1,720,992 research outputs found
Asymptotic safety in einstein gravity and scalar-fermion matter
Full text linkWithin the functional renormalization group approach we study the effective quantum field theory of Einstein gravity and one self-interacting scalar coupled to Nf Dirac fermions. We include in our analysis the matter anomalous dimensions induced by all the interactions and analyze the highly nonlinear beta functions determining the renormalization flow. We find the existence of a nontrivial fixed point structure both for the gravity and the matter sector, besides the usual Gaussian matter one. This suggests that asymptotic safety could be realized in the gravitational sector and in the standard model. Nontriviality in the Higgs sector might involve gravitational interactions. © 2010 The American Physical Society
Search of scaling solutions in scalar–tensor gravity
Full text linkWe write new functional renormalization group equations for a scalar nonminimally coupled to gravity. Thanks to the choice of the parametrization and of the gauge fixing they are simpler than older equations and avoid some of the difficulties that were previously present. In three dimensions these equations admit, at least for sufficiently small fields, a solution that may be interpreted as a gravitationally dressed Wilson-Fisher fixed point. We also find for any dimension d>2 two analytic scaling solutions which we study for d=3 and d=4. One of them corresponds to the fixed point of the Einstein-Hilbert truncation, the others involve a nonvanishing minimal coupling
Are there scaling solutions in the O(N)-models for large N in d > 4?
No full textThere have been some speculations about the existence of critical unitary O(N)-invariant scalar field theories in dimensions 4 < d < 6 and for large N. Using the functional renormalization group equation, we show that in the lowest order of the derivative expansion and assuming that the anomalous dimension vanishes for large N, the corresponding critical potentials are either unbounded from below or singular for some finite value of the field
Flow equation for f(R) gravity and some of its exact solutions
No full textWe write a Renormalization Group (RG) equation for the function f in a theory of gravity in the f(R) truncation. Our equation differs from previous ones due to the exponential parametrization of the quantum fluctuations and to the choice of gauge. The cutoff procedure depends on three free parameters, and we find that there exist discrete special choices of parameters for which the flow equation has fixed points where f=f_0+f_1 R+f_2 R^2. For other values of the parameters the solution seems to be continuously deformed
Renormalization group equation and scaling solutions for () gravity in exponential parametrization
Full text linkWe employ the exponential parametrization of the metric and a “physical” gauge fixing procedure to write a functional flow equation for the gravitational effective average action in an f(R) truncation. The background metric is a four-sphere and the coarse-graining procedure contains three free parameters. We look for scaling solutions, i.e. non-Gaussian fixed points for the function f. For a discrete set of values of the parameters, we find simple global solutions of quadratic polynomial form. For other values, global solutions can be found numerically. Such solutions can be extended in certain regions of parameter space and have two relevant directions. We discuss the merits and the shortcomings of this procedure. © 2016, The Author(s)
Critical models with N≤4 scalars in d=4-ε
Full text linkWe adopt a combination of analytical and numerical methods to study the renormalization group flow of the most general field theory with quartic interaction in d=4−ε with N=3 and N=4 scalars. For N=3, we find that it admits only three nondecomposable critical points: the Wilson-Fisher with O(3) symmetry, the cubic with H3=(Z2)3⋊S3 symmetry, and the biconical with O(2)×Z2. For N=4, our analysis reveals the existence of new nontrivial solutions with discrete symmetries and with up to three distinct field anomalous dimensions
Critical models with N≤4 scalars in d=4-ε
Full text linkWe adopt a combination of analytical and numerical methods to study the renormalization group flow of the most general field theory with quartic interaction in d=4-ε with N=3 and N=4 scalars. For N=3, we find that it admits only three nondecomposable critical points: The Wilson-Fisher with O(3) symmetry, the cubic with H3=(Z2)3â ŠS3 symmetry, and the biconical with O(2)×Z2. For N=4, our analysis reveals the existence of new nontrivial solutions with discrete symmetries and with up to three distinct field anomalous dimensions
Symmetry and universality of multifield interactions in 6−ε dimensions
No full textWe outline a general strategy developed for the analysis of critical models, which we apply to obtain a heuristic classification of all universality classes with up to three field-theoretical scalar order parameters in d=6−ε dimensions. As expected by the paradigm of universality, each class is uniquely characterized by its symmetry group and by a set of its scaling properties, neither of which are built-in by the formalism but instead emerge nontrivially as outputs of our computations. For three fields, we find several solutions mostly with discrete symmetries. These are nontrivial conformal field theory candidates in less than six dimensions, one of which is a new perturbatively unitary critical model
Symmetry and universality of multifield interactions in 6-ε dimensions
Full text linkWe outline a general strategy developed for the analysis of critical models, which we apply to obtain a heuristic classification of all universality classes with up to three field-theoretical scalar order parameters in d=6-ε dimensions. As expected by the paradigm of universality, each class is uniquely characterized by its symmetry group and by a set of its scaling properties, neither of which are built-in by the formalism but instead emerge nontrivially as outputs of our computations. For three fields, we find several solutions mostly with discrete symmetries. These are nontrivial conformal field theory candidates in less than six dimensions, one of which is a new perturbatively unitary critical model
Gravitational collapse of a radiating shell
No full textWe study the collapse of a self-gravitating and radiating shell of bosonic matter. The matter constituting the shell is quantized and the construction is viewed as a semiclassical model of possible black hole formation. It is shown that the shell internal degrees of freedom are excited by the quantum nonadiabaticity of the collapse and, consequently, on coupling them to a massless scalar field, the collapsing matter emits a burst of coherent (thermal) radiation. The back reaction on the trajectory is also estimated. ©2001 The American Physical Society
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