Quark and Gluon Sivers Functions
The physics of hadron single transverse spin asymmetries is discussed. Possible measurements of both the quark and gluon Sivers functions are proposed.
hep-ph↗
arXiv subjects
Ivan Schmidt
Publications and source records attributed to Ivan Schmidt.
Effective action of dressed mean fields for N = 4 super-Yang-Mills theory
Based on general considerations such as $R$-operation and Slavnov-Taylor identity we show that the effective action, being understood as Legendre transform of the logarithm of the path integral, possesses particular structure in ${\cal N} =4$ supersymmetric Yang--Mills theory for kernels of the effective action expressed in terms of the dressed effective fields. These dressed effective fields have been introduced in our previous papers as actual variables of the effective action. The concept of dressed effective fields naturally appears in the framework of solution to Slavnov-Taylor identity. The particularity of the structure is the independence of these kernels on the ultraviolet regularization scale $Λ.$ These kernels are functions of mutual spacetime distances and of the gauge coupling. The fact that $β$ function in this theory is zero is used significantly.
hep-th↗
Scalar meson mediated nuclear mu-e conversion
We study the nuclear mu-e conversion in the general framework of the effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation (LFV). We analyze the role of scalar meson exchange between the lepton and nucleon currents and show its relevance for the coherent channel of mu-e conversion. We show that this mechanism introduces modifications in the predicted mu-e conversion rates in comparison with the conventional direct nucleon mechanism, based on the contact type interactions of the nucleon currents with the LFV leptonic current. We derive from the experimental data lower limits on the mass scales of the generic LFV lepton-quark contact terms and demonstrate that they are more stringent than the similar limits existing in the literature.
hep-ph↗
Large Rapidity Gap Processes in Proton-Nucleus Collisions
The cross sections for a variety of channels of proton-nucleus interaction associated with large gaps in rapidity are calculated within the Glauber-Gribov theory. We found inelastic shadowing corrections to be dramatically enhanced for such events. We employ the light-cone dipole formalism which allows to calculate the inelastic corrections to all orders of the multiple interaction. Although Gribov corrections are known to make nuclear matter more transparent, we demonstrate that in some instances they lead to an opaqueness. Numerical calculations are performed for the energies of the HERA-B experiment, and the RHIC-LHC colliders.
hep-ph↗
Recursive method to obtain the parametric representation of a generic Feynman diagram
A recursive algebraic method which allows to obtain the Feynman or Schwinger parametric representation of a generic L-loops and (E+1) external lines diagram, in a scalar $ϕ^{3}\oplus ϕ^{4}$ theory, is presented. The representation is obtained starting from an Initial Parameters Matrix (IPM), which relates the scalar products between internal and external momenta, and which appears explicitly when this parametrization is applied to the momentum space representation of the graph. The final product is an algorithm that can be easily programmed, either in a computer programming language (C/C++, Fortran,...) or in a symbolic calculation package (Maple, Mathematica,...).
hep-th↗
Shadowing and Antishadowing in Neutrino Deep Inelastic Scattering
The coherence of multiscattering quark nuclear processes leads to shadowing and antishadowing of the electromagnetic nuclear structure functions in agreement with measurements. This picture leads to substantially different antishadowing for charged and neutral current processes, particularly in anti-neutrino reactions, thus affecting the extraction of the weak-mixing angle $\sin^2θ_W$.
hep-ph↗
Breakdown of QCD factorization at large Feynman x
Recent measurements by the BRAHMS collaboration of high-pT hadron production at forward rapidities at RHIC found the relative production rate(d-Au)/(p-p) to be suppressed, rather than enhanced. Examining other known reactions (forward production of light hadrons, the Drell-Yan process, heavy flavor production, etc.), one notes that all of these display a similar property, namely, their cross sections in nuclei are suppressed at large xF. Since this is the region where x2 is minimal, it is tempting to interpret this as a manifestation of coherence, or of a color glass condensate, whereas it is actually a simple consequence of energy conservation and takes place even at low energies. We demonstrate that in all these reactions there is a common suppression mechanism that can be viewed, alternatively, as a consequence of a reduced survival probability for large rapidity gap processes in nuclei, Sudakov suppression, an enhanced resolution of higher Fock states by nuclei, or an effective energy loss that rises linearly with energy. Our calculations agree with data.
hep-ph↗
Collins Effect in Single Spin Asymmetries of the $p^{\uparrow}p \to πX$ Process
We investigate the Collins effect in single spin asymmetries (SSAs) of the $p^{\uparrow}p \to πX$ process, by taking into account the transverse momentum dependence of the microscopic sub-processes cross sections, with the transverse momentum in the Collins function integrated over. We find that the asymmetries due to the Collins effect can only explain the available data at best qualitatively, by using our choices of quark distributions in the quark-diquark model and a pQCD-based analysis, together with several options of the Collins function. Our results indicate the necessity to take into account contributions from other effects such as the Sivers effect or twist-3 contributions.
hep-ph↗
Transverse single spin asymmetries in photon production
Transverse single-spin asymmetries (SSA) in inclusive reactions are now considered to be directly related to the transverse momentum ${\bf k}_{T}$ of the fundamental partons involved in the process. We find that the ideal probe to extract information on the gluon Sivers function is the transverse SSA of prompt photon production $p p^{\uparrow} \to γX$, at large $p_T$. The following related processes, $p p^{\uparrow} \to γ+ jet + X$, $p p^{\uparrow} \to γ^* + X \to μ^+ μ^- + X$ and $\bar{p} p^{\uparrow} \to γ+ X$ are also briefly discussed.
hep-ph↗
Nuclear Antishadowing in Neutrino Deep Inelastic Scattering
The shadowing and antishadowing of nuclear structure functions in the Gribov-Glauber picture is due respectively to the destructive and constructive interference of amplitudes arising from the multiple-scattering of quarks in the nucleus. The effective quark-nucleon scattering amplitude includes Pomeron and Odderon contributions from multi-gluon exchange as well as Reggeon quark-exchange contributions. We show that the coherence of these multiscattering nuclear processes leads to shadowing and antishadowing of the electromagnetic nuclear structure functions in agreement with measurements. This picture leads to substantially different antishadowing for charged and neutral current reactions, thus affecting the extraction of the weak-mixing angle $θ_W$. We find that part of the anomalous NuTeV result for $θ_W$ could be due to the nonuniversality of nuclear antishadowing for charged and neutral currents. Detailed measurements of the nuclear dependence of individual quark structure functions are thus needed to establish the distinctive phenomenology of shadowing and antishadowing and to make the NuTeV results definitive.
hep-ph↗
Particle-Antiparticle Asymmetries of $Λ$ Production in Hadron-Nucleon Collisions
The particle-antiparticle asymmetries of $Λ$ production in 250 GeV/c $π^{\pm}$, $K^{\pm}$, and $p$ --nucleon collisions are studied with two model parametrizations of quark to $Λ$ fragmentation functions. It is shown that the available data can be qualitatively explained by the calculated results in both the quark-diquark model and a pQCD based analysis of fragmentation functions. The differences in the two model predictions are significant for $K^{\pm}$ beams, and high precision measurements of the asymmetries with detailed $x_F$ and $P_T$ information can discriminate between different predictions.
hep-ph↗
Effective Lagrangian approach to nuclear mu-e conversion and the role of vector mesons
We study nuclear mu-e conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation (LFV). We examine the impact of a specific hadronization prescription on the analysis of new physics in nuclear mu-e conversion and stress the importance of vector meson exchange between lepton and nucleon currents. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the phi meson. This allows us to extract new limits on the LFV lepton-quark effective couplings from the existing experimental data.
hep-ph↗
Vector mesons in nuclear mu-e conversion
We study nuclear mu-e conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation (LFV). We show that vector meson exchange between lepton and nucleon currents plays an important role in this process. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the phi meson. This allows us to extract new limits on the LFV lepton-quark effective couplings from the existing experimental data.
hep-ph↗
Ratio of $\barΛ/Λ$ in Semi-inclusive Electroproduction
It is shown that the $\barΛ/Λ$ cross section ratio in semi-inclusive electroproduction of $Λ$ and $\barΛ$ hyperons in deep inelastic scattering of charged lepton on a nucleon target, can provide useful information on the quark to $Λ$ fragmentation functions. This ratio is calculated explicitly in a quark-diquark model, a pQCD based analysis, and an SU(3) symmetry model, with three different options for the contribution from the unfavored fragmentation functions. The $x$-dependence of this ratio is sensitive to the ratio of unfavored fragmentation functions over favored fragmentation functions, $D_{\bar{u}}^Λ(z)/D_{u}^Λ(z)$, whereas the $z$-dependence is sensitive to the flavor structure of the fragmentation functions, i.e., the ratio $D_u^Λ(z)/D_s^Λ(z)$. Future measurements by the HERMES Collaboration at DESY can discriminate between various cases.
hep-ph↗
Review of Spectroscopic Determination of Extra Spatial Dimensions in the Early Universe
Atomic and molecular transitions for high Z objects in the early universe give bounds to the possible existence of extra spatial dimensions $D = 3+ε$. We review the theory and present observational data, based on Lyman and Balmer hydrogen transitions of distant quasars and CO rotational transitions of far away giant molecular clouds.
astro-ph↗
Searching for Extra Dimensions in the Early Universe
We investigate extra spatial dimensions ($D = 3+ε$) in the early universe using very high resolution molecular rotational spectroscopic data derived from a large molecular cloud containing moderately cold carbon monoxide gas at Z $\approx 6.42$. It turns out that the $ε$-dependent quantum mechanical wavelength transitions are solvable for a linear molecule and we present the solution here. The CO microwave data allows a very precise determination of $< ε> = -0.00000657 \pm .10003032$. The probability that $ < ε> \neq 0$ is one in 7794, only 850 million years (using the standard cosmology) after the Big Bang.
astro-ph↗
Mass Suppression in Octet Baryon Production
There is a striking suppression of the cross section for production of octet baryons in $e^+ e ^-$ annihilation, as the mass of the produced hadron increases. We present a simple parametrization for the fragmentation functions into octet baryons guided by two input models: the SU(3) flavor symmetry part is given by a quark-diquark model, and the baryon mass suppression part is inspired by the string model. We need only eight free parameters to describe the fragmentation functions for all octet baryons. These free parameters are determined by a fit to the experimental data of octet baryon production in $e^+ e ^-$ annihilation. Then we apply the obtained fragmentation functions to predict the cross section of the octet baryon production in charged lepton DIS and find consistency with the available experimental data. Furthermore, baryon production in $pp$ collisions is suggested to be an ideal domain to check the predicted mass suppression.
hep-ph↗
Transverse single-spin asymmetries in gauge boson production
Transverse single-spin asymmetries (SSA) in inclusive reactions are now considered to be directly related to the transverse momentum $k_{T}$ of the fundamental partons involved in the process. Several possible leading-twist QCD mechanisms have been proposed to explain the available data, in particular the Sivers effect which was resurrected recently. We show that from the measurement of transverse SSA in inclusive production of gauge bosons, one can learn more about the Sivers functions and possibly to achieve a reliable flavor separation.
hep-ph↗