11,306 research outputs found
Failed "nonaccelerating" models of prokaryote gene regulatory networks
Much current network analysis is predicated on the assumption that important
biological networks will either possess scale free or exponential statistics
which are independent of network size allowing unconstrained network growth
over time. In this paper, we demonstrate that such network growth models are
unable to explain recent comparative genomics results on the growth of
prokaryote regulatory gene networks as a function of gene number. This failure
largely results as prokaryote regulatory gene networks are "accelerating" and
have total link numbers growing faster than linearly with network size and so
can exhibit transitions from stationary to nonstationary statistics and from
random to scale-free to regular statistics at particular critical network
sizes. In the limit, these networks can undergo transitions so marked as to
constrain network sizes to be below some critical value. This is of interest as
the regulatory gene networks of single celled prokaryotes are indeed
characterized by an accelerating quadratic growth with gene count and are size
constrained to be less than about 10,000 genes encoded in DNA sequence of less
than about 10 megabases. We develop two "nonaccelerating" network models of
prokaryote regulatory gene networks in an endeavor to match observation and
demonstrate that these approaches fail to reproduce observed statistics.Comment: Corrected error in biological input parameter: 13 pages, 9 figure
Validating module network learning algorithms using simulated data
In recent years, several authors have used probabilistic graphical models to
learn expression modules and their regulatory programs from gene expression
data. Here, we demonstrate the use of the synthetic data generator SynTReN for
the purpose of testing and comparing module network learning algorithms. We
introduce a software package for learning module networks, called LeMoNe, which
incorporates a novel strategy for learning regulatory programs. Novelties
include the use of a bottom-up Bayesian hierarchical clustering to construct
the regulatory programs, and the use of a conditional entropy measure to assign
regulators to the regulation program nodes. Using SynTReN data, we test the
performance of LeMoNe in a completely controlled situation and assess the
effect of the methodological changes we made with respect to an existing
software package, namely Genomica. Additionally, we assess the effect of
various parameters, such as the size of the data set and the amount of noise,
on the inference performance. Overall, application of Genomica and LeMoNe to
simulated data sets gave comparable results. However, LeMoNe offers some
advantages, one of them being that the learning process is considerably faster
for larger data sets. Additionally, we show that the location of the regulators
in the LeMoNe regulation programs and their conditional entropy may be used to
prioritize regulators for functional validation, and that the combination of
the bottom-up clustering strategy with the conditional entropy-based assignment
of regulators improves the handling of missing or hidden regulators.Comment: 13 pages, 6 figures + 2 pages, 2 figures supplementary informatio
Gaugino Mass without Singlets
In models with dynamical supersymmetry breaking in the hidden sector, the
gaugino masses in the observable sector have been believed to be extremely
suppressed (below 1 keV), unless there is a gauge singlet in the hidden sector
with specific couplings to the observable sector gauge multiplets. We point out
that there is a pure supergravity contribution to gaugino masses at the quantum
level arising from the superconformal anomaly. Our results are valid to all
orders in perturbation theory and are related to the `exact' beta functions for
soft terms. There is also an anomaly contribution to the A terms proportional
to the beta function of the corresponding Yukawa coupling. The gaugino masses
are proportional to the corresponding gauge beta functions, and so do not
satisfy the usual GUT relations.Comment: 25 pages, references added, typos and grammar correcte
Renormalization group flows for gauge theories in axial gauges
Gauge theories in axial gauges are studied using Exact Renormalisation Group flows. We introduce a background field in the infrared regulator, but not in the gauge fixing, in contrast to the usual background field gauge. It is shown how heat-kernel methods can be used to obtain approximate solutions to the flow and the corresponding Ward identities. Expansion schemes are discussed, which are not applicable in covariant gauges. As an application, we derive the one-loop effective action for covariantly constant field strength, and the one-loop beta-function for arbitrary regulator
Renormalization Ambiguities and Conformal Anomaly in Metric-Scalar Backgrounds
We analyze the problem of the existing ambiguities in the conformal anomaly
in theories with external scalar field in curved backgrounds. In particular, we
consider the anomaly of self-interacting massive scalar field theory and of
Yukawa model in the massless conformal limit. In all cases the ambiguities are
related to finite renormalizations of a local non-minimal terms in the
effective action. We point out the generic nature of this phenomenon and
provide a general method to identify the theories where such an ambiguity can
arise.Comment: RevTeX, 10 pages, no figures. Small comment and two references added.
Accepted for publication in Physical Review
Fermionic Glauber Operators and Quark Reggeization
We derive, in the framework of soft-collinear effective field theory (SCET),
a Lagrangian describing the -channel exchange of Glauber quarks in the Regge
limit. The Glauber quarks are not dynamical, but are incorporated through
non-local fermionic potential operators. These operators are power suppressed
in relative to those describing Glauber gluon exchange, but give the
first non-vanishing contributions in the Regge limit to processes such as
and . They therefore represent an
interesting subset of power corrections to study. The structure of the
operators, which describe certain soft and collinear emissions to all orders
through Wilson lines, is derived from the symmetries of the effective theory
combined with constraints from power and mass dimension counting, as well as
through explicit matching calculations. Lightcone singularities in the
fermionic potentials are regulated using a rapidity regulator, whose
corresponding renormalization group evolution gives rise to the Reggeization of
the quark at the amplitude level and the BFKL equation at the cross section
level. We verify this at one-loop, deriving the Regge trajectory of the quark
in the color channel, as well as the leading logarithmic BFKL equation.
Results in the and color channels are obtained by the
simultaneous exchange of a Glauber quark and a Glauber gluon. SCET with quark
and gluon Glauber operators therefore provides a framework to systematically
study the structure of QCD amplitudes in the Regge limit, and derive
constraints on higher order amplitudes.Comment: 31 pages, many figure
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