46,039 research outputs found

    Links Between Heavy Ion and Astrophysics

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    Heavy ion experiments provide important data to test astrophysical models. The high density equation of state can be probed in HI collisions and applied to the hot protoneutron star formed in core collapse supernovae. The Parity Radius Experiment (PREX) aims to accurately measure the neutron radius of 208^{208}Pb with parity violating electron scattering. This determines the pressure of neutron rich matter and the density dependence of the symmetry energy. Competition between nuclear attraction and coulomb repulsion can form exotic shapes called nuclear pasta in neutron star crusts and supernovae. This competition can be probed with multifragmentation HI reactions. We use large scale semiclassical simulations to study nonuniform neutron rich matter in supernovae. We find that the coulomb interactions in astrophysical systems suppress density fluctuations. As a result, there is no first order liquid vapor phase transition. Finally, the virial expansion for low density matter shows that the nuclear vapor phase is complex with significant concentrations of alpha particles and other light nuclei in addition to free nucleons.Comment: 8 pages, 6 figures. To be published in "Dynamics and Thermodynamics with Nucleon Degrees of Freedom", eds. P. Chomaz, F. Gulminelli, J. Natowitz, and S. Yennello, http://cyclotron.tamu.edu/wci3/wci_book.htm

    Parity Violation in Astrophysics

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    Core collapse supernovae are gigantic explosions of massive stars that radiate 99% of their energy in neutrinos. This provides a unique opportunity for large scale parity or charge conjugation violation. Parity violation in a strong magnetic field could lead to an asymmetry in the neutrino radiation and recoil of the newly formed neutron star. Charge conjugation violation in the neutrino-nucleon interaction reduces the ratio of neutrons to protons in the neutrino driven wind above the neutron star. This is a problem for r-process nucleosynthesis in this wind. On earth, parity violation is an excellent probe of neutrons because the weak charge of a neutron is much larger than that of a proton. The Parity Radius Experiment (PREX) at Jefferson Laboratory aims to precisely measure the neutron radius of 208^{208}Pb with parity violating elastic electron scattering. This has many implications for astrophysics, including the structure of neutron stars, and for atomic parity nonconservation experiments.}Comment: 4 pages, 2 figures, proceedings of PAVI04 conference in Grenoble, Franc

    Weakness or Strength in the Golden Years of RHIC and LHC?

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    Recent LHC data suggest that perturbative QCD provides a qualitatively consistent picture of jet quenching. Constrained to RHIC pi0 suppression, zero parameter WHDG energy loss predictions agree quantitatively with the charged hadron v2 and D meson RAA measured at LHC and qualitatively with the charged hadron RAA. On the other hand, RHIC-constrained LHC predictions from fully strongly-coupled AdS/CFT qualitatively oversuppress D mesons compared to data; light meson predictions are on less firm theoretical ground but also suggest oversuppression. More detailed data from heavy, especially B, mesons will continue to help clarify our picture of the physics of the quark-gluon plasma. Since the approach of pQCD predictions to LHC data occurs at momenta >~ 15 GeV/c, a robust consistency check between pQCD and both RHIC and LHC data requires RHIC jet measurements.Comment: 4 pages. 3 figures. Proceedings for Hard Probes 2012. Minor grammatical and reference changes from v

    Remarks on the instability of black Dp-branes

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    We show that for black Dpp-branes having charge QQ and Hawking temperature TT, the product QT7‚ąípQT^{7-p} is bounded from above for p‚ȧ5p\leq 5 and is unbounded for p=6p=6. While the maximum occurs at some finite value of a parameter for p‚ȧ4p \leq 4, it occurs at infinity of the parameter for p=5p=5. As a consequence, for fixed charge, there are two black Dpp-branes (for p‚ȧ4p\leq 4) at any given temperature less than its maximum value, and when the temperature is maximum there is one black Dpp-brane. For p=5p=5, there is only one black D5-brane at a given temperature less than its maximum value, whereas, for p=6p=6, since there is no bound for the temperature, there is always a black D6-brane solution at a given temperature. Of the two black Dpp-branes (for p‚ȧ4p\leq 4), one is large which is shown to be thermodynamically unstable and the other is small which is stable. But for p=5,6p=5,6, the black Dpp-branes are always thermodynamically unstable. The stable, small black Dpp-brane, however, under certain conditions, can become unstable quantum mechanically and decay either to a BPS Dpp-brane or to a Kaluza-Klein "bubble of nothing" through closed string tachyon condensation. The small D5, D6 branes, although classically unstable, have the same fate under similar conditions.Comment: 12 pages, LaTeX, 1 figure, v2: minor clarifications added, v3: added free energy calculation, version to appear in Phys. Lett.

    Parity Violation, the Neutron Radius of Lead, and Neutron Stars

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    The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties in the reaction mechanism. The Parity Radius Experiment at the Jefferson Laboratory offers an attractive electro-weak alternative to the hadronic program and promises to measure the neutron radius of 208Pb accurately and model independently via parity-violating electron scattering. In this contribution we examine the far-reaching implications that such a determination will have in areas as diverse as nuclear structure, atomic parity violation, and astrophysics.Comment: 5 pages, 5 figures, proceedings to the PAVI06 conferenc

    From Dreaming to Living

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