6,549 research outputs found
Chain configurations in light nuclei
The model of nuclear matter built from alpha-particles is proposed. The
strong deformed shape for doubly even N=Z nuclides from carbon to magnesium has
been determined according to this model. In this paper we undertake very simple
approach, which assumes the existence of low lying chain configurations.Comment: 6 pages, 5 figure
Influence of trapping potentials on the phase diagram of bosonic atoms in optical lattices
We study the effect of external trapping potentials on the phase diagram of
bosonic atoms in optical lattices. We introduce a generalized Bose-Hubbard
Hamiltonian that includes the structure of the energy levels of the trapping
potential, and show that these levels are in general populated both at finite
and zero temperature. We characterize the properties of the superfluid
transition for this situation and compare them with those of the standard
Bose-Hubbard description. We briefly discuss similar behaviors for fermionic
systems.Comment: 4 pages, 3 figures; final version, to be published in Phys. Rev.
Unlike particle correlations and the strange quark matter distillation process
We present a new technique for observing the strange quark matter
distillation process based on unlike particle correlations. A simulation is
presented based on the scenario of a two-phase thermodynamical evolution model.Comment: 15 pages, 2 figures, 1 tabl
Macroscopic dynamics of a trapped Bose-Einstein condensate in the presence of 1D and 2D optical lattices
The hydrodynamic equations of superfluids for a weakly interacting Bose gas
are generalized to include the effects of periodic optical potentials produced
by stationary laser beams. The new equations are characterized by a
renormalized interaction coupling constant and by an effective mass accounting
for the inertia of the system along the laser direction. For large laser
intensities the effective mass is directly related to the tunneling rate
between two consecutive wells. The predictions for the frequencies of the
collective modes of a condensate confined by a magnetic harmonic trap are
discussed for both 1D and 2D optical lattices and compared with recent
experimental data.Comment: 4 pages, 2 postscript figure
Spin and Pseudospin symmetries in the Dirac equation with central Coulomb potentials
We analyze in detail the analytical solutions of the Dirac equation with
scalar S and vector V Coulomb radial potentials near the limit of spin and
pseudospin symmetries, i.e., when those potentials have the same magnitude and
either the same sign or opposite signs, respectively. By performing an
expansion of the relevant coefficients we also assess the perturbative nature
of both symmetries and their relations the (pseudo)spin-orbit coupling. The
former analysis is made for both positive and negative energy solutions and we
reproduce the relations between spin and pseudospin symmetries found before for
nuclear mean-field potentials. We discuss the node structure of the radial
functions and the quantum numbers of the solutions when there is spin or
pseudospin symmetry, which we find to be similar to the well-known solutions of
hydrogenic atoms.Comment: 9 pages, 2 figures, uses revte
The long gamma-ray burst rate and the correlation with host galaxy properties
To answer questions on the start and duration of the epoch of reionisation,
periods of galaxy mergers and properties of other cosmological encounters, the
cosmic star formation history (CSFH), is of fundamental importance. Using the
association of long gamma-ray bursts (LGRBs) with the death of massive stars
and their ultra-luminous nature, the CSFH can be probed to higher redshifts
than current conventional methods. Unfortunately, no consensus has been reached
on the manner in which the LGRB rate (LGRBR) traces the CSFH, leaving many of
the questions mentioned mostly unexplored by this method. Observations by the
GRB NIR detector (GROND) over the past 4 years have, for the first time,
acquired highly complete LGRB samples. Driven by these completeness levels and
new evidence of LGRBs also occurring in more massive and metal rich galaxies
than previously thought, the possible biases of the LGRBR-CSFH connection are
investigated over a large range of galaxy properties. The CSFH is modelled
using empirical fits to the galaxy mass function and galaxy star formation
rates. Biasing the CSFH by metallicity cuts, mass range boundaries, and other
unknown redshift dependencies, a LGRBR is generated and compared to the highly
complete GROND sample. It is found that there is no strong preference for a
metallicity cut or fixed galaxy mass boundaries and that there are no unknown
redshift effects, in contrast to previous work which suggest values of
Z/Z_sun~0.1-0.3. From the best-fit models, we predict that ~1.2% of the LGRB
burst sample exists above z=6. The linear relationship between the LGRBR and
the CSFH suggested by our results implies that redshift biases present in
previous LGRB samples significantly affect the inferred dependencies of LGRBs
on their host galaxy properties. Such biases can lead to, e.g., an
interpretation of metallicity limitations and evolving LGRB luminosity
functions.Comment: 15 pages, 14 figures, 7 tables, accepted for publication in Astronomy
& Astrophysic
Higgs boson pair production in gluon fusion at NLO with full top-quark mass dependence
We present the calculation of the cross section and invariant mass
distribution for Higgs boson pair production in gluon fusion at next-to-leading
order (NLO) in QCD. Top-quark masses are fully taken into account throughout
the calculation. The virtual two-loop amplitude has been generated using an
extension of the program GoSam supplemented with an interface to Reduze for the
integral reduction. The occurring integrals have been calculated numerically
using the program SecDec. Our results, including the full top-quark mass
dependence for the first time, allow us to assess the validity of various
approximations proposed in the literature, which we also recalculate. We find
substantial deviations between the NLO result and the different approximations,
which emphasizes the importance of including the full top-quark mass dependence
at NLO.Comment: Version published in PRL, v2: results at 13 TeV (v1 was at 14 TeV),
minor correction to virtual part included, conclusions unchange
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