We study integrations over light-cone degrees of freedom in the gauge invariant effective action for high energy processes in QCD. We propose a regularization which takes into account the signature of the reggeized gluon. For a test we apply it to the elastic and the production amplitude.
In the framework of the QCD effective action the vertices of gluon emission in interaction of reggeons are studied in the limit of small longitudinal momenta of the emitted gluon. It is found that the vertices drastically simplify in this limit so that the gluon becomes emitted from a single reggeon coupled to the projectile and target via multireggeon vertices. Contribution from this kinematical region is studied for double and 2x2 elementary collisions inside the composite projectile and target.
The breaking of chiral symmetry in holographic light-front QCD is encoded in its longitudinal dynamics with its chiral limit protected by the superconformal algebraic structure which governs its transverse dynamics. The scale in the longitudinal light-front Hamiltonian determines the confinement strength in this direction: It is also responsible for most of the light meson ground state mass consistent with the Gell-Mann-Oakes-Renner constraint. Longitudinal confinement and the breaking of chiral symmetry are found to be different manifestations of the same underlying dynamics as found in 't Ho…
The effects of longitudinal bulk viscous pressure on the heavy quark dynamics have been estimated in a strongly magnetized quark-gluon plasma within the Fokker-Planck approach. The bulk viscous modification to the momentum distribution of bulk degrees of freedom has been obtained in the presence of a magnetic field while incorporating the realistic equation of state of the hot magnetized QCD medium. As the magnetic field breaks the isotropy of the medium, the analysis is done along the directions longitudinal and transverse to the field. The longitudinal bulk viscous contribution is seen to ha…
We present analytical expressions for the 31 five-particle phase-space master integrals in massless QCD as an $ε$-series with coefficients being multiple zeta values of weight up to 12. In addition, we provide computer code for the Monte-Carlo integration in higher dimensions, based on the RAMBO algorithm, that has been used to numerically cross-check the obtained results in 4, 6, and 8 dimensions.
We showcase the calculation of the master integrals needed for the two loop mixed QCD-QED virtual corrections to the neutral current Drell-Yan process $(q\bar{q}\rightarrow l^+ l^-)$. After establishing a basis of 51 master integrals, we cast the latter into canonical form by using the Magnus algorithm. The dependence on the lepton mass is then expanded such that potentially large logarithmic contributions are kept. After determining all boundary constants, we give the coefficients of the Taylor series around four space-time dimensions in terms of generalized polylogarithms up to weight four.
We present analytical expressions for the 31 five-particle phase-space master integrals in massless QCD as an $ε$-series with coefficients being multiple zeta values of weight up to 12. In addition, we provide a computer code for the Monte-Carlo integration in higher dimensions, based on the RAMBO algorithm, that has been used to numerically cross-check the obtained results in 4, 6, and 8 dimensions.
We make a detailed study on the $J/ψ$ meson longitudinal leading-twist distribution amplitude $ϕ_{2;J/ψ}^\|$ by using the QCD sum rules within the background field theory. By keeping all the non-perturbative condensates up to dimension-six, we obtain accurate QCD sum rules for the moments $\langleξ_{n;J/ψ}^\|\rangle$. The first three ones are $\langleξ_{2;J/ψ}^\|\rangle=0.083(12)$, $\langleξ_{4;J/ψ}^\|\rangle=0.015(5)$ and $\langleξ_{6;J/ψ}^\|\rangle=0.003(2)$, leading to a single peaked behavior for $ϕ_{2;J/ψ}^\|$ which is sharper than the previous ones around the region of $x\sim0.5$. As an …
Spin Dependence of Associated Production of a Prompt Photon and a Charm Quark at Next-to-Leading Order in QCD
本文用微扰量子色动力学的二阶方法$O(α^2_s)$计算了在大的激发光子和粲夸克的横动量下，两粒子包容反应$p + p \to γ+ c + X$的横截面与纵自旋的关系.微分分布提供的自旋平均截面和两个自旋纵向极化不对称$A_{LL}$在布鲁克海文相对论重离子对撞机的能量。本文还对确定粲夸克密度的自旋依赖性的前景作了评估。
We complete the analytic evaluation of the master integrals for the two-loop non-planar box diagrams contributing to the top-pair production in the quark-initiated channel, at next-to-next-to-leading order in QCD. The integrals are determined from their differential equations, which are cast into a canonical form using the Magnus exponential. The analytic expressions of the Laurent series coefficients of the integrals are expressed as combinations of generalized polylogarithms, which we validate with several numerical checks. We discuss the analytic continuation of the planar and the non-plana…
We discuss new ideas for consideration of loop diagrams and angular integrals in $D$-dimensions in QCD. In case of loop diagrams, we propose the covariant formalism of expansion of tensorial loop integrals into the orthogonal basis of linear combinations of external momenta. It gives a very simple presentation for the final results and is more convenient for calculations on computer algebra systems. In case of angular integrals we demonstrate how to simplify the integration of differential cross sections over polar angles. Also we derive the recursion relations, which allow to reduce all occur…
We show the 't Hooft Equation and the light-front holographic Schrödinger Equation are complementary to each other in governing the transverse and longitudinal dynamics of colour confinement in quark-antiquark mesons. Together, they predict remarkably well the light, heavy-light and heavy-heavy meson spectroscopic data. The universal emerging hadronic scale of light-front holography, $κ\approx 0.5$ GeV, controls the transverse dynamics of confinement in all mesons. In heavy-heavy mesons, it also coincides numerically with the 't Hooft coupling which governs longitudinal confinement, thus refle…
Fragmentation Functions in Next-To-Leading Order QCD
我们提出了一套新的碎裂函数在次领先阶QCD，确定从e+e-湮没数据的包容性粒子生产。除了O（alpha_s）非极化截面外，还利用纵向截面从e+e湮没数据中提取了胶子碎裂函数。由于对于纵向极化光子（或Z玻色子），O（alpha_s）为零，因此需要O（alpha_s^2）修正来减少尺度模糊性。最近，P. J. Rijken和W.L. van Neerven提出了次领先阶的纵向系数函数。我们在本文中确认了他们的部分结果，并通过与LEP 1数据进行一致比较所必须包括的色类C_F*T_R的结果完成了计算。然后使用一套完整的系数函数与新的数据从ALEPH确定带电强子的碎裂函数。这个集合，以及以前发表的带电π介子、K介子、D^* 介子和中性K介子的集合，可以用来检验e+e湮灭、光生、γ-γ碰撞、p-p_bar散射和DIS中的QCD。最后，我们建议如何利用改进的关于胶子碎裂的知识来确定光子的胶子和粲含量。
We present the analytic calculation of the Master Integrals for the two-loop, non-planar topologies that enter the calculation of the amplitude for top-quark pair hadroproduction in the quark-annihilation channel. Using the method of differential equations, we expand the integrals in powers of the dimensional regulator $ε$ and determine the expansion coefficients in terms of generalized harmonic polylogarithms of two dimensionless variables through to weight four.
We present the two-loop master integrals relevant to the ${\mathcal O}(αα_s)$-corrections to the decay $H \rightarrow b \bar{b}$ through a $H t \bar{t}$-coupling. We keep the full dependence on the heavy particle masses, but neglect the $b$-quark mass. The occurring square roots can be rationalised and the result is expressed in terms of multiple polylogarithms.
The longitudinal current density induced by the inhomogeneous electric field in the hot magnetized quark-gluon plasma has been investigated and utilized in obtaining the conductivity of the medium. The analysis has been done in the regime where inhomogeneity of the field is small so that the collision effect could be significant. The modeling of the QCD medium is based on a quasiparticle description where the medium effects have been encoded in the effective quarks, antiquarks and gluons. The temperature dependence of the linear longitudinal current density (in terms of the electric field) and…
The production of electroweak $Z$ bosons that decay to neutrinos and recoil against jets with large transverse momentum $p_\perp$ is an important background process to searches for dark matter at the Large Hadron Collider (LHC). To fully benefit from opportunities offered by the future high-luminosity LHC, the theoretical description of the $pp \to Z+j$ process should be extended to include mixed QCD-electroweak corrections. The goal of this paper is to initiate the computation of such corrections starting with the calculation of the Feynman integrals needed to describe two-loop QCD-electrowea…
The master integrals for the mixed QCD-QED two-loop virtual corrections to the charged-current Drell-Yan process $q\bar{q}^{\prime} \rightarrow \ell ν$ are computed analytically by using the differential equation method. A suitable choice of master integrals makes it successful to cast the differential equation system into the canonical form. We keep the dependence on charged lepton mass in the building of differential equations and then expand the system against the ratio of small charged lepton mass to large $W$-boson mass. In such a way the final results will contain large logarithms of the…
