18,215 research outputs found
Magnetic collapse of a neutron gas: Can magnetars indeed be formed
A relativistic degenerate neutron gas in equilibrium with a background of
electrons and protons in a magnetic field exerts its pressure anisotropically,
having a smaller value perpendicular than along the magnetic field. For
critical fields the magnetic pressure may produce the vanishing of the
equatorial pressure of the neutron gas. Taking it as a model for neutron stars,
the outcome could be a transverse collapse of the star. This fixes a limit to
the fields to be observable in stable neutron star pulsars as a function of
their density. The final structure left over after the implosion might be a
mixed phase of nucleons and meson condensate, a strange star, or a highly
distorted black hole or black "cigar", but no any magnetar, if viewed as a
super strongly magnetized neutron star. However, we do not exclude the
possibility of a supersotrong magnetic fields arising in supernova explosions
which lead directly to strange stars. In other words, if any magnetars exist,
they cannot be neutron stars.Comment: 15 pages, 3 figures. European Physical Journal C in pres
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
Cohomological finiteness conditions and centralisers in generalisations of Thompson's group V
We consider generalisations of Thompson's group , denoted ,
which also include the groups of Higman, Stein and Brin. We show that, under
some mild hypotheses, is the full automorphism group of a
Cantor-algebra. Under some further minor restrictions, we prove that these
groups are of type and that this implies that also
centralisers of finite subgroups are of type .Comment: 19 pages, 2 figures. Revised version. The original submission has now
been split into two papers. The current submission contains the first one.
The second part is being reworked and will be reposted soon independently.
Lemma 4.8 was incorrect as stated and has since been rectified. The results
of the paper are unchange
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