192 research outputs found
Two Loop Renormalization of Massive (p,q) Supersymmetric Sigma Models
We calculate the beta-functions of the general massive (p,q) supersymmetric
sigma model to two loop order using (1,0) superfields. The conditions for
finiteness are discussed in relation to (p,q) supersymmetry. We also calculate
the effective potential using component fields to one loop order and consider
the possibility of perturbative breaking of supersymmetry. The effect of one
loop finite local counter terms and the ultra-violet behaviour of the off-shell
(p,q) models to all orders in perturbation theory are also addressed.Comment: 43 pages phyzzx with 5 figure
Heterotic non-linear sigma models with anti-de Sitter target spaces
We calculate the beta function of non-linear sigma models with S^{D+1} and
AdS_{D+1} target spaces in a 1/D expansion up to order 1/D^2 and to all orders
in \alpha'. This beta function encodes partial information about the spacetime
effective action for the heterotic string to all orders in \alpha'. We argue
that a zero of the beta function, corresponding to a worldsheet CFT with
AdS_{D+1} target space, arises from competition between the one-loop and
higher-loop terms, similarly to the bosonic and supersymmetric cases studied
previously in hep-th/0512355. Various critical exponents of the non-linear
sigma model are calculated, and checks of the calculation are presented.Comment: 36 pages, 7 figure
Ultraviolet properties of noncommutative non-linear sigma-models in two dimensions
We discuss the ultra-violet properties of bosonic and supersymmetric
noncommutative non-linear sigma-models in two dimensions, both with and without
a Wess-Zumino-Witten term.Comment: 10 pages, including 1 figure. Plain TeX. Uses Harvmac and epsf. Minor
revisions and additional reference. Version to be published in Phys. Lett.
Exact Bosonic and Supersymmetric String Black Hole Solutions
We show that Witten's two-dimensional string black hole metric is exactly
conformally invariant in the supersymmetric case. We also demonstrate that this
metric, together with a recently proposed exact metric for the bosonic case,
are respectively consistent with the supersymmetric and bosonic -model
conformal invariance conditions up to four-loop order.Comment: 14
On Anomaly-free Supergravity as an Effective String Theory
The equations of motion of anomaly-free supergravity are shown to fulfil (to
all orders in ) a differential condition corresponding to the one
relating the Weyl anomaly coefficients for a non-linear sigma model
representing a (heterotic) string propagating in a non-trivial background. This
supports the possibility that anomaly-free supergravity could provide the
complete massless effective theory for the heterotic string.Comment: 7 pages, Latex, CERN-TH.6686/9
The Rat Lux Actuating Search Task (LAST) and Effects of Sleep Deprivation on Task Reversal Performance
The article of record as published may be found at�https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4124170Sleep deprivation (SD) causes significant deficits in multiple aspects of cognition, including sustained attention and working memory. Investigating the neural processes underpinning these cognitive losses has proven challenging due to the confounds of current animal tasks; many employ appetitive or aversive stimuli to motivate behavior, while others lack task complexity that translates to human studies of executive function. We established the Lux Actuating Search Task (LAST) to circumvent these issues. The LAST is performed in a circular, open-field arena that requires rats to find an unmarked, quasi-randomly positioned target. Constant low-level floor vibrations motivate ambulation, while light intensity (determined by the rodent's proximity to the target destination) provides continuous visual feedback. The task has two paradigms that differ based on the relationship between the light intensity and target proximity: the Low Lux Target (LLT) paradigm and the High Lux Target paradigm (HLT). In this study, on days 1 to 6, the rats completed nine trials per day on one of the two paradigms. On day 7, the rats were either sleep deprived by gentle handling or were left undisturbed before undertaking the opposite (reversal) paradigm on days 7 to 9. Our results showed that SD significantly impeded the ability of Long Evans rats to learn the reversal paradigm, as indicated by increased times to target and increased failure percentages compared to rats whose sleep was undisturbed. Rats also showed reduced learning with the HLT paradigm, as the initial task or as the reversal task, likely due to the rodents' photophobia limiting their motivation to navigate toward a bright light, which is required to succeed
O(d,d) invariance at two and three loops
We show that in a two-dimensional sigma-model whose fields only depend on one
target space co-ordinate, the O(d,d) invariance of the conformal invariance
conditions observed at one loop is preserved at two loops (in the general case
with torsion) and at three loops (in the case without torsion).Comment: 21 pages. Plain Tex. Uses Harvmac ("b" option). Revised Version with
references added and minor errors correcte
Finiteness and anomalies in (4,0) supersymmetric sigma models
Power-counting arguments based on extended superfields have been used to
argue that two-dimensional supersymmetric sigma models with (4,0) supersymmetry
are finite. This result is confirmed up to three loop order in pertubation
theory by an explicit calculation using (1,0) superfields. In particular, it is
shown that the finite counterterms which must be introduced into the theory in
order to maintain (4,0) supersymmetry are precisely the terms that are required
to establish ultra-violet finiteness.Comment: 19 page
Heterotic string solutions and coset conformal field theories
We discuss solutions of the heterotic string theory which are analogous to
bosonic and superstring backgrounds related to coset conformal field theories.
A class of exact `left-right symmetric' solutions is obtained by supplementing
the metric, antisymmetric tensor and dilaton of the superstring solutions by
the gauge field background equal to the generalised Lorentz connection with
torsion. As in the superstring case, these backgrounds are \a'-independent,
i.e. have a `semiclassical' form. The corresponding heterotic string sigma
model is obtained from the combination of the (1,0) supersymmetric gauged WZNW
action with the action of internal fermions coupled to the target space gauge
field. The pure (1,0) supersymmetric gauged WZNW theory is anomalous and does
not describe a consistent heterotic string solution. We also find (to the order
) a two-dimensional perturbative heterotic string solution with the
trivial gauge field background. To the leading order in it coincides
with the known bosonic or superstring solutions. This solution
does not correspond to a `heterotic' combination of the left superstring and
right bosonic -operators at the conformal field theory level. Some duality
properties of the heterotic string solutions are studied.Comment: 28 pages, harvmac (b), CERN-TH.6872/93, RI-150-9
A class of finite two - dimensional sigma models and string vacua
We consider a two - dimensional Minkowski signature sigma model with a
- dimensional target space metric having a null Killing vector. It is shown
that the model is finite to all orders of the loop expansion if the dependence
of the ``transverse" part of the metric \ggij (u,x) on the light cone
coordinate is subject to the standard renormalization group equation of the
- dimensional sigma model, {d\ggij\over du} = \gb_{ij} =R_{ij} + ... .
In particular, we discuss the `one - coupling' case when \ggij(u,x) is a
metric of an - dimensional symmetric space \gij(x) multiplied by a
function . The theory is finite if is equal to the ``running"
coupling of the symmetric space sigma model (with playing the role of the
RG ``time"). For example, the geometry of space - time with \gij being the
metric of the - sphere is determined by the form of the \gb - function of
the model. The ``asymptotic freedom" limit of large corresponds to
the weak coupling limit of small - dimensional curvature. We prove that
there exists a dilaton field which together with the - dimensional metric
solves the sigma model Weyl invariance conditions. The resulting backgrounds
thus represent new tree level string vacua. We also remark on possible
connections with some quantum gravity models.Comment: 15 pages [Complete revision. The main statement of the previous
version is generalised to the case of an arbitrary ``transverse" metric
satisfying sigma model renormalization group equation.
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