scholarly journals Leading order QCD shear viscosity from the three-particle irreducible effective action

2009 ◽  
Vol 80 (8) ◽  
Author(s):  
M. E. Carrington ◽  
E. Kovalchuk
Keyword(s):  
Shear Viscosity ◽  
Effective Action ◽  
Leading Order

scholarly journals Forward Higgs production within high energy factorization in the heavy quark limit at next-to-leading order accuracy

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
M. Hentschinski ◽  
K. Kutak ◽  
A. van Hameren
Keyword(s):  
Effective Action ◽  
High Energy ◽  
Higgs Production ◽  
Explicit Calculation ◽  
Leading Order ◽  
Forward Region ◽  
Transverse Momentum Dependent ◽  
Heavy Quark Limit ◽  
Proper Definition ◽  
Definition Of

AbstractWe use Lipatov’s high energy effective action to determine the next-to-leading order corrections to Higgs production in the forward region within high energy factorization making use of the infinite top mass limit. Our result is based on an explicit calculation of real corrections combined with virtual corrections determined earlier by Nefedov. As a new element we provide a proper definition of the desired next-to-leading order coefficient within the high energy effective action framework, extending a previously proposed prescription. We further propose a subtraction mechanism to achieve for this coefficient a stable cancellation of real and virtual infra-red singularities in the presence of external off-shell legs. Apart from its relevance for direct phenomenological studies, such as high energy resummation of Higgs $$+$$ + jet configurations, our result will be further of use for the study of transverse momentum dependent factorization in the high energy limit.

scholarly journals On the Superstrings-Induced Four-Dimensional Gravity and Its Applications to Cosmology

2008 ◽  
Vol 2008 ◽  
pp. 1-27 ◽  
Author(s):  
Masao Iihoshi ◽  
Sergei V. Ketov
Keyword(s):  
Effective Action ◽  
Leading Order ◽  
De Sitter ◽  
Frw Cosmology ◽  
Spacetime Singularity ◽  
Spacetime Curvature ◽  
The Status ◽  
Dimensional Gravity ◽  
Definition Of ◽  
M Theory

We review the status of the fourth-order (quartic in the spacetime curvature) terms induced by superstrings/M-theory (compactified on a warped torus) in the leading order with respect to the Regge slope parameter, and study their (nonperturbative) impact on the evolution of the Hubble scale in the context of the four-dimensional FRW cosmology. After taking into account the quantum ambiguities in the definition of the off-shell superstring effective action, we propose the generalized Friedmann equations, find the existence of their (de Sitter) exact inflationary solutions without a spacetime singularity, and constrain the ambiguities by demanding stability and the scale factor duality invariance of our solutions. The most naive (Bel-Robinson tensor squared) quartic terms are ruled out, thus giving the evidence for the necessity of extra quartic (Ricci tensor-dependent) terms in the off-shell gravitational effective action for superstrings. Our methods are generalizable to the higher orders in the spacetime curvature.

scholarly journals Low-Shear QCD Plasma from Perturbation Theory

Proceedings ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 7 ◽  
Author(s):  
Greg Jackson ◽  
André Peshier
Keyword(s):  
Perturbation Theory ◽  
Shear Viscosity ◽  
Entropy Density ◽  
Leading Order ◽  
Running Coupling ◽  
Low Shear

We argue that the inferred ratio of shear viscosity to entropy density of the quark-gluonplasma, h/s < 0.5 near the deconfinement temperature Tc, can be understood from perturbative QCD.To rebut opposite views, we first show that the existing leading order result should not be expandedin logarithms. After then settling the question of scale for the running coupling, we establish atemperature dependence of h/s which agrees well with constraints from hydrodynamics.

scholarly journals Next-to-leading order corrections to the gluon-induced forward jet vertex from the high energy effective action

2013 ◽  
Vol 87 (7) ◽  
Author(s):  
G. Chachamis ◽  
M. Hentschinski ◽  
J. D. Madrigal Martínez ◽  
A. Sabio Vera
Keyword(s):  
Effective Action ◽  
High Energy ◽  
Leading Order

scholarly journals Surface terms in effective action of O-plane at order $$\alpha '^2$$

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Yasser Akou ◽  
Mohammad R. Garousi
Keyword(s):  
String Theory ◽  
Effective Action ◽  
Type Ii ◽  
Leading Order ◽  
Open Manifold ◽  
Gauge Transformations ◽  
Duality Transformations ◽  
Boundary Terms ◽  
String Dualities ◽  
Superstring Theories

AbstractThe effective action of string theory has both bulk and boundary terms if the spacetime is an open manifold. Recently, the known classical effective action of string theory at the leading order of $$\alpha '$$ α ′ and its corresponding boundary action have been reproduced by constraining the effective actions to be invariant under gauge transformations and under string duality transformations. In this paper, we use this idea to find the classical effective action of the O-plane and its corresponding boundary terms in type II superstring theories at order $$\alpha '^2$$ α ′ 2 and for NS–NS couplings. We find that these constraints fix the bulk action and its corresponding boundary terms up to one overall factor. They also produce three multiplets in the boundary action that their coefficients are independent of the bulk couplings under the string dualities.

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