分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: Multi-field inflation models include a variety of scenarios for how inflation proceeds and ends. Models with the same potential but different kinetic terms are common in the literature. We compare spiral inflation and Dante's inferno-type models, which differ only in their field-space metric. We justify a single-field effective description in these models and relate the single-field description to a mass-matrix formalism. We note the effects of the nontrivial field-space metric on inflationary observables, and consequently on the viability of these models. We also note a duality between spiral inflation and Dante's inferno models with different potentials.
分类: 物理学 >> 核物理学 提交时间: 2016-09-18
摘要: Proton spin is investigated in chiral effective field theory through an examination of the singlet axial charge, a0, and the two non-singlet axial charges, a3 and a8. Finite-range regularization is considered as it provides an effective model for estimating the role of disconnected sea-quark loop contributions to baryon observables. Baryon octet and decuplet intermediate states are included to enrich the spin and flavour structure of the nucleon, redistributing spin under the constraints of chiral symmetry. In this context, the proton spin puzzle is well understood with the calculation describing all three of the axial charges reasonably well. The strange quark contribution to the proton spin is negative with magnitude 0.01. With appropriate Q2 evolution, we find the singlet axial charge at the experimental scale to be a^0=0.31+0.04−0.05, consistent with the range of current experimental values.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: The observed value of the Higgs mass indicates an instability of the Higgs scalar at large energy scales, and hence also at large field values. In the context of early universe cosmology, this is often considered to lead to problems. Here we point out that we can use the instability of the Higgs field to generate an Ekpyrotic phase of contraction. In the context of string theory it is possible that at very high energy densities extra states become massless, leading to an S-brane which leads to the transition between a contracting phase in the past and the current expanding phase. Thus, the Higgs field can be used to generate a non-singular bouncing cosmology in which the anisotropy problem of usual bouncing scenarios is mitigated.
分类: 物理学 >> 核物理学 提交时间: 2016-09-01
摘要: Based on cosmic ray events taken without magnet filed during summer shutdown, we compare the coordinates of hits in muon counter with the expected interaction point of extrapolated tracks from the inner tracking system. By minimizing the difference, we align the muon counter with the inner tracking system. The muon counter is operating in magnetic return yoke and the magnetic field has never been measured before. The strength of the magnetic field of the muon counter is measured for the first time with μ+ and μ− separately. After the alignment and magnetic field measurement, the offsets of hit-position for μ+ and μ− are diminished. The alignment and magnetic field measurement are adopted in the latest BESIII offline software system. This makes physics analysis involving muon counter information more reliable.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2020-11-02
摘要: In this note, we investigate the anomalies in field theories. The results of the anomalies through Feynman diagrams calculation are multi-valued function. These single-valued branches of multi-valued function are related to the bound states of neutral pseudoscalar mesons. Adding these bound state contributions, we obtain a new anomaly free condition that all the external particles are on-shell and find the non-perturbative mass spectrum of neutral pseudoscalar mesons. We also discuss the anomaly in 2 dimensional QFT.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: In this write-up we review and update our recent lattice QCD calculation of B→K∗, Bs→ϕ, and Bs→K∗form factors [arXiv:1310.3722]. These unquenched calculations, performed in the low-recoil kinematic regime, provide a significant improvement over the use of extrapolated light cone sum rule results. The fits presented here include further kinematic constraints and estimates of additional correlations between the different form factor shape parameters. We use these form factors along with Standard Model determinations of Wilson coefficients to give Standard Model predictions for several observables [arXiv:1310.3887]. The modest improvements to the form factor fits lead to improved determinations of FL, the fraction of longitudinally polarized vector mesons, but have little effect on most other observables.
分类: 物理学 >> 核物理学 提交时间: 2023-06-16
摘要: Abstract Main quadrupole magnets are critical for the Circular Electron and Positron Collider (CEPC), and are specifically designed as dual aperture quadrupole (DAQ) magnets. However, the field crosstalk between the two apertures presents challenges. As the CEPC will work at four beam energies of Z, W, Higgs and ttbar mode, the DAQ magnets will operate at four field gradients spanning from 3.18 to 12.63 T/m. The first short quadrupole magnet prototype with the bore diameter of 76 mm and magnetic length of 1.0 m revealed the problems of large magnetic field harmonics and a magnetic center shift within the beam energy range. Accordingly, a compensation method was proposed in this work to solve the field crosstalk effect. By adjusting the gap height at the middle of the two apertures, the field harmonics and magnetic center shift are significantly reduced. After optimization, the short prototype was modified using a new scheme. The field simulations are validated from the magnetic measurement results. Further, the multipole field meets the requirements at the four beam energies. The detailed magnetic field optimization, field harmonics adjustment, and measurement results are presented herein.
分类: 物理学 >> 核物理学 提交时间: 2016-09-18
摘要: Anomalies in recent observational data indicate that there might be some "anisotropic hair" generated in an inflation period. To obtain general information about the effects of this anisotropic hair to inflation models, we studied anisotropic inflation models that involve one vector and one scalar using several types of potentials. We determined the general relationship between the degree of anisotropy and the fraction of the vector and scalar fields, and concluded that the anisotropies behave independently of the potentials. We also generalized our study to the case of multi-directional anisotropies.
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: 2017-05-02
摘要: A novel PM spherical actuator based on three- dimensional pole array is proposed and developed in this paper. Conventionally, 2D pole arrays are widely employed in the design of spherical actuators, which constraints the system torque output greatly. The concept of 3D pole array is aimed at improving the torque performance. The torque has been analyzed and the corresponding analytical model is established based on curve fitting method (CFM) due to the importantance to real-time control. Magnetic force has been studied in a similar way. The results shows that the modeling method has a relatively high precision and can be further used in the real-time control.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: In this paper we investigate the holographic R\'enyi entropy in N=1 supergravity (SUGRA) in AdS3 spacetime, which is dual to the two-dimensional N=(1,1) superconformal field theory (SCFT). We consider both cases of two short intervals on a line with zero temperature and one interval on a circle with low temperature. In SUGRA side we consider contributions of both graviton and gravitino, and in SCFT side we consider contributions of both stress tensor T, ̄T and their superpartners G, ̄G We find matches between SUGRA and SCFT results.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2022-06-21
摘要: In this article, I shall propose an enlightening view on the origin of dark matter abundance, in which I introduce a neutral primordial field, which is a new field beyond the standard model, the mass of the primordial field is confined in the vicinity of neutrino mass (or 1-2 orders of magnitude different from the neutrino mass). All the standard model elementary particles are produced spontaneously from this field in the Big Bang epoch of the universe and then these produced elementary particles decayed or annihilated in the well-known standard model interactions. The relic of the primordial field appears in a form of vacuum energy can not only give naturally the correct abundance of dark matter in the present universe, but provide a natural solution to the cosmological constant problem as well. We find that the conventional methods of detecting dark matter either fail or have great difficulties to detect the remaining vacuum energy of the primordial field, and how to confirm the existence of the remaining energy of the universe's original energy in experiment is still an open problem.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-08
摘要: We explicitly show that split-universal extra dimension (split-UED), a recently suggested extension of universal extra dimension (UED) model, can nicely explain recent anomalies in cosmic-ray positrons and electrons observed by PAMELA and ATIC/PPB-BETS. Kaluza-Klein (KK)dark matters mainly annihilate into leptons because the hadronic branching fraction is highly suppressed by large KK quark masses and the antiproton flux agrees very well with the observation where no excess is found. The flux of cosmic gamma-rays from pion decay is also highly suppressed and hardly detected in low energy region (E-gamma less than or similar to 20GeV). Collider signatures of colored KK particles at the LHC, especially q(1)q(1) production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard p(T) jets and missing E-T are generated, which make it possible to suppress the standard model background and discover the signals.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2020-09-17
摘要: In this work, we try to find a way to describe the physical law of micro-world under the frame of a space-time theory. By introducing a scalar field D(x), we rewrite the action of conventional field theory and the Lagrangian describing the motion of the particle, where a modified space-time relation is obtained. To prove the correctness of this attempt, we derive the Klein-Gordon equation by the Hamilton-Jacobi method in four dimensional form.
分类: 物理学 >> 核物理学 提交时间: 2017-08-22
摘要: Pseudospin symmetry is a relativistic symmetry of the Dirac Hamiltonian with scalar and vector mean fields equal and opposite in sign. This symmetry imposes constraints on the Dirac eigen- functions. We examine extensively the Dirac eigenfunctions of realistic relativistic mean field calcu- lations of deformed nuclei to determine if these eigenfunctions satisfy these pseudospin symmetry constraints.
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: Apparent softening of the symmetry energy with the inclusion of hyperon and quark degrees of freedom is demonstrated by the fact that the phase transition causes the change of the interaction and the suppression of nucleon fractions. The demonstration is fulfilled in the relativistic mean-field model.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: Newly born magnetars are promising sources for gravitational wave (GW) detection due to their ultra-strong magnetic fields and high spin frequencies. Within the scenario of a growing tilt angle between the star's spin and magnetic axis, due to the effect of internal viscosity, we obtain improved estimates of the stochastic gravitational wave backgrounds (SGWBs) from magnetic deformation of newly born magnetars. We find that the GW background spectra contributed by the magnetars with ultra-strong toroidal magnetic fields of 10^{17} G could roughly be divided into four segments. Most notably, in contrast to the background spectra calculated by assuming constant tilt angles \chi=\pi/2, the background radiation above 1000 Hz are seriously suppressed. However, the background radiation at the frequency band \sim100-1000 Hz are moderately enhanced, depending on the strengths of the dipole magnetic fields. We suggest that if all newly born magnetars indeed have toroidal magnetic fields of 10^{17} G, the produced SGWBs should show sharp variations with the observed frequency at several tens to about 100 hertz. If these features could be observed through sophisticated detection of the SGWB using the proposed Einstein Telescope, it will provide us a direct evidence of the tilt angle evolutions and further some deep understandings about the properties of newly born magnetars.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-04
摘要: For magnetic reconnection to proceed, the frozen-in condition for both ion fluid and electron fluid in a localized diffusion region must be violated by inertial effects, thermal pressure effects, or inter-species collisions. It has been unclear which underlying effects unfreeze ion fluid in the diffusion region. By analyzing in situ THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft measurements at the dayside magnetopause, we present clear evidence that the off-diagonal components of the ion pressure tensor is mainly responsible for breaking the ion frozen-in condition in reconnection. The off-diagonal pressure tensor, which corresponds to a non-gyrotropic pressure effect in this event, is a fluid manifestation of ion demagnetization in the diffusion region. From the perspective of the ion momentum equation, the reported non-gyrotropic ion pressure tensor is a fundamental aspect in specifying the reconnection electric field that controls how quickly reconnection proceeds.
分类: 地球科学 >> 地球科学史 提交时间: 2020-06-22 合作期刊: 《干旱区科学》
摘要: Snow resisting capacity of vegetation is important for secondary distribution of water resources in seasonal snow areas of grassland because it affects the regeneration, growth and nutrient circulation of vegetation in grassland. This study investigated vegetation characteristics (canopy height, canopy length and crown width) of Caragana microphylla Lam. (shrub) and Achnatherum splendens (Trin.) Nevski. (herb), and snow morphologies (snow depth, snow width and snow braid length) in a typical steppe region of Inner Mongolia, China in 2017. And the influence of vegetation characteristic on snow resisting capacity (the indices of bottom area of snow and snow volume reflect snow resisting capacity) was analyzed. The results showed that snow morphology depends on vegetation characteristics of shrub and herb. The canopy height was found to have the greatest influence on snow depth and the crown width had the greatest influence on snow width. The canopy length was found to have little influence on morphological parameters of snow. When the windward areas of C. microphylla and A. splendens were within the ranges of 0.0–0.5 m2 and 0.0–8.0 m2, respectively, the variation of snow cover was large; however, beyond these areas, the variation of snow cover became gradually stable. The potential area of snow retardation for a single plant was 1.5–2.5 m2 and the amount of snow resistance was 0.15–0.20 m3. The bottom area of snow and snow volume (i.e., snow resisting capacity) of clumped C. microphylla and A. splendens was found to be 4 and 25 times that of individual plant, respectively. The results could provide a theoretical basis both for the estimation of snow cover and the establishment of a plant-based technical system for the control of windblown snow in the typical steppe region of Inner Mongolia.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: In the last years it has been shown that some properties of strongly coupled superconductors can be potentially described by classical general relativity living in one higher dimension, which is known as holographic superconductors. This paper gives a quick and introductory overview of some holographic superconductor models with s-wave, p-wave and d-wave orders in the literature from point of view of bottom-up, and summarizes some basic properties of these holographic models in various regimes. The competition and coexistence of these superconductivity orders are also studied in these superconductor models.
分类: 物理学 >> 核物理学 提交时间: 2024-03-10
摘要: Currently, three types of superconducting magnets are used in particle accelerators: cos2uptheta, CCT, and serpentine. However, all three coil configurations have complex spatial geometries, which make magnet manufacturing and strain-sensitive superconductor applications difficult. Compared with the three existing quadrupole coils, the racetrack quadrupole coil has a simple shape and manufacturing process, but there have been few theoretical studies. In this paper, the two-dimensional and three-dimensional analytical expressions for the magnetic field in coil-dominated racetrack superconducting quadrupole magnets are presented. The analytical expressions of the field harmonics and gradient are fully resolved and depend only on the geometric parameters of the coil and current density. Then, a genetic algorithm is applied to obtain a solution for the coil geometry parameters with field harmonics on the order of 10-4. Finally, considering the practical engineering needs of the accelerator interaction region, electromagnetic design examples of racetrack quadrupole magnets with high gradients, large apertures, and small apertures are described, and the application prospects of racetrack quadrupole coils are analyzed.