1,625 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
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
A common misapplication of statistical inference: nuisance control with null-hypothesis significance tests
Experimental research on behavior and cognition frequently rests on stimulus
or subject selection where not all characteristics can be fully controlled,
even when attempting strict matching. For example, when contrasting patients to
controls, variables such as intelligence or socioeconomic status are often
correlated with patient status. Similarly, when presenting word stimuli,
variables such as word frequency are often correlated with primary variables of
interest. One procedure very commonly employed to control for such nuisance
effects is conducting inferential tests on confounding stimulus or subject
characteristics. For example, if word length is not significantly different for
two stimulus sets, they are considered as matched for word length. Such a test
has high error rates and is conceptually misguided. It reflects a common
misunderstanding of statistical tests: interpreting significance not to refer
to inference about a particular population parameter, but about 1. the sample
in question, 2. the practical relevance of a sample difference (so that a
nonsignificant test is taken to indicate evidence for the absence of relevant
differences). We show inferential testing for assessing nuisance effects to be
inappropriate both pragmatically and philosophically, present a survey showing
its high prevalence, and briefly discuss an alternative in the form of
regression including nuisance variables
Some analytic results for two-loop scattering amplitudes
We present analytic results for the finite diagrams contributing to the
two-loop eight-point MHV scattering amplitude of planar N=4 SYM. We use a
recently proposed representation for the integrand of the amplitude in terms of
(momentum) twistors and focus on a restricted kinematics in which the answer
depends only on two independent cross-ratios. The theory of motives can be used
to vastly simplify the results, which can be expressed as simple combinations
of classical polylogarithms.Comment: 18 page
Scattering into the fifth dimension of N=4 super Yang-Mills
We study an alternative to dimensional regularisation of planar scattering
amplitudes in N=4 super Yang-Mills theory by going to the Coulomb phase of the
theory. The infrared divergences are regulated by masses obtained from a Higgs
mechanism, allowing us to work in four dimensions. The corresponding string
theory set-up suggests that the amplitudes have an exact dual conformal
symmetry. The latter acts on the kinematical variables of the amplitudes as
well as on the Higgs masses in an effectively five dimensional space. We
confirm this expectation by an explicit calculation in the gauge theory. A
consequence of this exact dual conformal symmetry is a significantly reduced
set of scalar basis integrals that are allowed to appear in an amplitude. For
example, triangle sub-graphs are ruled out. We argue that the study of
exponentiation of amplitudes is simpler in the Higgsed theory because
evanescent terms in the mass regulator can be consistently dropped. We
illustrate this by showing the exponentiation of a four-point amplitude to two
loops. Finally, we also analytically compute the small mass expansion of a
two-loop master integral with an internal mass.Comment: 35 pages, many figures. v2: typos and references fixed. v3: minor
changes, version to be published in JHE
Large spin systematics in CFT
20 pages; v2: version published in JHEPUsing conformal field theory (CFT) arguments we derive an infinite number of constraints on the large spin expansion of the anomalous dimensions and structure constants of higher spin operators. These arguments rely only on analiticity, unitarity, crossing-symmetry and the structure of the conformal partial wave expansion. We obtain results for both, perturbative CFT to all order in the perturbation parameter, as well as non-perturbatively. For the case of conformal gauge theories this provides a proof of the reciprocity principle to all orders in perturbation theory and provides a new "reciprocity" principle for structure constants. We argue that these results extend also to non-conformal theories.Peer reviewe
A note on string solutions in AdS_3
We systematically search for classical open string solutions in AdS_3 within
the general class expressed by elliptic functions (i.e., the genus-one
finite-gap solutions). By explicitly solving the reality and Virasoro
conditions, we give a classification of the allowed solutions. When the
elliptic modulus degenerates, we find a class of solutions with six null
boundaries, among which two pairs are collinear. By adding the S^1 sector, we
also find four-cusp solutions with null boundaries expressed by the elliptic
functions.Comment: 17 pages, 1 figure; (v2) added 1 figure and discussion on solutions
with 6 null boundaries; (v3) corrected equation numbers; (v4) added comment
Note About Integrability and Gauge Fixing for Bosonic String on AdS(5)xS(5)
This short note is devoted to the study of the integrability of the bosonic
string on AdS(5)xS(5) in the uniform light-cone gauge. We construct Lax
connection for gauge fixed theory and we argue that it is flat.Comment: 17 page
Supersymmetric solutions to Euclidean Romans supergravity
We study Euclidean Romans supergravity in six dimensions with a non-trivial
Abelian R-symmetry gauge field. We show that supersymmetric solutions are in
one-to-one correspondence with solutions to a set of differential constraints
on an SU(2) structure. As an application of our results we (i) show that this
structure reduces at a conformal boundary to the five-dimensional rigid
supersymmetric geometry previously studied by the authors, (ii) find a general
expression for the holographic dual of the VEV of a BPS Wilson loop, matching
an exact field theory computation, (iii) construct holographic duals to
squashed Sasaki-Einstein backgrounds, again matching to a field theory
computation, and (iv) find new analytic solutions.Comment: 31 pages; v2: published version (with reference added
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