Strongly Interacting Matter at Finite Chemical Potential : Hybrid Model Approach

Search for a proper and realistic equation of state (EOS) for strongly interacting matter used in the study of the QCD phase diagram still appears as a challenging problem. Recently, we constructed a hybrid model description for the quark gluon plasma (QGP) as well as hadron gas (HG) phases where we used an excluded volume model for HG and a thermodynamically consistent quasiparticle model for the QGP phase. The hybrid model suitably describes the recent lattice results of various thermodynamical as well as transport properties of the QCD matter at zero baryon chemical potential ($\mu_{B}$). In this paper, we extend our investigations further in obtaining the properties of QCD matter at finite value of $\mu_{B}$ and compare our results with the most recent results of lattice QCD calculation.Comment: 14 pages, 9 figure

QCD Phase Transition in a new Hybrid Model Formulation

Search of a proper and realistic equations of state (EOS) for strongly interacting matter used in the study of QCD phase diagram still appears as a challenging task. Recently, we have constructed a hybrid model description for the quark gluon plasma (QGP) as well as hadron gas (HG) phases where we use a new excluded-volume model for HG and a thermodynamically-consistent quasiparticle model for the QGP phase. We attempt to use them to get a QCD phase boundary and a critical point. We test our hybrid model by reproducing the entire lattice QCD data for strongly interacting matter at zero baryon chemical potential ($\mu_{B}$)and predict the results at finite $\mu_{B}$ and $T$.Comment: 5 pages, 4 figures, to be published in proceedings of QGP MEET 2012 held at VECC, Kolkata, INDI

Critical Point on the QCD Deconfining Phase Boundary

Ambiguities regarding the physics and the existence of the critical point (CP) on the QCD phase boundary still exist and the mist regarding the conjectured QCD phase boundary has not yet cleared. In this paper we extend our earlier study where we constructed a deconfining phase boundary using Gibbs' equilibrium conditions after using a quasiparticle equation of state (EOS) for quark gluon plasma (QGP) and an excluded volume EOS for the hadron gas (HG) and find the presence of a critical point on this phase boundary where the first order phase transition terminates. In this paper, we plot the difference in the normalized entropy density ($s/T^{3}$) between HG and QGP phases along the deconfining phase boundary and find that it vanishes at CP. Further we have shown the variation of the square of speed of sound ($c_{s}^{2}$) for the HG and QGP separately and find that the difference ($\Delta c_{s}^{2}$) between them along the deconfining phase boundary again vanishes at the CP of the boundary. We also plot the variation of shear viscosity to entropy density ratio ($\eta/s$) in HG as well as in QGP phases separately with respect to temperature at different baryonic chemical potential ($\mu_{B}$). The presence of a cusp like structure in $\eta/s$ again confirms the existence of CP on the deconfining phase boundary as predicted by some authors. These studies thus firmly indicate the precise location of CP as a second order phase transition point.Comment: 15 pages, 4 figure

Holographic Dark Energy Model in Brans-Dicke Theory with Future Event Horizon

In this paper, we study the dynamics of non-interacting and interacting holographic dark energy models in the framework of Brans-Dicke theory. As system's infra-red cut-off we consider the future event horizon. The motivation of this work is to use the logarithmic form of the Brans-Dicke scalar field, $\phi \propto ln(\alpha+\beta a)$, where $\alpha$ and $\beta$ are constants and `a' is the scalar factor as proposed Kumar and Singh in a recent work to study the new agegraphic dark energy models. We find the time-dependent equation of state parameter and deceleration parameter which describe the phase transition of the universe. We observe that the model explains the early time inflation and late time acceleration including matter-dominated phase. It is also observed that the equation of state parameter may cross phantom divide line in late time evolution. The cosmic coincidence problem is also discussed for both the models. We observe that this logarithmic form of Brans-Dicke scalar field is more appropriate to achieve a less acute coincidence problem in non-interacting model whereas a soft coincidence can be achieved if coupling parameter in interacting model has small value.Comment: 11 Page

Large scale shell model calculations for even-even 62−66^{62-66}Fe isotopes

The recently measured experimental data of Legnaro National Laboratories on neutron rich even isotopes of $^{62-66}$Fe with A=62,64,66 have been interpreted in the framework of large scale shell model. Calculations have been performed with a newly derived effective interaction GXPF1A in full $\it{fp}$ space without truncation. The experimental data is very well explained for $^{62}$Fe, satisfactorily reproduced for $^{64}$Fe and poorly fitted for $^{66}$Fe. The increasing collectivity reflected in experimental data when approaching N=40 is not reproduced in calculated values. This indicates that whereas the considered valence space is adequate for $^{62}$Fe, inclusion of higher orbits from $\it{sdg}$ shell is required for describing $^{66}$Fe.Comment: 10 pages, 6 figure

Structure of odd 79,81,83^{79,81,83}Se isotopes with proton and neutron excitations across Z=28Z=28 AND N=40N= 40

The recently measured experimental data of $^{79,81,83}$Se isotopes have been interpreted in terms of shell model calculations. The calculations have been performed in ${f_{5/2}pg_{9/2}}$ space with the recently derived interactions, namely with JUN45 and jj44b. To study the importance of the proton excitations across the $Z=28$ shell in this region. We have also performed calculation in ${fpg_{9/2}}$ valence space using an ${fpg}$ effective interaction with $^{48}$Ca core and imposing a truncation. Excitation energies, $B(2)$ values, quadrupole moments and magnetic moments are compared with experimental data when available. Present study reveals the importance of proton excitations across the $Z=28$ shell for predicting quadrupole and magnetic moments.Comment: 12 pages, 6 figures. arXiv admin note: text overlap with arXiv:1210.579

Structure of odd Ge isotopes with 40<N<5040 < N < 50

We have interpreted recently measured experimental data of $^{77}$Ge, and also for $^{73,75,79,81}$Ge isotopes in terms of state-of-the-art shell model calculations. Excitation energies, B(2) values, quadrupole moments and magnetic moments are compared with experimental data when available. The calculations have been performed with the recently derived interactions, namely with JUN45 and jj44b for ${f_{5/2}pg_{9/2}}$ space. We have also performed calculation for ${fpg_{9/2}}$ valence space using an ${fpg}$ effective interaction with $^{48}$Ca core and imposing a truncation to study the importance of the proton excitations across the Z=28 shell in this region. The predicted results of jj44b interaction are in good agreement with experimental data.Comment: 22 pages, 7 figures, Physics of Atomic Nucle

Comparison of shell model results for even-even Se isotopes

Comprehensive set of shell model calculations for $^{78-84}$Se isotopes have been performed with recently derived interactions, namely JUN45 and jj44b for ${f_{5/2}pg_{9/2}}$ space. To study the importance of the proton excitations across Z=28 shell in this region mentioned by Cheal {\it et al.} [Phys. Rev. Lett. {\bf104}, 252502 (2010)], calculation for ${fpg_{9/2}}$ valence space using an ${fpg}$ effective interaction with $^{48}$Ca as core and imposing a truncation has also been performed. Comparison of the calculations with experimental data show that the predicted results of jj44b interaction are in good agreement with experimental data.Comment: 15 pages, 6 figures, Accepted for publication in Physica Script

Shell-model results in fpfp and fpg9/2{fpg_{9/2}} spaces for 61,63,65^{61,63,65}Co isotopes

Low-lying spectra and several high-spin states of odd--even $^{61,63,65}$Co isotopes are calculated in two different shell-model spaces. First set of calculations have been carried out in ${fp}$ shell valence space (full $fp$ space for $^{63,65}$Co and a truncated one for $^{61}$Co) using two recently derived ${fp}$ shell interactions, namely GXPF1A and KB3G, with $^{40}$Ca as core. Similarly, the second set of calculations have been performed in ${fpg_{9/2}}$ valence space using an ${fpg}$ effective interaction due to Sorlin {\it et al}., with $^{48}$Ca as core and imposing a truncation. It is seen that the results of GXPF1A and KB3G are reasonable for $^{61,63}$Co. For $^{65}$Co, shell-model results show that the ${fpg}$ interaction adopted in the study is inadequate and also point out that it is necessary to include orbitals higher than $1g_{9/2}$ for neutron-rich Co isotopes.Comment: 19 pages, 3 figures, accepted for publication in Physics of Atomic Nucle

Nuclear β−\beta^--decay half-lives for fpfp and fpgfpg shell nuclei

In the present work we calculate the allowed $\beta^-$-decay half-lives of nuclei with $Z = 20 -30$ and N $\leq$ 50 systematically under the framework of the nuclear shell model. A recent study shows that some nuclei in this region belong to the island of inversion. We perform calculation for $fp$ shell nuclei using KB3G effective interaction. In the case of Ni, Cu, and Zn, we used JUN45 effective interaction. Theoretical results of $Q$ values, half-lives, excitation energies, log$ft$ values, and branching fractions are discussed and compared with the experimental data. In the Ni region, we also compared our calculated results with recent experimental data [Z. Y. Xu {\it et al.}, \emph{Phys. Rev. Lett.} \textbf{113}, 032505, 2014]. Present results agree with the experimental data of half-lives in comparison to QRPA.Comment: Accepted in Journal of Physics G: Nuclear and Particle Physic