Physics Letters B最新文献

We present coupled-cluster computations of nuclei with neutron number $N=50$ “south” of ⁷⁸Ni using nucleon-nucleon and three-nucleon forces from chiral effective field theory. We find an erosion of the magic number $N=50$ toward ⁷⁰Ca manifesting itself by an onset of deformation and increased complexity in the ground states. For ⁷⁸Ni, we predict a low-lying rotational band consistent with recent data, which up until now has been a challenge for ab initio nuclear models. Ground states are deformed in ⁷⁶Fe, ⁷⁴Cr, and ⁷²Ti, although the spherical states are too close in energy to unambiguously identify the shape of the ground state within the uncertainty estimates. In ⁷⁰Ca, the potential energy landscape from quadrupole-constrained Hartree-Fock computations flattens, and the deformation becomes less rigid. We also compute the low-lying spectra and $B\left(E2\right)$ values for these neutron-rich $N=50$ nuclei.

In Ref. [10], we proposed to replace the final dark matter (DM) particle in the semi-annihilation mode $\mathrm{DM}+\mathrm{DM}\to \mathrm{antiDM}+\mathrm{Higgs boson}$ with its $Z_{N\ge 3}$ companion, thus reducing DM number density without DM-nucleon scattering. In this work, we study the indirect detection signals from DM annihilation, the Higgs boson pair with one of them from the companion decay being on- or off- shell, depending on the DM-companion mass splitting. We generate the photon spectrum by using PYTHIA8 and study the properties of the spectrum, to find that the hard part of the spectrum in our model is mainly shaped by the direct Higgs boson and thus does not differ much from that of the conventional semi-annihilation mode. Using the Fermi-LAT data of dwarf spheroidal galaxies, we derive the current limit of the DM annihilation cross section for $\mathrm{DM}+\mathrm{DM}\to \mathrm{companio}{n}^{⁎}+\mathrm{Higgs boson}$, and for the relatively light DM, it reaches the typical thermal cross section. However, for the TeV scale DM, we have to rely on the Cherenkov Telescope Array, which is able to rule out the whole parameter space except for the coannihilation region.

A machine-learning algorithm, Light Gradient Boosting Machine, was applied for the first time to investigate the fundamental experimental observables in even-even nuclei over the Segrè chart. Specifically, we focused on the excitation energies of the $2_1^{+}$ and $4_1^{+}$ states, and the reduced electric quadrupole transition probability $B(E2;0_1^{+}\to 2_1^{+})$. Present obtained results well reproduced experimental data within an accuracy of 1.07, 1.05, and 1.14 times for the $2_1^{+}$ and $4_1^{+}$ states as well as $B(E2;0_1^{+}\to 2_1^{+})$, respectively, being significantly precise than the results from any state-of-the-art nuclear models and from any machine-learning-based approaches. The predictive capability of our machine learning methodology was further validated using 17 newly measured data points which were not used in the training set. Taking O, Ca, Sn, and Pb isotopes as examples, it has been found that our methodology precisely captures both the isotopic trend and absolute values, surpassing all theoretical models hitherto. Our findings reveal the double-magic nature of ¹⁰⁰Sn and the disappearance of the $N=20$ shell in ²⁸O.

We present a Rabi-type measurement of two ground-state hydrogen hyperfine transitions performed in two opposite external magnetic field directions. This puts first constraints at the level of

The high momentum tail (HMT) in the momentum distribution of nucleons above the Fermi surface has been regarded as an evidence of short-range correlations (SRCs) in atomic nuclei. It has been showcased recently that the np Bremsstrahlung radiation in heavy ion reactions can be used to extract HMT information. The Richardson-Lucy (RL) algorithm is introduced to the reconstruction of the original Bremsstrahlung γ-ray energy spectrum from experimental measurements. By solving the inverse problem of the detector response to the γ-rays, the original energy spectrum of the Bremsstrahlung γ in 25 MeV/u ⁸⁶Kr + ¹²⁴Sn has been reconstructed and compared to the isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) simulations. The analysis based on hypothesis test suggests the existence of the HMT of nucleons in nuclei, in accordance with the previous conclusions. With its effectiveness being demonstrated, it is feasible to apply the RL algorithm in future experiments of measuring the Bremsstrahlung γ-rays in heavy ion reactions.

In this paper, the m-component super KP hierarchy in form of free superfermions is constructed by Clifford superalgebra. The super bosonic counterpart of this hierarchy is described by using the vertex operators. Based on this, some super Hirota equations are determined and the bilinear identity is expressed by super Baker functions and tau function. Darboux transformation in terms of superfermions is also discussed.

Character expansions are among the most important approaches to modern quantum field theory, which substitute integrals by combinations of peculiar special functions from the Schur-Macdonald family. These formulas allow various deformations, which are not transparent in integral formulation. We analyze from this point of view the Itzykson-Zuber integral over unitary matrices which is exactly solvable, but difficult to deform in β and $(q,t)$ directions. Character expansion straightforwardly resolves this problem. However, taking averages with the so defined measure can look problematic, because integrals of individual expansion terms often diverge and well defined is only the sum of them. We explain a way to overcome this problem by Gaussian regularization, which can have a broad range of further applications.

In the Standard Model of particle physics, the axial current is not conserved, due both to fermion masses and to the axial anomaly. Using perturbative quantum chromodynamics, we calculate matrix elements of the local and non-local axial current for a gluon target, clarifying their connection with the axial anomaly. In so doing, we also reconsider classic results obtained in the context of the nucleon spin sum rule as well as recent results for off-forward kinematics. An important role is played by the infrared regulator, for which we put a special emphasis on the nonzero quark mass. We highlight cancellations that take place between contributions from the axial anomaly and the quark mass, and we elaborate on the relation of those cancellations with the conservation of angular momentum.

The Λ hyperon spin flip and non-flip cross sections are calculated in a simple hadronic model by including both the s-channel process involving the spin 3/2, positive parity ${\Sigma }^{⁎}\left(1358\right)$ resonance and the t-channel process via the exchange of a scalar σ meson. Because of its large mass, the Λ spin flip to non-flip cross sections is negligibly small in the t-channel process compared to the constant value of 1/3.5 in the s-channel process. With the s-channel $\Lambda -\pi$ spin-dependent cross sections included in a schematic kinetic model, the effects of hadronic scatterings on the Λ spin polarization in Au-Au collisions at $\sqrt{s_{NN}}=7.7$ GeV are studied. It is found that the Λ spin polarization only decreases by 7-12% during the hadronic stage of these collisions, which justifies the assumption in theoretical studies that compare the Λ polarization calculated at the chemical freezeout to the measured one at the kinetic freezeout.

We present new, exact, rotating and accelerating solutions within the framework of five-dimensional Einstein-Gauss-Bonnet theory at the Chern-Simons point. The rotating solutions describe black holes characterized by a single rotation parameter, a mass parameter, and two extra integration constants that can be interpreted as hairs of a gravitational nature. It is noteworthy that the rotation cannot be removed by a large diffeomorphism. We also extend our procedure to dimension seven, providing a new rotating solution with two rotation parameters pertaining to cubic Lovelock theory with a unique vacuum.