In the calculation of the collisional energy loss of hard partons in the hot quark gluon plasma, loop corrections to the tree-level amplitudes are essential: Not only do they provide the necessary screening of long-range interactions, but they also induce the momentum dependence of the coupling α. The latter fact, as we argued recently, leads to a crucial modification of the hitherto existing theory of this observable. Instead of ${\mathit{dE}}_{\mathrm{coll}}^B/\mathit{dx}~{\alpha }^2{T}^2\ln (\mathit{ET}/m_D^2)$, as first derived by Bjorken, the mean energy loss actually reads ${\mathit{dE}}_{\mathrm{coll}}/\mathit{dx}~\alpha (m_D^2)T^2$ for $E\gg T$. Here we evaluate, within this mended framework, a less “inclusive” quantity, namely the probability distribution (“quenching weights”) of the collisional energy loss, which is necessary to describe jet quenching in heavy-ion collisions. The result is unambiguously determined by ${\Lambda }_{\mathrm{QCD}}$ (whereas previous approaches involved “guessing” a value for the coupling). Representative Monte Carlo simulations then suggest a substantial collisional component of jet quenching—which hints at a natural explanation of the “single electron puzzle.”

The two-neutrino double-β decay matrix elements and half-lives of ${}^{48}\mathrm{Ca}$ were calculated within a shell-model approach for transitions to the ground state and to the $2^{+}$ first excited state of ${}^{48}\mathrm{Ti}$. We use the full $\mathit{pf}$ model space and the GXPF1A interaction, which was recently proposed to describe the spectroscopic properties of the nuclei in the nuclear mass region $A=47$–66. Our results are $T_{1/2}(0^{+}\to 0^{+})=3.3\times {10}^{19}$ yr and $T_{1/2}(0^{+}\to 2^{+})=8.5\times {10}^{23}$ yr. The result for the decay to the ${}^{48}\mathrm{Ti}$ $0^{+}$ ground state is in good agreement with experiment. The half-life for the decay to the $2^{+}$ state is two orders of magnitude larger than that obtained previously.

The exclusive production of one ${\mu }^{+}{\mu }^{-}$ pair in collisions of two ultrarelativistic nuclei is considered. We present a simple method for the calculation of the Born cross section for this process based on an improved equivalent photon approximation. We find that the Coulomb corrections to this cross section (corresponding to multiphoton exchange of the produced ${\mu }^{\pm }$ with the nuclei) are small, whereas the unitarity corrections (corresponding to the exchange of light-by-light blocks between nuclei) are large. This is in sharp contrast to the exclusive $e^{+}{e}^{-}$ pair production where the Coulomb corrections to the Born cross section are large, whereas the unitarity corrections are small. We calculate also the cross section for the production of one ${\mu }^{+}{\mu }^{-}$ pair and several $e^{+}{e}^{-}$ pairs in the leading logarithmic approximation. Using this cross section we find that the inclusive production of ${\mu }^{+}{\mu }^{-}$ pair coincides in this approximation with its Born value.

We calculate the hypertriton binding energy and the $\Lambda d$ and $\Sigma d$ scattering lengths using baryon-baryon interactions obtained from a chiral constituent quark model. We study consistently the $\Lambda \mathit{NN}$ and $\Sigma \mathit{NN}$ systems by analyzing the effect of the $\Sigma \leftrightarrow \Lambda$ conversion. Our interactions correctly predict the hypertriton binding energy. The $(I,J)=(0,3/2)$ $\Lambda \mathit{NN}$ channel is also attractive and it might have a bound state. From the condition of nonexistence of a (0,3/2) $\Lambda \mathit{NN}$ bound state, an upper limit for the spin-triplet $\Lambda N$ scattering length is obtained. We also present results for the elastic and inelastic $\Sigma N$ and $\Lambda N$ cross sections. The consistent description of the $\Sigma N$ scattering cross sections imposes a lower limit for the corresponding spin-triplet scattering lengths. In the $\Sigma \mathit{NN}$ system the only attractive channels are $(I,J)=(1,1/2)$ and $(0,1/2)$, the $(1,1/2)$ state being the most attractive one.

We show that a consequence of isospin symmetry, recently discovered in mirror conjugated one-nucleon decays, can be extended to mirror-conjugated α-particle decays, both virtual and real. For virtual α decays of bound mirror pairs this symmetry manifests itself as a relation between the asymptotic normalization coefficients (ANCs) of α-particle overlap integrals. This relation is given by a simple analytical formula that involves α-particle separation energies and charges of residual nuclei. For bound-unbound mirror pairs, the ANC of a bound nucleus is related to the α width of the mirror unbound level. For unbound mirror pairs we get a new analytical formula that relates the widths of mirror resonances. We test the validity of these analytical formulas against the predictions of a two-body potential and of a many-body microscopic cluster model for several mirror states in ${}^7\mathrm{Li}$-${}^7\mathrm{Be}$, ${}^{11}\mathrm{B}$-${}^{11}\mathrm{C}$, and ${}^{19}\mathrm{F}$-${}^{19}\mathrm{Ne}$ isotopes. We show that these analytical formulas are valid in many cases but that some deviations can be expected for isotopes with strongly deformed and easily excited cores. In general, the results from microscopic model are not very sensitive to model assumptions and can be used to predict unknown astrophysically relevant cross sections using known information about mirror systems.

Central collisions of gold nuclei are simulated by several existing models and the central net baryon density ρ and the energy density ɛ are extracted at successive times for beam kinetic energies of 5–40 GeV/nucleon. The resulting trajectories in the $(\rho ,\varepsilon )$ phase plane are discussed from the perspective of experimentally exploring the expected first-order hadronization phase transition with the planned FAIR at GSI or in a low-energy campaign at the Relativistic Heavy Ion Collider.

The flux of ${}^7\mathrm{Be}$ and ${}^8\mathrm{B}$ neutrinos from the Sun and the production of ${}^7\mathrm{Li}$ via primordial nucleosynthesis depend on the rate of the ${}^3\mathrm{He}$($\alpha ,\gamma$)${}^7\mathrm{Be}$ reaction. In an extension of a previous study showing cross section data at 127–167 keV center-of-mass energy, the present work reports on a measurement of the ${}^3\mathrm{He}$($\alpha ,\gamma$)${}^7\mathrm{Be}$ cross section at 106 keV performed at Italy's Gran Sasso underground laboratory by the activation method. This energy is closer to the solar Gamow energy than ever reached before. The result is $\sigma =0.567\pm 0.{029}_{\mathrm{stat}}\pm 0.{016}_{\mathrm{syst}}$ nb. The data are compared with previous activation studies at high energy, and a recommended $S(0)$ value for all ${}^3\mathrm{He}$($\alpha ,\gamma$)${}^7\mathrm{Be}$ activation studies, including the present work, is given.

Many calculations for the production of light and intermediate particles resulting from heavy ion collisions at intermediate energies exist. Calculations of properties of the largest fragment resulting from multifragmentation are rare. In this paper we compute these properties and compare them with the data for the case of gold on carbon. We use the canonical thermodynamic model. The model also gives a bimodal distribution for the largest fragment in a narrow energy range.

Superscaling properties of ${}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}$, and ${}^{40}\mathrm{Ca}$ nuclear responses, induced by electron and neutrino scattering, are studied for momentum transfer values between 300 and 700 MeV/$c$. We have defined two indexes to have quantitative estimates of the scaling quality. We have analyzed experimental responses to get the empirical values of the two indexes. We have then investigated the effects of finite dimensions, collective excitations, meson exchange currents, short-range correlations, and final state interactions. These effects strongly modify the relativistic Fermi gas scaling functions, but they conserve the scaling properties. We used the scaling functions to predict electron and neutrino cross sections and we tested their validity by comparing them with the cross sections obtained with a full calculation. For electron scattering we also made a comparison with data. We have calculated the total charge-exchange neutrino cross sections for neutrino energies up to 300 MeV.

The nucleus-nucleus potential for the fusion reactions ${}^{40}\mathrm{Ca}+{}^{48}\mathrm{Ca}$, ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$, and ${}^{48}\mathrm{Ca}+{}^{48}\mathrm{Ca}$ has been calculated using the Monte Carlo method. The results obtained indicate that the technique employed for the calculation of the nucleus-nucleus potential is an efficient one. The effects of the spin and the isospin terms have also been studied using the same technique. The analysis of the results obtained for the ${}^{48}\mathrm{Ca}+{}^{48}\mathrm{Ca}$ reaction reveal that the isospin-dependent term in the nucleon-nucleon potential causes the nuclear potential to drop by an amount of 0.5 MeV. The analytical calculations of the fusion cross section, particularly those at energies less than the fusion barrier, are in good agreement with the experimental data. In these calculations the effective nucleon-nucleon potential chosen is of the M3Y-Paris potential form and no adjustable parameter has been used.

Electron captures on nuclei play an important role in the collapse of stellar core in the stages leading to a type-II supernova. Recent observations of subluminous Type II-P supernovae (e.g., 2005cs, 2003gd, 1999br) were able to rekindle the interest in 8–10 $M_{\odot }$ which develop O+Ne+Mg cores. We used the proton-neutron quasiparticle random phase approximation (pn-QRPA) theory to calculate the $B$(GT) strength for ${}^{24}\mathrm{Mg}$ $\to$${}^{24}\mathrm{Na}$ and its associated electron capture rates for incorporation in simulation calculations. The calculated rates, in this article, have differences with the earlier reported shell model and Fuller, Fowler, and Newman [2] (hereafter F${}^2\mathrm{N}$) rates. We compared Gamow-Teller (GT) strength distribution functions and found fairly good agreement with experiment and shell model. However, the GT centroid and the total GT strength, which are useful in the calculation of electron capture rates in the core of massive presupernova stars, lead to the enhancement of our rate up to a factor of 4 compared to the shell model rates at high temperatures and densities.

The quark matter equation of state (EoS) derived from the standard Nambu-Jona-Lasinio (NJL) model is soft enough to render neutron stars (NS) unstable at the onset of the deconfined phase, and no pure quark matter can be actually present in its interior. Since this is a peculiarity of the NJL model, we have studied a modified NJL model with a momentum cutoff which depends on the density. This procedure, which improves the agreement between QCD and NJL model at large density, modifies the standard NJL equation of state, and then it is potentially relevant for the stability analysis of neutron stars. We show that also within this approach, the NS instability still persists, and that the vacuum pressure, as a signal of quark confinement, has a fundamental role for the NS stability. In this respect, our conclusions point to a relationship between confinement and NS stability.

The density dependence of the symmetry energy in the equation of state of isospin asymmetric nuclear matter is studied using the isoscaling of the fragment yields and the antisymmetrized molecular dynamic calculation. It is observed that the experimental data at low densities are consistent with the form of symmetry energy, ${\mathrm{E}}_{\mathrm{sym}}\approx 31.6(\rho /{\rho }_{○}){}^{0.69}$, in close agreement with those predicted by the results of variational many-body calculation. A comparison of the present result with those reported recently using the NSCL-MSU data suggests that the heavy ion studies favor a dependence of the form, ${\mathrm{E}}_{\mathrm{sym}}\approx 31.6(\rho /{\rho }_{○}){}^{\gamma }$, where $\gamma =0.6-1.05$. This constrains the form of the density dependence of the symmetry energy at higher densities, ruling out an extremely “stiff” and “soft” dependences.

We report charged particle pair correlation analyses in the space of $\Delta \varphi$ (azimuth) and $\Delta \eta$ (pseudorapidity), for central Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV in the STAR detector. The analysis involves unlike-sign charged pairs and like-sign charged pairs, which are transformed into charge-dependent (CD) signals and charge-independent (CI) signals. We present detailed parametrizations of the data. A model featuring dense gluonic hot spots as first proposed by Van Hove predicts that the observables under investigation would have sensitivity to such a substructure should it occur, and the model also motivates selection of transverse momenta in the range $0.8<p_t<2.0$ GeV/$c$. Both CD and CI correlations of high statistical significance are observed, and possible interpretations are discussed.

The puzzle concerning the nucleosynthetic origin of ${}^{19}\mathrm{F}$ has been a topic of much interest in astrophysics. After the observation of an overabundance of ${}^{19}\mathrm{F}$ in thermally pulsing asymptotic giant branch (AGB) stars, attention has been drawn to the He shell flash, characteristic of these stars, as a possible site of fluorine synthesis. As the He intershell of AGBs is also known to undergo periods of high neutron exposure, ${}^{19}\mathrm{F}$ synthesized in this zone would be in danger of destruction by ${}^{19}\mathrm{F}$($n,\gamma$)${}^{20}\mathrm{F}$. The current recommended value of the Maxwellian averaged cross section (MACS) is uncertain by 20% in a temperature region corresponding to the He flash, which is insufficient for accurate stellar modeling. A measurement of the cross section has been performed at the Karlsruhe 3.7 MV Van de Graaff accelerator by cyclic activation of fluorine samples in a quasistellar neutron spectrum with a mean thermal energy of $\mathit{kT}=25$ keV. The new MACS at $\mathit{kT}=25$ keV is 44% lower and six times more accurate than reported previously.

We develop a variational theory of hot nuclear matter in neutron stars and supernovae. It can also be used to study charged, hot nuclear matter which may be produced in heavy-ion collisions. This theory is a generalization of the variational theory of cold nuclear and neutron star matter based on realistic models of nuclear forces and pair correlation operators. The present approach uses microcanonical ensembles and the variational principle obeyed by the free energy. In this paper we show that the correlated states of the microcanonical ensemble at a given temperature $T$ and density ρ can be orthonormalized preserving their diagonal matrix elements of the Hamiltonian. This allows for the minimization of the free energy without corrections from the nonorthogonality of the correlated basis states, similar to that of the ground state energy. Samples of the microcanonical ensemble can be used to study the response, and the neutrino luminosities and opacities of hot matter. We present methods to orthonormalize the correlated states that contribute to the response of hot matter.

We analyze fusion cross sections induced by the ${}^6\mathrm{He}$ halo projectile in the framework of the double-folding São Paulo potential, which has already been shown to be a reliable potential for the analysis of fusion cross sections induced by stable weakly bound nuclei. The results show that the fusion cross sections of ${}^6\mathrm{He}+{}^{209}\mathrm{Bi}$, ${}^{238}\mathrm{U}$, ${}^{64}\mathrm{Zn}$ are suppressed at energies above the barrier when compared with coupled-channels calculations that do not take into account the projectile breakup, whereas they are in agreement with the calculations at subbarrier energies. The results for the ${}^6\mathrm{He}+{}^{209}\mathrm{Bi}$ system are contradictory to those reported previously.

New measurements of the spin structure functions of the proton and deuteron $g_1^p(x,Q^2)$ and $g_1^d(x,Q^2)$ in the nucleon resonance region are compared with extrapolations of target-mass-corrected next-to-leading-order (NLO) QCD fits to higher energy data. Averaged over the entire resonance region ($W<2$ GeV), the data and QCD fits are in good agreement in both magnitude and $Q^2$ dependence for $Q^2>1.7$ GeV${}^2/c^2$. This “global” duality appears to result from cancellations among the prominent “local” resonance regions: in particular strong ${\sigma }_{3/2}$ contributions in the $\Delta (1232)$ region appear to be compensated by strong ${\sigma }_{1/2}$ contributions in the resonance region centered on 1.5 GeV. These results are encouraging for the extension of NLO QCD fits to lower $W$ and $Q^2$ than have been used previously.

We study the phase structure and condensates of two-flavor QCD at finite isospin chemical potential in the framework of a confining, Dyson-Schwinger equation model. We find that the pion superfluidity phase is favored at high enough isospin chemical potential. A new gauge-invariant mixed quark-gluon condensate induced by isospin chemical potential is proposed based on operator product expansion. We investigate the sign and magnitude of this new condensate and show that it is an important condensate in QCD sum rules at finite isospin density.

Dispersion relations provide a powerful tool to analyze the electromagnetic form factors of the nucleon for all momentum transfers. Constraints from meson-nucleon scattering data, unitarity, and perturbative quantum chromodynamics (QCD) can be included in a straightforward way. In particular, we include the $2\pi ,\rho \pi$, and $K\overline{K}$ continua as independent input in our analysis and provide an error band for our results. Moreover, we discuss two different methods to include the asymptotic constraints from perturbative QCD. We simultaneously analyze the world data for all four form factors in both the spacelike and timelike regions and generally find good agreement with the data. We also extract the nucleon radii and the $\omega \mathit{NN}$ coupling constants. For the radii, we generally find good agreement with other determinations with the exception of the electric charge radius of the proton, which comes out smaller. The $\omega \mathit{NN}$ vector coupling constant is determined relatively well by the fits, but for the tensor coupling constant even the sign cannot be determined.