15,652 research outputs found
Fractional charge excitations in fermionic ladders
The system of interacting spinless fermions hopping on a two-leg ladder in
the presence of an external magnetic field is shown to possess a long range
order: the bond density wave or the staggered flux phase. In both cases the
elementary excitations are kinks and carry one half the charge of an
electron.Comment: 4 pages, 3 figure
Unbinding of giant vortices in states of competing order
Funding: EPSRC (UK) via Grants No. EP/I031014/1 and No. EP/H049584/1.We consider a two-dimensional system with two order parameters, one with O(2) symmetry and one with O(M), near a point in parameter space where they couple to become a single O(2+M) order. While the O(2) sector supports vortex excitations, these vortices must somehow disappear as the high symmetry point is approached. We develop a variational argument which shows that the size of the vortex cores diverges as 1/root Delta and the Berezinskii-Kosterlitz-Thouless transition temperature of the O(2) order vanishes as 1/1n(1/Delta), where Delta denotes the distance from the high-symmetry point. Our physical picture is confirmed by a renormalization group analysis which gives further logarithmic corrections, and demonstrates full symmetry restoration within the cores.Publisher PDFPeer reviewe
Unkindest cuts: reflections on destruction and resilience in LGBTQ community-based mental health support
This article reflects on the closure of specialist community-based LGBTQ mental health support from the perspective of people who have used or work in such services. The authors discuss the need for community-based specialist support for LGBTQ people who experience mental health problems or work in mental health services
Stability criterion for self-similar solutions with a scalar field and those with a stiff fluid in general relativity
A stability criterion is derived in general relativity for self-similar
solutions with a scalar field and those with a stiff fluid, which is a perfect
fluid with the equation of state . A wide class of self-similar
solutions turn out to be unstable against kink mode perturbation. According to
the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be
a critical solution for the spherical collapse of a stiff fluid if we allow
sufficiently small discontinuity in the density gradient field in the initial
data sets. The self-similar scalar-field solution, which was recently found
numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19}
6359), is also unstable. Both the flat Friedmann universe with a scalar field
and that with a stiff fluid suffer from kink instability at the particle
horizon scale.Comment: 15 pages, accepted for publication in Classical and Quantum Gravity,
typos correcte
Evolution of primordial black holes in Jordan-Brans-Dicke cosmology
We consider the evolution of primordial black holes in a generalyzed
Jordan-Brans-Dicke cosmological model where both the Brans-Dicke scalar field
and its coupling to gravity are dynamical functions determined from the
evolution equations. The evaporation rate for the black holes changes compared
to that in standard cosmology. We show that accretion of radiation can proceed
effectively in the radiation dominated era. The black hole lifetime shortens
for low initial mass, but increases for high initial mass, and is thus
considerably modified compared to the case of standard cosmology. We derive a
cut-off value for the initial black hole mass, below which primordial black
holes evaporate out in the radiation dominated era, and above which they
survive beyond the present era.Comment: 5 pages, Latex; uses MNRAS stylefiles; minor changes; accepted for
publication in MNRA
Strong correlation effects in single-wall carbon nanotubes
We present an overview of strong correlations in single-wall carbon
nanotubes, and an introduction to the techniques used to study them
theoretically. We concentrate on zigzag nanotubes, although universality
dictates that much ofthe theory can also be applied to armchair or chiral
nanotubes. We show how interaction effects lead to exotic low energy properties
and discuss future directions for studies on correlation effects in nanotubes
Evaluation of Mental Effectiveness Training for people with experience of using mental health services
Growth of primordial black holes in a universe containing a massless scalar field
The evolution of primordial black holes in a flat Friedmann universe with a
massless scalar field is investigated in fully general relativistic numerical
relativity. A primordial black hole is expected to form with a scale comparable
to the cosmological apparent horizon, in which case it may go through an
initial phase with significant accretion. However, if it is very close to the
cosmological apparent horizon size, the accretion is suppressed due to general
relativistic effects. In any case, it soon gets smaller than the cosmological
horizon and thereafter it can be approximated as an isolated vacuum solution
with decaying mass accretion. In this situation the dynamical and inhomogeneous
scalar field is typically equivalent to a perfect fluid with a stiff equation
of state . The black hole mass never increases by more than a factor of
two, despite recent claims that primordial black holes might grow substantially
through accreting quintessence. It is found that the gravitational memory
scenario, proposed for primordial black holes in Brans-Dicke and scalar-tensor
theories of gravity, is highly unphysical.Comment: 24 pages, accepted for publication in Physical Review
Repository Software as a Platform for the Registry of Open Access Repositories
We have migrated the ROAR service to a repository software-based platform.
The goal of this project was to reduce the administrative overhead for us and improve the experience for users by enabling them to control and update their own records
Repository Software as a Platform for the Registry of Open Access Repositories
We have migrated the ROAR service to a repository software-based platform.
The goal of this project was to reduce the administrative overhead for us and improve the experience for users by enabling them to control and update their own records
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