Double logs of perturbative QCD for parton jets and soft hadron spectra

The influence of coherence in a soft parton bremsstrahlung on hadron spectra in jets is discussed. We present a simple functional method for calculation of different inclusive parton distributions in the “plateau” region. Inclusive parton cross sections, spectra, multiplicities, energy and angular correlations, etc. are derived in the Double Logarithmic approximation.     

Taming perturbative divergences in asymptotically safe gravity

We use functional renormalization group methods to study gravity minimally coupled to a free scalar field. This setup provides the prototype of a gravitational theory which is perturbatively non-renormalizable at one-loop level, but may possess a non-trivial renormalization group fixed point controlling its UV behavior. We show that such a fixed point indeed exists within the truncations considered, lending strong support to the conjectured asymptotic safety of the theory. In particular, we demonstrate that the counterterms responsible for its perturbative non-renormalizability have no qualitative effect on this feature.     

Finite field-dependent symmetries in perturbative quantum gravity

In this paper we discuss the absolutely anticommuting nilpotent symmetries for perturbative quantum gravity in general curved spacetime in linear and non-linear gauges. Further, we analyze the finite field-dependent BRST (FFBRST) transformation for perturbative quantum gravity in general curved spacetime. The FFBRST transformation changes the gauge-fixing and ghost parts of the perturbative quantum gravity within functional integration. However, the operation of such symmetry transformation on the generating functional of perturbative quantum gravity does not affect the theory on physical ground. The FFBRST transformation with appropriate choices of finite BRST parameter connects non-linear Curci–Ferrari and Landau gauges of perturbative quantum gravity. The validity of the results is also established at quantum level using Batalin–Vilkovisky (BV) formulation.     

A perturbative approach to chiral induced two-dimensional gravity

In the framework of the covariant approach, based on perturbation theory, two-dimensional chiral induced quantum gravity is analyzed. The quantum equivalence with the local version of two-dimensional induced quantum gravity is established.Lenin Komsemol Tomsk State Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 102–105, December, 1992.     

Unreasonable postulate in the perturbative approach to quantum gravity

The conventional perturbative approach to quantum gravity is based on the expansion in powers of k, wherek denotes the Einstein gravitational constant. The introduction of a square root is due to the unreasonable postulate that thek0 limit of the gravitational field is ac-number. It is more natural that it is aq-number, which can be determined explicitly by the theory, and then the expansion becomes that in powers ofk but not of k. Thus the nonrenormalizability of Einstein gravity should be completely reconsidered in the light of the new expansion.     

Generalised BRST symmetry and gaugeon formalism for perturbative quantum gravity: Novel observation

In this paper the novel features of Yokoyama gaugeon formalism are stressed out for the theory of perturbative quantum gravity in the Einstein curved spacetime. The quantum gauge transformations for the theory of perturbative gravity are demonstrated in the framework of gaugeon formalism. These quantum gauge transformations lead to renormalised gauge parameter. Further, we analyse the BRST symmetric gaugeon formalism which embeds more acceptable Kugo–Ojima subsidiary condition. Further, the BRST symmetry is made finite and field-dependent. Remarkably, the Jacobian of path integral under finite and field-dependent BRST symmetry amounts to the exact gaugeon action in the effective theory of perturbative quantum gravity.     

Double scattering on the nucleus in the perturbative QCD

In the hard pomeron model consequences are studied which follow from the recently obtained form of the diffractive amplitude for the double scattering on the nucleus and the related EMC effect at small x. It is shown that at large Q²Q^2 to the double scattering contribution to the latter falls as Q^-0.6338Q^{-0.6338} and in all probability dominates the total effect.     

The structure of perturbative quantum gravity on a de Sitter background

Classical gravitation on de Sitter space suffers from a linearization instability. One consequence is that the causal response to a spatially localized distribution of positive energy cannot be globally regular. We use this fact to show that no causal Green's function can give the correct linearized response to certain bilocalized distributions, even though these distributions obey the constraints of linearization stability. We avoid the problem by working on the open submanifold spanned by conformal coordinates. The retarded Green's function is first computed in a simple gauge, then the rest of the propagator is inferred by analyticity — up to the usual ambiguity about real, analytic and homogeneous terms. We show that the latter can be chosen so as to give a propagator which does not grow in any direction. The ghost propagator is also given and the interaction vertices are worked out.     

No black-hole theorem in three-dimensional gravity

A common property of known black-hole solutions in (2+1)-dimensional gravity is that they require a negative cosmological constant. To explain this, it is shown in this Letter that a (2+1)-dimensional gravity theory which satisfies the dominant energy condition forbids the existence of a black hole.     

The Birkhoff theorem in multidimensional gravity

The validity conditions for the extended Birkhoff theorem in multidimensional gravity withn internal spaces are formulated, with no restriction on space-time dimensionality and signature. Examples of matter sources and geometries for which the theorem is valid are given. Further generalization of the theorem is discussed.     

Fundamental constants,entropic gravity and nonextensive equipartition theorem

By using Verlinde’s formalism, we propose that the positive numerical factor, in which Klinkhamer states that it is necessary to define the fundamental length, can be associated to the parameter q$q$ of Tsallis’ nonextensive statistical mechanics.     

A no-hair theorem for spherically symmetric black holes in $$R^2$$ gravity

In a recent paper Cañate (Class Quantum Grav 35:025018, 2018) proved a no hair theorem to static and spherically symmetric or stationary axisymmetric black holes in general f(R) gravity. The theorem applies for isolated asymptotically flat or asymptotically de Sitter black holes and also in the case when vacuum is replaced by a minimally coupled source having a traceless energy momentum tensor. This theorem excludes the case of pure quadratic gravity, \(f(R) = R^2\). In this paper we use the scalar tensor representation of general f(R) theory to show that there are no hairy black hole in pure \(R^2\) gravity. The result is limited to spherically symmetric black holes but does not assume asymptotic flatness or de-Sitter asymptotics as in most of the no-hair theorems encountered in the literature. We include an example of a static and spherically symmetric black hole in \(R^2\) gravity with a conformally coupled scalar field having a Higgs-type quartic potential.     

Hulthen势的微扰计算(英文)

运用一种选择性的近似方法解Hulthen势的薛定谔方程,对于各种本征态的束缚态能量计算到二级近似,并且相应的波函数计算到一级近似.这种微扰方法也可应用于原子物理的其它领域.