2018 Vol. 42, No. 1
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The Chiral Magnetic Effect (CME) is a macroscopic manifestation of fundamental chiral anomaly in a many-body system of chiral fermions, and emerges as an anomalous transport current in the fluid dynamics framework. Experimental observation of the CME is of great interest and has been reported in Dirac and Weyl semimetals. Significant efforts have also been made to look for the CME in heavy ion collisions. Critically needed for such a search is the theoretical prediction for the CME signal. In this paper we report a first quantitative modeling framework, Anomalous Viscous Fluid Dynamics (AVFD), which computes the evolution of fermion currents on top of realistic bulk evolution in heavy ion collisions and simultaneously accounts for both anomalous and normal viscous transport effects. AVFD allows a quantitative understanding of the generation and evolution of CME-induced charge separation during the hydrodynamic stage, as well as its dependence on theoretical ingredients. With reasonable estimates of key parameters, the AVFD simulations provide the first phenomenologically successful explanation of the measured signal in 200 AGeV AuAu collisions.
The light unflavoured meson η/η' decays are valuable for testing non-perturbative quantum chromodynamics and exploring new physics beyond the Standard Model. This paper describes a series of event generators, including η/η'→γl+l-, η/η'→γπ+π-, η'→ωe+e-, η→π+π-π0, η/η'→π0π0π0, η'→ηππ and η'→π+π-π+π-/π+π-π0π0, which have been developed for investigating η/η decay dynamics. For most of these generators, their usability has been validated in BESⅢ analyses for determining the detection efficiency, and background studies. The consistency between data and Monte Carlo shows that these generators work well in the BESⅢ simulation, and will also be useful for ongoing BESⅢ analyses and other experiments for studying η/η physics.
While indirect and direct CP violation (CPV) has been established in the decays of strange and beauty mesons, no CPV has yet been found for baryons. There are different paths to finding CP asymmetry in the decays of strange baryons; they are all highly non-trivial. The HyperCP Collaboration has probed CPV in the decays of single Ξ and Λ. We discuss future lessons from e+e- collisions at BESⅢ/BEPCⅡ:probing decays of pairs of strange baryons, namely Λ, ∑ and Ξ. Realistic goals are to learn about non-perturbative QCD. One can hope to find CPV in the decays of strange baryons; one can also dream of finding the impact of New Dynamics. We point out that an important new era will start with the BESⅢ/BEPCⅡ data accumulated by the end of 2018. This also supports new ideas to trigger J/ψ → Λ Λ at the LHCb collaboration.
Maxwell electrodynamics in the fixed Minkowski space-time background can be described in an equivalent way in a curved Riemannian geometry that depends on the electromagnetic field and that we call the electromagnetic metric (e-metric for short). After showing such geometric equivalence we investigate the possibility that new processes dependent on the e-metric are allowed. In particular, for very high values of the field, a direct coupling of uncharged particles to the electromagnetic field may appear.
Motivated by the simple toroidal compactification of extra-dimensional SUSY theories, we investigate a partial N=2 supersymmetric (SUSY) extension of the standard model which has an N=2 SUSY sector and an N=1 SUSY sector. We point out that below the scale of the partial breaking of N=2 to N=1, the ratio of Yukawa to gauge couplings embedded in the original N=2 gauge interaction in the N=2 sector becomes greater due to a fixed point. Since at the partial breaking scale the sfermion masses in the N=2 sector are suppressed due to the N=2 non-renormalization theorem, the anomaly mediation effect becomes important. If dominant, the anomaly-induced masses for the sfermions in the N=2 sector are almost UV-insensitive due to the fixed point. Interestingly, these masses are always positive, i.e. there is no tachyonic slepton problem. From an example model, we show interesting phenomena differing from ordinary MSSM. In particular, the dark matter particle can be a sbino, i.e. the scalar component of the N=2 vector multiplet of U(1)Y. To obtain the correct dark matter abundance, the mass of the sbino, as well as the MSSM sparticles in the N=2 sector which have a typical mass pattern of anomaly mediation, is required to be small. Therefore, this scenario can be tested and confirmed in the LHC and may be further confirmed by the measurement of the N=2 Yukawa couplings in future colliders. This model can explain dark matter, the muon g-2 anomaly, and gauge coupling unification, and relaxes some ordinary problems within the MSSM. It is also compatible with thermal leptogenesis.
We discuss the implications of the recently reported RK and RK* anomalies, the lepton flavor non-universality in the B→ Kl+l- and B→ K*l+l- decay channels. Using two sets of hadronic inputs of form factors, we perform a fit of new physics to the RK and RK* data, and significant new physics contributions are found. We suggest the study of lepton flavor universality in a number of related rare B, Bs,Bc and Λb decay channels, and in particular we give predictions for the μ-to-e ratios of decay widths with different polarizations of the final state particles, and of the b→ dl+l- processes, which are presumably more sensitive to the structure of the underlying new physics. With the new physics contributions embedded in the Wilson coefficients, we present theoretical predictions for lepton flavor non-universality in these processes.
We construct a holographic superconductor model, based on a gravity theory, which exhibits novel metal-insulator transitions. We investigate the condition for the condensation of the scalar field over the parameter space, and then focus on the superconductivity over the insulating phase with a hard gap, which is supposed to be Mott-like. It turns out that the formation of the hard gap in the insulating phase benefits the superconductivity. This phenomenon is analogous to the fact that the pseudogap phase can promote the pre-pairing of electrons in high Tc cuprates. We expect that this work can shed light on understanding the mechanism of high Tc superconductivity from the holographic side.
A massive self-duality solution associated with invariant 1-forms is presented. At the zero mass limit the massive self-dual theory of the SO(3) gauge group on 4 dimensions cannot be reduced to that of massless self-duality. In such a case the self-dual connection turns to the flat connection and one cannot obtain a massless theory in such an approach.
We investigate the baryon number susceptibilities up to fourth order along different freeze-out lines in a holographic QCD model with a critical end point (CEP), and we propose that the peaked baryon number susceptibilities along the freeze-out line can be used as a clean signature to locate the CEP in the QCD phase diagram. On the temperature and baryon chemical potential plane, the cumulant ratio of the baryon number susceptibilities (up to fourth order) forms a ridge along the phase boundary, and develops a sword-shaped "mountain" standing upright around the CEP in a narrow and oblate region. The measurement of baryon number susceptibilities from heavy-ion collision experiments is along the freeze-out line. If the freeze-out line crosses the foot of the CEP mountain, then one can observe the peaked baryon number susceptibilities along the freeze-out line, and the kurtosis of the baryon number distributions has the highest magnitude. The data from the first phase of the beam energy scan program at the Relativistic Heavy Ion Collider indicates that there should be a peak of the kurtosis of the baryon number distribution at a collision energy of around 5 GeV, which suggests that the freeze-out line crosses the foot of the CEP mountain and the summit of the CEP should be located nearby, around a collision energy of 3-7 GeV.
Recent measurements of charge-dependent azimuthal correlations in high-energy heavy-ion collisions have indicated charge-separation signals perpendicular to the reaction plane, and have been related to the chiral magnetic effect (CME). However, the correlation signal is contaminated with the background caused by the collective motion (flow) of the collision system, and an effective approach is needed to remove the flow background from the correlation. We present a method study with simplified Monte Carlo simulations and a multi-phase transport model, and develop a scheme to reveal the true CME signal via event-shape engineering with the flow vector of the particles of interest.
The pygmy dipole resonance (PDR) of nickel isotopes is studied using the deformed random phase approximation method. The isoscalar character of the pygmy resonance is confirmed, and the correlation between the pygmy resonance and neutron skin thickness is discussed. Our investigation shows a linear correlation between PDR integral cross section and neutron skin thickness when the excess neutrons lie in pf orbits, with a correlation rate of about 0.27 fm-1. However, in more neutron-rich nickel isotopes, the growth of the pygmy dipole resonance is stagnant. Although the neutron skin thickness increases, the whole skin is not active. There is an inertial part in the nuclei 70-78Ni which does not participate in the pygmy resonance actively and as a result, contributes little to the photo-absorption cross section.
We study the multiplicity fluctuation and correlation of identified mesons and baryons formed at hadronization by the quark combination mechanism in the context of ultra-relativistic heavy-ion collisions. Based on the statistical method of free quark combination, we derive the two-hadron multiplicity correlations, including meson-meson and meson-baryon correlations, and take the effects of quark number fluctuation at hadronization into account by a Taylor expansion method. After including the decay contributions, we calculate the dynamical fluctuation observable vdyn for Kπ, pπ and Kp pairs and discuss what underlying physics can be obtained by comparing with data from Pb-Pb collisions at √ =2.76 TeV and simulations from the HIJING and AMPT event generators.
Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the need for a relativistic chiral force in relativistic nuclear structure studies, we explore a new relativistic scheme to construct the nucleon-nucleon interaction in the framework of covariant chiral effective field theory. The chiral interaction is formulated up to leading order with covariant power counting and a Lorentz invariant chiral Lagrangian. We find that the relativistic scheme induces all six spin operators needed to describe the nuclear force. A detailed investigation of the partial wave potentials shows a better description of the 1S0 and 3P0 phase shifts than the leading order Weinberg approach, and similar to that of the next-to-leading order Weinberg approach. For the other partial waves with angular momenta J ≥ 1, the relativistic results are almost the same as their leading order non-relativistic counterparts.
We present a formula for proton radioactivity half-lives of spherical proton emitters with the inclusion of the spectroscopic factor. The coefficients in the formula are calibrated with the available experimental data. As an input to calculate the half-life, the spectroscopic factor that characterizes the important information on nuclear structure should be obtained with a nuclear many-body approach. This formula is found to work quite well, and in better agreement with experimental measurements than other theoretical models. Therefore, it can be used as a powerful tool in the investigation of proton emission, in particular for experimentalists.
We apply a recently proposed covariant power counting in nucleon-nucleon interactions to study strangeness S=-1 ΛN-∑N interactions in chiral effective field theory. At leading order, Lorentz invariance introduces 12 low energy constants, in contrast to the heavy baryon approach, where only five appear. The Kadyshevsky equation is adopted to resum the potential in order to account for the non-perturbative nature of hyperon-nucleon interactions. A fit to the 36 hyperon-nucleon scattering data points yields χ2≈ 16, which is comparable with the sophisticated phenomenological models and the next-to-leading order heavy baryon approach. However, one cannot achieve a simultaneous description of the nucleon-nucleon phase shifts and strangeness S=-1 hyperon-nucleon scattering data at leading order.
We investigate the effect of proton-skin thickness on the α decay process. We consider 188 neutron-deficient nuclei belonging to the isotopic chains from Te (Z=52) to Pb (Z=82). The calculations of the half-life are carried out in the framework of the preformed cluster model, with the Wentzel-Kramers-Brillouin penetration probability and assault frequency. It is shown that the proton-skin thickness (△p) of the daughter nucleus gives rise to a total α-daughter nucleus interaction potential of relatively wide deep internal pocket and a thinner Coulomb barrier of less height. This increases the penetration probability but decreases the assault frequency. The overall impact of the proton-skin thickness appears as a decrease in the decay half-life. The proton-skin thickness decreases the stability of the nucleus. The half-lives of the proton-skinned isotopes along the isotopic chain decrease exponentially with increasing the proton-skin thickness, whereas the Qα-value increases with △p. α -decay manifests itself as the second favorite decay mode of neutron-deficient nuclei, next to the β+-decay and before proton-decay. It is indicated as main, competing, and minor decay mode, at 21%, 7%, and 57%, respectively, of the investigated nuclei.
The thermonuclear 19F(p,α0)16O reaction rate in the temperature region 0.007-10 GK has been derived by re-evaluating the available experimental data, together with the low-energy theoretical R-matrix extrapolations. Our new rate deviates by up to about 30% compared to the previous results, although all rates are consistent within the uncertainties. At very low temperature (e.g. 0.01 GK) our reaction rate is about 20% lower than the most recently published rate, because of a difference in the low energy extrapolated S-factor and a more accurate estimate of the reduced mass used in the calculation of the reaction rate. At temperatures above~1 GK, our rate is lower, for instance, by about 20% around 1.75 GK, because we have re-evaluated the previous data (Isoya et al., Nucl. Phys. 7, 116 (1958)) in a meticulous way. The present interpretation is supported by the direct experimental data. The uncertainties of the present evaluated rate are estimated to be about 20% in the temperature region below 0.2 GK, and are mainly caused by the lack of low-energy experimental data and the large uncertainties in the existing data. Asymptotic giant branch (AGB) stars evolve at temperatures below 0.2 GK, where the 19F(p,α)16O reaction may play a very important role. However, the current accuracy of the reaction rate is insufficient to help to describe, in a careful way, the fluorine over-abundances observed in AGB stars. Precise cross section (or S factor) data in the low energy region are therefore needed for astrophysical nucleosynthesis studies.
The original mimetic model was proposed to take the role of dark matter. In this paper we consider possible direct interactions of mimetic dark matter with other matter in the universe, especially standard model particles such as baryons and photons. By imposing shift symmetry, the mimetic dark matter field can only have derivative couplings. We discuss the possibilities of generating baryon number asymmetry and cosmic birefringence in the universe based on the derivative couplings of mimetic dark matter to baryons and photons.
The search is now on for new materials that can be used for ionic stripping. Materials that maximize the stripping of the structural ion are important for conducting experiments with quark-gluon plasma. Although this paper is a theoretical study, it offers practical applications, in heavy-ion accelerators, of the new effect of collision multiplicity with high-energy ions interacting with polyatomic targets. It is shown that internal nanostructured targets in which the collision multiplicity effect is manifested can more efficiently strip out structural ions compared to standard internal targets for stripping. A target consisting of oriented nano-tubes with the C240 chirality (10,0) is considered as an example. A comparison with the stripping process on a carbon target with the same number of misaligned atoms in a unit of volume C is provided.
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