232 research outputs found
Differences in the Cooling Behavior of Strange Quark Matter Stars and Neutron Stars
The general statement that hypothetical strange (quark matter) stars cool
more rapidly than neutron stars is investigated in greater detail. It is found
that the direct Urca process could be forbidden not only in neutron stars but
also in strange stars. In this case, strange stars are slowly cooling, and
their surface temperatures are more or less indistinguishable from those of
slowly cooling neutron stars. Furthermore the case of enhanced cooling is
reinvestigated. It shows that strange stars cool significantly more rapidly
than neutron stars within the first years after birth. This feature
could become particularly interesting if continued observation of SN 1987A
would reveal the temperature of the possibly existing pulsar at its center.Comment: 9 pages, LaTeX (aas-style file), 2 ps-figures. To be published in ApJ
Letter
Strangeness in Neutron Stars
It is generally agreed on that the tremendous densities reached in the
centers of neutron stars provide a high-pressure environment in which numerous
novel particles processes are likely to compete with each other. These
processes range from the generation of hyperons to quark deconfinement to the
formation of kaon condensates and H-matter. There are theoretical suggestions
of even more exotic processes inside neutron stars, such as the formation of
absolutely stable strange quark matter, a configuration of matter even more
stable than the most stable atomic nucleus, iron. In the latter event, neutron
stars would be largely composed of pure quark matter, eventually enveloped in a
thin nuclear crust. No matter which physical processes are actually realized
inside neutron stars, each one leads to fingerprints, some more pronounced than
others though, in the observable stellar quantities. This feature combined with
the unprecedented progress in observational astronomy, which allows us to see
vistas with remarkable clarity that previously were only imagined, renders
neutron stars to nearly ideal probes for a wide range of physical studies,
including the role of strangeness in dense matter.Comment: 15 pages, 6 figures, Presented at the 5th International Conference on
Strangeness in Quark Matter (Strangeness 2000), Berkeley, California, USA,
July 20-25, 200
Are strange stars distinguishable from neutron stars by their cooling behaviour?
The general statement that strange stars cool more rapidly than neutron stars
is investigated in greater detail. It is found that the direct Urca process
could be forbidden not only in neutron stars but also in strange stars. If so,
strange stars would be slowly cooling and their surface temperatures would be
more or less indistinguishable from those of slowly cooling neutron stars. The
case of enhanced cooling is reinvestigated as well. It is found that strange
stars cool significantly more rapidly than neutron stars within the first years after birth. This feature could become particularly interesting if
continued observation of SN 1987A would reveal the temperature of the possibly
existing pulsar at its centre.Comment: 10 pages, 3 ps-figures, to appear in the proceedings of the
International Symposium on ''Strangeness in Quark Matter 1997``, April
14--18, Thera (Santorini), Hella
Interplay between quantum criticality and geometrical frustration in Fe3Mo3N with stella quadrangula lattice
In the eta-carbide-type correlated-electron metal Fe3Mo3N, ferromagnetism is
abruptly induced from a nonmagnetic non-Fermi-liquid ground state either when a
magnetic field (~14 T) applied to it or when it is doped with a slight amount
of impurity (~5% Co). We observed a peak in the paramagnetic neutron scattering
intensity at finite wave vectors, revealing the presence of the
antiferromagnetic (AF) correlation hidden in the magnetic measurements. It
causes a new type of geometrical frustration in the stellla quadrangula lattice
of the Fe sublattice. We propose that the frustrated AF correlation suppresses
the F correlation to its marginal point and is therfore responsible for the
origin of the ferromagnetic (F) quantum critical behavior in pure Fe3Mo3N
Nambu-Jona-Lasinio Model at the Next-to-Leading Order in 1/N
We derived and solved the compositeness condition in the Nambu-Jona-Lasinio
model at the next-to-leading order in 1/N, and obtained the expressions for the
effective coupling constants in terms of the compositeness scale. In the NJL
model with a scalar composite, the next to leading contributions are too large
for N=3. In the induced gauge theory with abelian gauge symmetry, the
correction term is reasonably suppressed, while, in the SU(N_c) gauge theory
with N_f flavors of fermions, the correction is suppressed only for
N_f>11N_c/2, complementarily to asymptotic freedom.Comment: 7 pages, latex, Invited talk presented at International Conference on
Quark Lepton Nuclear Physics, Osaka, Japan, May 1997. To be published in
Proceeding
Limits on excited tau leptons masses from leptonic tau decays
We study the effects induced by excited leptons on the leptonic tau decay at
one loop level. Using a general effective lagrangian approach to describe the
couplings of the excited leptons, we compute their contributions to the
leptonic decays and use the current experimental values of the branching ratios
to put limits on the mass of excited states and the substructure scale.Comment: 10 pages, 6 figures, to be published in Phys. Rev.
Naturalness Bounds on Dipole Moments from New Physics
Assuming naturalness that the quantum corrections to the mass should not
exceed the order of the observed mass, we derive and apply model-independent
bounds on the anomalous magnetic moments and electric dipole moments of leptons
and quarks due to new physics.Comment: 4 pages, 2 figure
Strange Star Heating Events as a Model for Giant Flares of Soft Gamma-ray Repeaters
Two giant flares were observed on 5 March 1979 and 27 August 1998 from the
soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The
striking similarity between these remarkable bursts strongly implies a common
nature. We show that the light curves of the giant bursts may be easily
explained in the model where the burst radiation is produced by the bare quark
surface of a strange star heated, for example, by impact of a massive
comet-like object.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Letter
Photon and Z induced heavy charged lepton pair production at a hadron supercollider
We investigate the pair production of charged heavy leptons via
photon-induced processes at the proposed CERN Large Hadron Collider (LHC).
Using effective photon and Z approximations, rates are given for
production due to fusion and fusion for the cases of
inelastic, elastic and semi-elastic collisions. These are compared with
the corresponding rates for production via the gluon fusion and Drell-Yan
mechanisms. Various and differential luminosities
for collisions are also presented.Comment: 22 pages, RevTex 3.0, 6 uuencoded and compressed postscript figures
included. Reference to one paper changed from the original preprint number to
the published version. Everything else unchange
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