Pion properties at finite isospin chemical potential with isospin symmetry breaking

Pion properties at finite temperature, finite isospin and baryon chemical potentials are investigated within the SU（2） NJL model. In the mean field approximation for quarks and random phase approximation fpr mesons, we calculate the pion mass, the decay constant and the phase diagram with different quark masses for the u quark and d quark, related to QCD corrections, for the first time. Our results show an asymmetry between μI 〈 0 and μI 〉0 in the phase diagram, and different values for the charged pion mass（or decay constant） and neutral pion mass（or decay constant） at finite temperature and finite isospin chemical potential. This is caused by the effect of isospin symmetry breaking, which is from different quark masses.

Spectroscopic factors of resonance states with the Gamow shell model

We provide an investigation of the spectroscopic factor of resonance states in A=5-8 nuclei,utilizing the Gamow shell model(GSM).Within the GSM,the configuration mixing is taken into account exactly with the shell model framework,and the continuum coupling is addressed via the complex-energy Berggren ensemble,which treats bound,resonance,and non-resonant continuum single-particle states on an equal footing.As a result,both the configuration mixing and continuum coupling are meticulously considered in the GSM.We first calculate the low-lying states of helium isotopes and isotones with the GSM,and the results are compared with that of ab initio no-core shell model(NCSM)calculations.The results indicate that GSM can reproduce the low-lying resonance states more accurately than the NCSM.Following this,we delve into the spectroscopic factors of the resonance states as computed through both GSM and NCSM,concurrently conducting systematic calculations of overlap functions pertinent to these resonance states.Finally,the calculated overlap function and spectroscopic factor of6He(01+)■νp3/2→^(7)He(3/2_(1)-)with GSM are compared with the results from ab initio NCSM,variational Monte Carlo,and Green’s function Monte Carlo calculations,as well as available experimental data.The results assert that wave function asymptotes can only be reproduced in GSM,where resonance and continuum coupling are precisely addressed.

Ab initio calculations of mirror energy difference in sd-shell nuclei

Mirror energy difference is a key observable in isospin symmetry breaking,containing rich information about nuclear structure.Understanding the mechanisms underlying mirror energy difference is important in nuclear physics.In the present work,we extensively investigated mirror energy difference using ab initio valence-space inmedium similarity renormalization group approach,focusing specifically on sd-shell nuclei.The low-lying spectra of Al isotopes and N=8 isotones,together with their mirror nuclei,were calculated,followed by a systematic analysis of the evolution of the mirror energy difference.The results suggest that the large mirror energy difference is mainly caused by the weakly-bound effects and large average occupations of the 1s1/2 orbit.Lastly,we compare the results of our ab initio calculations with shell model results,elucidating the relationship and coherence between these two models.

Can VMD improve the estimate of the muon g-2?

We show that a VMD based theoretical input allows for a significantly improved accuracy for the hadronic vacuum polarization of the photon which contributes to the theoretical estimate of the muon g-2. We also show that the only experimental piece of information in the τ decay which cannot be accounted for within this VMD framework is the accepted value for Br（τ→ππvτ）, while the T spectum lineshape is in agreement with expectations from e^＋e^- annihilations.

Testing CVC and CKM Unitarity via Superallowed Nuclear Beta Decay

Superallowed nuclear beta decay between 0^+analog states is a sensitive probe of the weak interaction, with the established strength – or F t value – of each such transition being a direct measure of the vector coupling constant, GV. Each transition's F t value depends on the half-life of the parent nucleus as well as on the Q-value and branching ratio for the transition of interest. It also depends on small(~1%) transition-dependent theoretical corrections, of which the most sensitive accounts for isospin symmetry breaking. We have recently published a new survey of world superallowed-decay data, which establishes the F t values of 14 separate superallowed transitions to a precision of order 0.1% or better.The results from this very robust data set yield the value of Vud, the up-down quark mixing element of the Cabibbo-Kobayashi-Maskawa(CKM) matrix, and lead to the most demanding test available of CKM unitarity. The survey results and their outcome are described, as is the current direction of experiments that focus on testing the validity of the isospin-symmetry-breaking corrections.