3,555 research outputs found
How much baseline correction do we need in ERP research? Extended GLM model can replace baseline correction while lifting its limits
Baseline correction plays an important role in past and current
methodological debates in ERP research (e.g. the Tanner v. Maess debate in
Journal of Neuroscience Methods), serving as a potential alternative to strong
highpass filtering. However, the very assumptions that underlie traditional
baseline also undermine it, making it statistically unnecessary and even
undesirable and reducing signal-to-noise ratio. Including the baseline interval
as a predictor in a GLM-based statistical approach allows the data to determine
how much baseline correction is needed, including both full traditional and no
baseline correction as subcases, while reducing the amount of variance in the
residual error term and thus potentially increasing statistical power
Solving CFTs with Weakly Broken Higher Spin Symmetry
The method of large spin perturbation theory allows to analyse conformal
field theories (CFT) by turning the crossing equations into an algebraic
problem. We apply this method to a generic CFT with weakly broken higher spin
(HS) symmetry, to the first non-trivial order in the breaking parameter. We
show that the spectrum of broken currents, for any value of the spin, follows
from crossing symmetry. After discussing a generic model of a single scalar
field, we focus on vector models with global symmetry. We rediscover the
spectrum of several models, including the Wilson-Fisher model around
four dimensions, the large model in and cubic models around six
dimensions, not necessarily unitary. We also discuss models where the
fundamental field is not part of the spectrum. Examples of this are weakly
coupled gauge theories and our method gives an on-shell gauge invariant way to
study them. At first order in the coupling constant we show that again the
spectrum follows from crossing symmetry, to all values of the spin. Our method
provides an alternative to usual perturbation theory without any reference to a
Lagrangian.Comment: 30 pages,v2:typos correcte
In quest of "just" the Standard Model on D-branes at a singularity
In this note we explore the possibility of obtaining gauge bosons and
fermionic spectrum as close as possible to the Standard Model content, by
placing D3-branes at a ZN orbifold-like singularity in the presence of
D7-branes. Indeed, we find that this is plausible provided a sufficiently high
N is allowed for and the singular point is also fixed by an orientifold action.
If extra charged matter is not permitted then the singularity should
necessarily be non-supersymmetric. Correct hypercharge assignments require a
dependence on some Abelian gauge D7-groups. In achieving such a construction we
follow a recent observation made in Ref. [hep-th/0105155] about the possibility
that, the three left handed quarks, would present different U(2) transformation
properties.Comment: 18 pages, 1 table, no figures, v2: typos correcte
Higher-spin correlators
We analyze the properly normalized three-point correlator of two protected
scalar operators and one higher spin twist-two operator in N=4 super
Yang-Mills, in the limit of large spin j. The relevant structure constant can
be extracted from the OPE of the four-point correlator of protected scalar
operators. We show that crossing symmetry of the four point correlator plus a
judicious guess for the perturbative structure of the three-point correlator,
allow to make a prediction for the structure constant at all loops in
perturbation theory, up to terms that remain finite as the spin becomes large.
Furthermore, the expression for the structure constant allows to propose an
expression for the all loops four-point correlator G(u,v), in the limit u,v ->
0. Our predictions are in perfect agreement with the large j expansion of
results available in the literature.Comment: 14 pages,v2:minor changes, refs adde
The superconformal bootstrap for structure constants
We report on non-perturbative bounds for structure constants on N=4 SYM. Such
bounds are obtained by applying the conformal bootstrap recently extended to
superconformal theories. We compare our results with interpolating functions
suitably restricted by the S-duality of the theory. Within numerical errors,
these interpolations support the conjecture that the bounds found in this paper
are saturated at duality invariant values of the coupling. This extends recent
conjectures for the anomalous dimension of leading twist operators.Comment: 14 pages, 4 figure
Conformal Bootstrap With Slightly Broken Higher Spin Symmetry
We consider conformal field theories with slightly broken higher spin
symmetry in arbitrary spacetime dimensions. We analyze the crossing equation in
the double light-cone limit and solve for the anomalous dimensions of higher
spin currents with large spin . The result depends on the
symmetries and the spectrum of the unperturbed conformal field theory. We
reproduce all known results and make further predictions. In particular we make
a prediction for the anomalous dimensions of higher spin currents in the 3d
Ising model.Comment: 41 pages, 2 figures, %\draftmod
Effective Superpotentials via Konishi Anomaly
We use Ward identities derived from the generalized Konishi anomaly in order
to compute effective superpotentials for SU(N), SO(N) and
supersymmetric gauge theories coupled to matter in various representations. In
particular we focus on cubic and quartic tree level superpotentials. With this
technique higher order corrections to the perturbative part of the effective
superpotential can be easily evaluated.Comment: 17 pages, harvma
Loop Corrections to Supergravity on
We consider the four-point correlator of the stress-energy tensor multiplet
in SYM. In the planar limit and at large 't Hooft coupling such
correlator is given by the corresponding holographic correlation function in
IIB supergravity on . We consider subleading corrections in
the number of colours, i.e. order , at large 't Hooft coupling. This
corresponds to loop corrections to the supergravity result. Consistency
conditions, most notably crossing symmetry, constrain the form of such
corrections and lead to a complete determination of the spectrum of leading
twist intermediate operators.Comment: 6 pages, minor changes, added reference
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