time-odd terms is notable at high energies. About 40-65% of the total dissipation depending on the different parameter sets is predicted to arise from the spin-orbit force. The theoretical fusion cross section has a reasonably good agreement with the experimental data, considering that no free parameters are adjusted to reaction dynamics in the TDHF approach.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-25
摘要： The light-like cusp anomalous dimension is a universal function in the analysis of infrared divergences. In maximally (N = 4) supersymmetric Yang– Mills theory (SYM) in the planar limit, it is known, in principle, to all loop orders. The non-planar corrections are not known in any theory, with the first appearing at the four-loop order. The simplest quantity which contains this correction is the four-loop two-point form factor of the stress tensor multiplet. This form factor was largely obtained in integrand form in a previous work for N = 4 SYM, up to a free parameter. In this work, a reduction of the appearing integrals obtained by solving integration-by-parts (IBP) identities using a modified version of Reduze is reported. The form factor is shown to be independent of the remaining parameter at integrand level due to an intricate pattern of cancellations after IBP reduction. Moreover, two of the integral topologies vanish after reduction. The appearing master integrals are cross-checked using independent algebraic-geometry techniques explored in the Mint package. The latter results provide the basis of master integrals applicable to generic form factors, including those in Quantum Chromodynamics. Discrepancies between explicitly solving the IBP relations and the MINT approach are highlighted. Remaining bottlenecks to completing the computation of the four-loop non-planar cusp anomalous dimension in N = 4 SYM and beyond are identified.
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