12,948 research outputs found
Scattering of Dirac and Majorana Fermions off Domain Walls
We investigate the interaction of fermions having both Dirac and left-handed
and right-handed Majorana mass terms with vacuum domain walls. By solving the
equations of motion in thin-wall approximation, we calculate the reflection and
transmission coefficients for the scattering of fermions off walls.Comment: 6 pages, 1 figure, some typos corrected, one reference added, major
revisions, title changed, version accepted for publication in Phys. Rev.
Partonic effects on anisotropic flows at RHIC
We report recent results from a multiphase transport (AMPT) model on the
azimuthal anisotropies of particle momentum distributions in heavy ion
collisions at the Relativistic Heavy Ion Collider. These include higher-order
anisotropic flows and their scaling, the rapidity dependence of anisotropic
flows, and the elliptic flow of charm quarks.Comment: 7 pages, 5 figures, talk given at "Hot Quarks 2004", July 18-24,
2004, Taos Valley, NM, US
Non-thermal leptogenesis with strongly hierarchical right handed neutrinos
Assuming the Dirac-type neutrino masses m_D are related to quark or charged
lepton masses, neutrino oscillation data indicate that right handed neutrino
masses are in general strongly hierarchical. In particular, if m_D is similar
to the up-type quark masses, the mass of the lightest right handed neutrino
M_1<~10^6 GeV. We show that non-thermal leptogenesis by inflaton decay can
yield sufficient baryon asymmetry despite this constraint, and discuss how the
asymmetry is correlated with the low energy neutrino masses and CP-violating
phases.Comment: 7 pages, 5 figures. v2: added some comments and references, v3: minor
corrections and additions, v4: a typo corrected, published versio
Thermodynamics of (2+1)-flavor QCD: Confronting Models with Lattice Studies
The Polyakov-quark-meson (PQM) model, which combines chiral as well as
deconfinement aspects of strongly interacting matter is introduced for three
light quark flavors. An analysis of the chiral and deconfinement phase
transition of the model and its thermodynamics at finite temperatures is given.
Three different forms of the effective Polyakov loop potential are considered.
The findings of the (2+1)-flavor model investigations are confronted to
corresponding recent QCD lattice simulations of the RBC-Bielefeld, HotQCD and
Wuppertal-Budapest collaborations. The influence of the heavier quark masses,
which are used in the lattice calculations, is taken into account. In the
transition region the bulk thermodynamics of the PQM model agrees well with the
lattice data.Comment: 13 pages, 7 figures, 3 tables; minor changes, final version to appear
in Phys. Rev.
An Open Inflationary Model for Dimensional Reduction and its Effects on the Observable Parameters of the Universe
Assuming that higher dimensions existed in the early stages of the universe
where the evolution was inflationary, we construct an open, singularity-free,
spatially homogeneous and isotropic cosmological model to study the effects of
dimensional reduction that may have taken place during the early stages of the
universe. We consider dimensional reduction to take place in a stepwise manner
and interpret each step as a phase transition. By imposing suitable boundary
conditions we trace their effects on the present day parameters of the
universe.Comment: 5 pages, accepted for publication in Int. J. of Mod. Phys.
On the Search for the Amino Acids on the Lunar Surface as it Relates to Other Extraterrestrial Bodies
The early search for the amino acids on the lunar surface fines indicated such a low amount of the amino acids that it was deemed insignifi cant. While the later studies seemed to depart in some ways from the earlier results, they were not pursued. In this paper we critically ev aluate the results from the Apollo missions from the new perspective with considerations of the sensitivity of the instrumentation availabl e at the time. We discuss the possible relevance of the lunar results to the findings of the amino acids on the surfaces of other extraterrestrial bodies, such as Mars
Stabilizing quantum metastable states in a time-periodic potential
Metastability of a particle trapped in a well with a time-periodically
oscillating barrier is studied in the Floquet formalism. It is shown that the
oscillating barrier causes the system to decay faster in general. However,
avoided crossings of metastable states can occur with the less stable states
crossing over to the more stable ones. If in the static well there exists a
bound state, then it is possible to stabilize a metastable state by
adiabatically increasing the oscillating frequency of the barrier so that the
unstable state eventually cross-over to the stable bound state. It is also
found that increasing the amplitude of the oscillating field may change a
direct crossing of states into an avoided one.Comment: 7 pages, 6 figure
Transverse-Mass Spectra in Heavy-Ion Collisions at energies E_{lab} = 2--160 GeV/nucleon
Transverse-mass spectra of protons, pions and kaons produced in collisions of
heavy nuclei are analyzed within the model of 3-fluid dynamics. It was
demonstrated that this model consistently reproduces these spectra in wide
ranges of incident energies E_{lab}, from 4A GeV to 160A GeV, rapidity bins and
centralities of the collisions. In particular, the model describes the
"step-like" dependence of kaon inverse slopes on the incident energy. The key
point of this explanation is interplay of hydrodynamic expansion of the system
with its dynamical freeze-out.Comment: 13 pages, 16 figures, summary is extended, version accepted by Phys.
Rev.
Validation Through Simulations of a Cn2 Profiler for the ESO/VLT Adaptive Optics Facility
The Adaptive Optics Facility (AOF) project envisages transforming one of the
VLT units into an adaptive telescope and providing its ESO (European Southern
Observatory) second generation instruments with turbulence corrected
wavefronts. For MUSE and HAWK-I this correction will be achieved through the
GALACSI and GRAAL AO modules working in conjunction with a 1170 actuators
Deformable Secondary Mirror (DSM) and the new Laser Guide Star Facility
(4LGSF). Multiple wavefront sensors will enable GLAO and LTAO capabilities,
whose performance can greatly benefit from a knowledge about the stratification
of the turbulence in the atmosphere. This work, totally based on end-to-end
simulations, describes the validation tests conducted on a Cn2 profiler adapted
for the AOF specifications. Because an absolute profile calibration is strongly
dependent on a reliable knowledge of turbulence parameters r0 and L0, the tests
presented here refer only to normalized output profiles. Uncertainties in the
input parameters inherent to the code are tested as well as the profiler
response to different turbulence distributions. It adopts a correction for the
unseen turbulence, critical for the GRAAL mode, and highlights the effects of
masking out parts of the corrected wavefront on the results. Simulations of
data with typical turbulence profiles from Paranal were input to the profiler,
showing that it is possible to identify reliably the input features for all the
AOF modes.Comment: 15 pages, 12 figures, accepted for publication in the MNRAS Accepted
2015 January 22. Received 2015 January 21; in original form 2014 December
Gamma-rays from ultracompact minihalos: potential constraints on the primordial curvature perturbation
Ultracompact minihalos (UCMHs) are dense dark matter structures which can
form from large density perturbations shortly after matter-radiation equality.
If dark matter is in the form of Weakly Interacting Massive Particles (WIMPs),
then UCMHs may be detected via their gamma-ray emission. We investigate how the
{\em{Fermi}} satellite could constrain the abundance of UCMHs and place limits
on the power spectrum of the primordial curvature perturbation. Detection by
{\em Fermi} would put a lower limit on the UCMH halo fraction. The smallest
detectable halo fraction, , is for . If gamma-ray emission from UCMHs is not detected, an
upper limit can be placed on the halo fraction. The bound is tightest, , for . The
resulting upper limit on the power spectrum of the primordial curvature
perturbation in the event of non-detection is in the range on scales . This is substantially tighter than the existing constraints from
primordial black hole formation on these scales, however it assumes that dark
matter is in the form of WIMPs and UCMHs are not disrupted during the formation
of the Milky Way halo.Comment: 5 pages, 2 figures, version to appear in Phys. Rev. D, minor change
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