32,693 research outputs found
Handedness of direct photons
The azimuthal asymmetry of direct photons originating from primary hard
scatterings between partons is calculated. This can be accounted for by the
inclusion of the color dipole orientation, which is sensitive to the rapid
variation of the nuclear profile. To this end we introduce the dipole
orientation within the saturation model of Golec-Biernat and W\"usthoff, while
preserving all its features at the cross-section level. We show that the direct
photon elliptic anisotropy v2 coming from this mechanism changes sign and
becomes negative for peripheral collisions, albeit it is quite small for
nuclear collisions at the RHIC energy.Comment: 6 pages, 6 figures, Based on talk given by A.H.R. at II LAWHEP, Sao
Miguel das Missoes, Brazil, December 3-7, 200
Coherent center domains from local Polyakov loops
We analyze properties of local Polyakov loops using quenched as well as
dynamical SU(3) gauge configurations for a wide range of temperatures. It is
demonstrated that for both, the confined and the deconfined regime, the local
Polyakov loop prefers phase values near the center elements 1, exp(i 2 pi/3),
exp(-i 2 pi/3). We divide the lattice sites into three sectors according to
these phases and show that the sectors give rise to the formation of clusters.
For a suitable definition of these clusters we find that in the quenched case
deconfinement manifests itself as the onset of percolation of the clusters. A
possible continuum limit of the center clusters is discussed
A bosonic Josephson junction controlled by a single trapped ion
We theoretically investigate the properties of a double-well bosonic
Josephson junction coupled to a single trapped ion. We find that the coupling
between the wells can be controlled by the internal state of the ion, which can
be used for studying mesoscopic entanglement between the two systems and to
measure their interaction with high precision. As a particular example we
consider a single Rb atom and a small Bose-Einstein condensate
controlled by a single Yb ion. We calculate inter-well coupling
rates reaching hundreds of Hz, while the state dependence amounts to tens of Hz
for plausible values of the currently unknown s-wave scattering length between
the atom and the ion. The analysis shows that it is possible to induce either
the self-trapping or the tunneling regime, depending on the internal state of
the ion. This enables the generation of large scale ion-atomic wavepacket
entanglement within current technology.Comment: 6 pages and 5 figures, including additional material. Accepted for
publication in Phys. Rev. Let
Quenching of high-pT hadrons: Energy Loss vs Color Transparency
High-pT hadrons produced in hard collisions and detected inclusively bear
peculiar features: (i) they originate from jets whose initial virtuality and
energy are of the same order; (ii) such jets are rare and have a very biased
energy sharing among the particles, namely, the detected hadron carries the
main fraction of the jet energy. The former feature leads to an extremely
intensive gluon radiation and energy dissipation at the early stage of
hadronization, either in vacuum or in a medium. As a result, a leading hadron
must be produced on a short length scale. Evaluation within a model of
perturbative fragmentation confirms the shortness of the production length.
This result is at variance with the unjustified assumption of long production
length, made within the popular energy loss scenario. Thus we conclude that the
main reason of suppression of high-pT hadrons in heavy ion collisions is the
controlled by color transparency attenuation of a high-pT dipole propagating
through the hot medium. Adjusting a single parameter, the transport
coefficient, we describe quite well the data from LHC and RHIC for the
suppression factor R_{AA} as function of pT, collision energy and centrality.
We observe that the complementary effect of initial state interaction causes a
flattening and even fall of R_{AA} at large pT. The azimuthal anisotropy of
hadron production, calculated with no further adjustment, also agrees well with
data at different energies and centralities.Comment: 17 pages, 19 figure
The Quantum Cosmological Wavefunction at Very Early Times for a Quadratic Gravity Theory
The quantum cosmological wavefunction for a quadratic gravity theory derived
from the heterotic string effective action is obtained near the inflationary
epoch and during the initial Planck era. Neglecting derivatives with respect to
the scalar field, the wavefunction would satisfy a third-order differential
equation near the inflationary epoch which has a solution that is singular in
the scale factor limit . When scalar field derivatives are included,
a sixth-order differential equation is obtained for the wavefunction and the
solution by Mellin transform is regular in the limit. It follows that
inclusion of the scalar field in the quadratic gravity action is necessary for
consistency of the quantum cosmology of the theory at very early times.Comment: Tex, 13 page
- …