205 research outputs found
Kink interactions in
There are classes of kink solutions in . We show how
interactions between various kinks depend on the classes of individual kinks as
well as on their orientations with respect to each other in the internal space.
In particular, we find that the attractive or repulsive nature of the
interaction depends on the trace of the product of charges of the two kinks. We
calculate the interaction potential for all combinations of kinks and antikinks
in and study their collisions. The outcome of kink-antikink
collisions, as expected from previous studies, is sensitive to their initial
relative velocity. We find that heavier kinks tend to break up into lighter
ones, while interactions between the lightest kinks and antikinks in this model
can be repulsive as well as attractive.Comment: 11 pages, 9 figures. Two insignificant sign errors corrected in the
revised versio
The effects of delayed auditory and visual feedback on speech production
Monitoring the sensory consequences of articulatory movements supports speaking. For example, delaying auditory feedback of a speaker's voice disrupts speech production. Also, there is evidence that this disruption may be decreased by immediate visual feedback, i.e., seeing one's own articulatory movements. It is, however, unknown whether delayed visual feedback affects speech production in fluent speakers. Here, the effects of delayed auditory and visual feedback on speech fluency (i.e., speech rate and errors), vocal control (i.e., intensity and pitch), and speech rhythm were investigated. Participants received delayed (by 200 ms) or immediate auditory feedback, while repeating sentences. Moreover, they received either no visual feedback, immediate visual feedback, or delayed visual feedback (by 200, 400, and 600 ms). Delayed auditory feedback affected fluency, vocal control, and rhythm. Immediate visual feedback had no effect on any of the speech measures when it was combined with delayed auditory feedback. Delayed visual feedback did, however, affect speech fluency when it was combined with delayed auditory feedback. In sum, the findings show that delayed auditory feedback disrupts fluency, vocal control, and rhythm and that delayed visual feedback can strengthen the disruptive effect of delayed auditory feedback on fluency
Confining strings in SU(N) gauge theories
We calculate the string tensions of -strings in SU() gauge theories in
both 3 and 4 dimensions. In D=3+1, we find that the ratio of the string
tension to the fundamental string tension is consistent, at the level, with both the M(-theory)QCD-inspired conjecture and with
`Casimir scaling'. In D=2+1 we see a definite deviation from the MQCD formula,
as well as a much smaller but still significant deviation from Casimir scaling.
We find that in both D=2+1 and D=3+1 the high temperature spatial -string
tensions also satisfy approximate Casimir scaling. We point out that
approximate Casimir scaling arises naturally if the cross-section of the flux
tube is nearly independent of the flux carried, and that this will occur in an
effective dual superconducting description, if we are in the deep-London limit.
We estimate, numerically, the intrinsic width of -strings in D=2+1 and
indeed find little variation with . In addition to the stable -strings we
investigate some ofthe unstable strings, finding in D=2+1 that they satisfy
(approximate) Casimir scaling. We also investigate the basic assumption that
confining flux tubes are described by an effective string theory at large
distances. We estimate the coefficient of the universal L\"uscher correction
from periodic strings that are longer than 1 fermi, and find in
D=3+1 and in D=2+1. These values are within of the
simple bosonic string values and are inconsistent with other simple effective
string theories.Comment: 57 pages, 11 figures. Errors on fits reduced by altering the analysis
to a standard one. Conclusions unchanged; note addedchanged. Some typos
correcte
Non-perturbative Renormalisation of Domain Wall Fermions: Quark Bilinears
We find the renormalisation coefficients of the quark field and the flavour
non-singlet fermion bilinear operators for the domain wall fermion action, in
the regularisation independent (RI) renormalisation scheme. Our results are
from a quenched simulation, on a 16^3x32 lattice, with beta=6.0 and an extent
in the fifth dimension of 16. We also discuss the expected effects of the
residual chiral symmetry breaking inherent in a domain wall fermion simulation
with a finite fifth dimension, and study the evidence for both explicit and
spontaneous chiral symmetry breaking effects in our numerical results. We find
that the relations between different renormalisation factors predicted by
chiral symmetry are, to a good approximation, satisfied by our results and that
systematic effects due to the (low energy) spontaneous chiral symmetry breaking
and zero-modes can be controlled. Our results are compared against the
perturbative predictions for both their absolute value and renormalisation
scale dependence.Comment: 53 pages, 21 figures, revte
Quenched Lattice QCD with Domain Wall Fermions and the Chiral Limit
Quenched QCD simulations on three volumes, , and
and three couplings, , 5.85 and 6.0 using domain
wall fermions provide a consistent picture of quenched QCD. We demonstrate that
the small induced effects of chiral symmetry breaking inherent in this
formulation can be described by a residual mass (\mres) whose size decreases
as the separation between the domain walls () is increased. However, at
stronger couplings much larger values of are required to achieve a given
physical value of \mres. For and , we find
\mres/m_s=0.033(3), while for , and ,
\mres/m_s=0.074(5), where is the strange quark mass. These values are
significantly smaller than those obtained from a more naive determination in
our earlier studies. Important effects of topological near zero modes which
should afflict an accurate quenched calculation are easily visible in both the
chiral condensate and the pion propagator. These effects can be controlled by
working at an appropriately large volume. A non-linear behavior of in
the limit of small quark mass suggests the presence of additional infrared
subtlety in the quenched approximation. Good scaling is seen both in masses and
in over our entire range, with inverse lattice spacing varying between
1 and 2 GeV.Comment: 91 pages, 34 figure
k-string tensions in SU(N) gauge theories
In the context of four-dimensional SU(N) gauge theories, we study the
spectrum of the confining strings. We compute, for the SU(6) gauge theory
formulated on a lattice, the three independent string tensions sigma_k related
to sources with Z_N charge k=1,2,3, using Monte Carlo simulations. Our results,
whose uncertainty is approximately 2% for k=2 and 4% for k=3, are consistent
with the sine formula sigma_k/sigma = sin(k pi/N) / \sin(pi/N) for the ratio
between sigma_k and the standard string tension sigma, and show deviations from
the Casimir scaling.
The sine formula is known to emerge in supersymmetric SU(N) gauge theories
and in M-theory. We comment on an analogous behavior exhibited by
two-dimensional SU(N)xSU(N) chiral models.Comment: version accepted for publication in Phys Rev D (Rap Comm
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
A Lattice Study of the Nucleon Excited States with Domain Wall Fermions
We present results of our numerical calculation of the mass spectrum for
isospin one-half and spin one-half non-strange baryons, i.e. the ground and
excited states of the nucleon, in quenched lattice QCD. We use a new lattice
discretization scheme for fermions, domain wall fermions, which possess almost
exact chiral symmetry at non-zero lattice spacing. We make a systematic
investigation of the negative-parity spectrum by using two distinct
interpolating operators at on a
lattice. The mass estimates extracted from the two operators are consistent
with each other. The observed large mass splitting between this state,
, and the positive-parity ground state, the nucleon N(939), is well
reproduced by our calculations. We have also calculated the mass of the first
positive-parity excited state and found that it is heavier than the
negative-parity excited state for the quark masses studied.Comment: 46 pages, REVTeX, 11 figures included, revised version accepted for
publication in Phys. Rev.
miR-132/212 knockout mice reveal roles for these miRNAs in regulating cortical synaptic transmission and plasticity
miR-132 and miR-212 are two closely related miRNAs encoded in the same intron of a small non-coding gene, which have been suggested to play roles in both immune and neuronal function. We describe here the generation and initial characterisation of a miR-132/212 double knockout mouse. These mice were viable and fertile with no overt adverse phenotype. Analysis of innate immune responses, including TLR-induced cytokine production and IFNβ induction in response to viral infection of primary fibroblasts did not reveal any phenotype in the knockouts. In contrast, the loss of miR-132 and miR-212, while not overtly affecting neuronal morphology, did affect synaptic function. In both hippocampal and neocortical slices miR-132/212 knockout reduced basal synaptic transmission, without affecting paired-pulse facilitation. Hippocampal long-term potentiation (LTP) induced by tetanic stimulation was not affected by miR-132/212 deletion, whilst theta burst LTP was enhanced. In contrast, neocortical theta burst-induced LTP was inhibited by loss of miR-132/212. Together these results indicate that miR-132 and/or miR-212 play a significant role in synaptic function, possibly by regulating the number of postsynaptic AMPA receptors under basal conditions and during activity-dependent synaptic plasticity
Wnt/β-catenin Signalling Is Active in a Highly Dynamic Pattern during Development of the Mouse Cerebellum
The adult cerebellum is composed of several distinct cell types with well defined developmental origins. However, the molecular mechanisms that govern the generation of these cell types are only partially resolved. Wnt/β-catenin signalling has a wide variety of roles in generation of the central nervous system, though the specific activity of this pathway during cerebellum development is not well understood. Here, we present data that delineate the spatio-temporal specific pattern of Wnt/β-catenin signaling during mouse cerebellum development between E12.5 and P21. Using the BAT-gal Wnt/β-catenin reporter mouse, we found that Wnt/β-catenin activity is present transiently at the embryonic rhombic lip but not at later stages during the expansion of cell populations that arise from there. At late embryonic and early postnatal stages, Wnt/β-catenin activity shifts to the cerebellar ventricular zone and to cells arising from this germinal centre. Subsequently, the expression pattern becomes progressively restricted to Bergmann glial cells, which show expression of the reporter at P21. These results indicate a variety of potential functions for Wnt/β-catenin activity during cerebellum development
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