121404062
First Measurement of Parity-Nonconserving Neutron-Spin Rotation: The Tin Isotopes
A parity-nonconserving (PNC) neutron-spin rotation, ${\ensuremath{\phi}}_{\mathrm{PNC}}$, for neutrons passing through matter due, presumably, to the weak interaction is observed for the first time. For tin isotopes, the following values for ${\ensuremath{\phi}}_{\mathrm{PNC}}$ in ${10}^{\ensuremath{-}6}$ rad/cm are found: $^{124}\mathrm{Sn}$, +0.48\ifmmode\pm\else\textpm\fi{}1.49; $^{117}\mathrm{Sn}$, +36.7\ifmmode\pm\else\textpm\fi{}2.7; and natural Sn, +4.95\ifmmode\pm\else\textpm\fi{}0.93, with the positive sign corresponding to a right-handed rotation about the momentum. Evidence in $^{117}\mathrm{Sn}$ for a larger total cross section for positive-helicity neutrons than for negative-helicity ones is also reported.
122190148
A mass-selecting apparatus to measure the energy loss of fission fragments in gases
Abstract We describe an apparatus combining solid-state and gas ionization chamber techniques to measure — for both fragments released in a fission event — the energy lost in a given gaseous range and the residual energy. This device allows to measure the energy loss in gases of fission fragments selecting their masses The performances of the apparatus are discussed referring to the data obtained by slowing down fission fragments from 252 Cf in gaseous argon.
122896950
Measurement of parity nonconserving neutron spin rotation in lanthanum
The rotation, phi/sub pnc/, of a neutron beam polarization vector due to parity nonconserving forces is measured in a lanthanum target. It is found that phi/sub pnc//l = -(21.9 +- 2.9) x 10- /sup 5/ rad/cm, where the negative sign corresponds to a left-handed rotation of the neutron spin about its momentum.
119208307
CROSSING THE PHANTOM DIVIDE WITH k-ESSENCE IN BRANEWORLDS
We study a flat 3-brane in presence of a linear k field with nonzero cosmological constant �4. In this model the crossing of the phantom divide (PD) occurs when the k-essence energy density becomes negative. We show that in the high energy regime the effective equation of state has a resemblance of a modified Chaplygin gas while in the low energy regime it becomes linear. We find a scale factor that begins from a singularity and evolves to a de Sitter stable stage while other solutions have a super-accelerated regime and end with a big rip. We use the energy conditions to show when the effective equation of state of the brane-universe crosses the PD.
119208212
Tachyon and Quintessence in Brane-Worlds
Using tachyon or quintessence fields along with a barotropic fluid on the brane we examine the different cosmological stages in a Friedmann-Robertson-Walker universe, from the first radiation scenario to the later era dominated by cosmic string networks. We introduce a new algorithm to generalize previous works on exact solutions and apply it to study tachyon and quintessence fields localized on the brane. We also explore the low and high energy regimes of the solutions. Besides, we show that the tachyon and quintessence fields are driven by an inverse power law potential. Finally, we find several simple exacts solutions for tachyon and/or quintessence fields.
119112732
Comments on Unified Dark Energy and Dark Matter from a Scalar Field Different from Quintessence
In a recent paper by C. Gao, M. Kunz, A. Liddle and D. Parkinson [arXiv:0912.0949], the unification of dark matter and dark energy was explored within a theory containing a scalar field of non-Lagrangian type. This scalar field, different from the classic quintessence, can be obtained from the scalar field representation of an interacting two-fluid mixture described in the paper by L.P. Chimento and M. Forte [arXiv:0706.4142]