1,528 research outputs found
The beta functions of a scalar theory coupled to gravity
We study a scalar field theory coupled to gravity on a flat background, below
Planck's energy. Einstein's theory is treated as an effective field theory.
Within the context of Wilson's renormalization group, we compute gravitational
corrections to the beta functions and the anomalous dimension of the scalar
field, taking into account threshold effects.Comment: 13 pages, plainTe
Effective average action in statistical physics and quantum field theory
An exact renormalization group equation describes the dependence of the free
energy on an infrared cutoff for the quantum or thermal fluctuations. It
interpolates between the microphysical laws and the complex macroscopic
phenomena. We present a simple unified description of critical phenomena for
O(N)-symmetric scalar models in two, three or four dimensions, including
essential scaling for the Kosterlitz-Thouless transition.Comment: 34 pages,5 figures,LaTe
Exact Ward-Takahashi identity for the lattice N=1 Wess-Zumino model
The lattice Wess-Zumino model written in terms of the Ginsparg-Wilson
relation is invariant under a generalized supersymmetry transformation which is
determined by an iterative procedure in the coupling constant. By studying the
associated Ward-Takahashi identity up to order we show that this lattice
supersymmetry automatically leads to restoration of continuum supersymmetry
without fine tuning. In particular, the scalar and fermion renormalization wave
functions coincide.Comment: 6 pages, 5 figures, Talk given at QG05, Cala Gonone, Sardinia, Italy.
12-16 September 200
Multivalued Fields on the Complex Plane and Conformal Field Theories
In this paper a class of conformal field theories with nonabelian and
discrete group of symmetry is investigated. These theories are realized in
terms of free scalar fields starting from the simple systems and scalar
fields on algebraic curves. The Knizhnik-Zamolodchikov equations for the
conformal blocks can be explicitly solved. Besides of the fact that one obtains
in this way an entire class of theories in which the operators obey a
nonstandard statistics, these systems are interesting in exploring the
connection between statistics and curved space-times, at least in the two
dimensional case.Comment: (revised version), 30 pages + one figure (not included), (requires
harvmac.tex), LMU-TPW 92-1
Fructose-1,6-bisphosphate couples glycolytic flux to activation of Ras
Yeast and cancer cells share the unusual characteristic of favoring fermentation of sugar over respiration. We now reveal an evolutionary conserved mechanism linking fermentation to activation of Ras, a major regulator of cell proliferation in yeast and mammalian cells, and prime proto-oncogene product. A yeast mutant (tps1Î) with overactive influx of glucose into glycolysis and hyperaccumulation of Fru1,6bisP, shows hyperactivation of Ras, which causes its glucose growth defect by triggering apoptosis. Fru1,6bisP is a potent activator of Ras in permeabilized yeast cells, likely acting through Cdc25. As in yeast, glucose triggers activation of Ras and its downstream targets MEK and ERK in mammalian cells. Biolayer interferometry measurements show that physiological concentrations of Fru1,6bisP stimulate dissociation of the pure Sos1/H-Ras complex. Thermal shift assay confirms direct binding to Sos1, the mammalian ortholog of Cdc25. Our results suggest that the Warburg effect creates a vicious cycle through Fru1,6bisP activation of Ras, by which enhanced fermentation stimulates oncogenic potency. © 2017 The Author(s)
Monte Carlo simulations and field transformation: the scalar case
We describe a new method in lattice field theory to compute observables at
various values of the parameters lambda_i in the action S[phi,lambda_i].
Firstly one performs a single simulation of a ``reference action'' S[phi^r,
lambda_i^r] with fixed lambda_i^r. Then the phi^r-configurations are
transformed into those of a field phi distributed according to S[phi,lambda_i],
apart from a ``remainder action'' which enters as a \break weight. In this way
we measure the observables at values of lambda_i different from lambda_i^r. We
study the performance of the algorithm in the case of the simplest
renormalizable model, namely the phi^4 scalar theory on a four dimensional
lattice and compare the method with the ``histogram'' technique of which it is
a generalization.Comment: Latex, 23 pgs, 8 eps-figures include
Renormalization of the Hamiltonian and a geometric interpretation of asymptotic freedom
Using a novel approach to renormalization in the Hamiltonian formalism, we
study the connection between asymptotic freedom and the renormalization group
flow of the configuration space metric. It is argued that in asymptotically
free theories the effective distance between configuration decreases as high
momentum modes are integrated out.Comment: 22 pages, LaTeX, no figures; final version accepted in Phys.Rev.D;
added reference and appendix with comment on solution of eq. (9) in the tex
Running coupling in Yang-Mills theory - a flow equation study -
The effective average action of Yang-Mills theory is analyzed in the
framework of exact renormalization group flow equations. Employing the
background-field method and using a cutoff that is adjusted to the spectral
flow, the running of the gauge coupling is obtained on all scales. In four
dimensions and for the gauge groups SU(2) and SU(3), the coupling approaches a
fixed point in the infrared.Comment: 35 pages, 3 figures, v2: References added, minor improvements,
version to appear in PR
Nonperturbative Evolution Equation for Quantum Gravity
A scale--dependent effective action for gravity is introduced and an exact
nonperturbative evolution equation is derived which governs its renormalization
group flow. It is invariant under general coordinate transformations and
satisfies modified BRS Ward--Identities. The evolution equation is solved for a
simple truncation of the space of actions. In 2+epsilon dimensions,
nonperturbative corrections to the beta--function of Newton's constant are
derived and its dependence on the cosmological constant is investigated. In 4
dimensions, Einstein gravity is found to be ``antiscreening'', i.e., Newton's
constant increases at large distances.Comment: 35 pages, late
Exact and Truncated Dynamics in Nonequilibrium Field Theory
Nonperturbative dynamics of quantum fields out of equilibrium is often
described by the time evolution of a hierarchy of correlation functions, using
approximation methods such as Hartree, large N, and nPI-effective action
techniques. These truncation schemes can be implemented equally well in a
classical statistical system, where results can be tested by comparison with
the complete nonlinear evolution obtained by numerical methods. For a 1+1
dimensional scalar field we find that the early-time behaviour is reproduced
qualitatively by the Hartree dynamics. The inclusion of direct scattering
improves this to the quantitative level. We show that the emergence of
nonthermal temperature profiles at intermediate times can be understood in
terms of the fixed points of the evolution equations in the Hartree
approximation. The form of the profile depends explicitly on the initial
ensemble. While the truncated evolution equations do not seem to be able to get
away from the fixed point, the full nonlinear evolution shows thermalization
with a (surprisingly) slow relaxation.Comment: 30 pages with 12 eps figures, minor changes; to appear in Phys.Rev.
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