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Mary Alberg

Publications and source records attributed to Mary Alberg.

18 recordsLinked to original sources
arXiv2024

Quark Counting, Drell-Yan West, and the Pion Wave Function

The relation between the pion's quark distribution function, $q(x)$, its light-front wave function, and the elastic charge form factor, $F(Δ^2)$ is explored. The square of the leading-twist pion wave function at a special probe scale, $ζ_H$, is determined using models and Poincare covariance from realistic results for $q(x)$. This wave function is then used to compute form factors with the result that the Drell-Yan-West and quark counting relationships are not satisfied. A new relationship between $q(x)$ and $F(Δ^2)$ is proposed.

hep-ph↗
arXiv2022

Pions in Proton Structure and Everywhere Else

The pion cloud is important in nuclear physics and in a variety of low-energy hadronic phenomena. We argue that it is natural to expect it to also be important in lepton-proton deep inelastic scattering and Drell-Yan studies of proton structure. We compute the necessary consequences of the pion cloud in connection with the recent SeaQuest data. The effects are detailed by using the exact kinematics of the experiment. Good agreement with the measurements is obtained. Thus the universality of pionic effects is understood.

nucl-th↗
arXiv2019

Chiral Light Front Perturbation Theory and the Flavor Dependence of the Light-Quark Nucleon Sea

The light-quark flavor dependence of the proton sea has been of great interest for many years because of its close connection with non-perturbative effects. One hypothesis is that this dependence arises from the pion cloud of the proton. We apply light cone perturbation theory and experimental constraints to a chiral Lagrangian to compute the relevant Fock-space components of the nucleon wave function with well-defined uncertainties. Existing experimental information regarding the light flavor sea is studied, and predictions for future experimental results are provided. Future experiments have the ability to rule out this hypothesis and have profound implications for understanding the nucleon-nucleon force.

nucl-th↗
arXiv2017

A Bayesian analysis of light-front models and the nucleon's charmed sigma term

We present the results of a recent analysis to study the nucleon's charm sigma term, $σ_{c\overline{c}}$. We construct a minimal model in terms of light-front variables and constrain the range of possibilities using extant knowledge from deeply inelastic scattering (DIS) and Bayesian parameter estimation, ultimately computing $σ_{c\overline{c}}$ in an explicitly covariant manner. We find a close correlation between a possible nonperturbative component of the charm structure function, $F^{c\overline{c}}_{2,\, \mathrm{IC}}$, and $σ_{c\overline{c}}$. Independent of prescription for the covariant relativistic quark-nucleon vertex, we determine $σ_{c\overline{c}}$ under several different scenarios for the magnitude of intrinsic charm (IC) in DIS, namely $\langle x \rangle_{c+\overline{c}} = 0.1\%$, $0.35\%$, and $1\%$, obtaining for these $σ_{c\overline{c}} = 4 \pm 4$, $12 \pm 13$, and $32 \pm 34$ MeV, respectively. These results imply the existence of a reciprocity between the IC parton distribution function (PDF) and $σ_{c\overline{c}}$ such that new information from either DIS or improved determinations of $σ_{c \overline{c}}$ could significantly impact constraints to the charm sector of the proton wave function.

hep-ph↗
arXiv2016

A Euclidean bridge to the relativistic constituent quark model

${\bf Background}$ Knowledge of nucleon structure is today ever more of a precision science, with heightened theoretical and experimental activity expected in coming years. At the same time, a persistent gap lingers between theoretical approaches grounded in Euclidean methods (e.g., lattice QCD, Dyson-Schwinger Equations [DSEs]) as opposed to traditional Minkowski field theories (such as light-front constituent quark models). ${\bf Purpose}$ Seeking to bridge these complementary worldviews, we explore the potential of a Euclidean constituent quark model (ECQM). This formalism enables us to study the gluonic dressing of the quark-level axial-vector vertex, which we undertake as a test of the framework. ${\bf Method}$ To access its indispensable elements with a minimum of inessential detail, we develop our ECQM using the simplified quark $+$ scalar diquark picture of the nucleon. We construct a hyperspherical formalism involving polynomial expansions of diquark propagators to marry our ECQM with the results of Bethe-Salpeter Equation (BSE) analyses, and constrain model parameters by fitting electromagnetic form factor data. ${\bf Results}$ From this formalism, we define and compute a new quantity --- the Euclidean density function (EDF) --- an object that characterizes the nucleon's various charge distributions as functions of the quark's Euclidean momentum. Applying this technology and incorporating information from BSE analyses, we find the dressing effect on the proton's axial-singlet charge to be small in magnitude and consistent with zero. ${\bf Conclusions}$ The scalar quark $+$ diquark ECQM is a step toward a realistic quark model in Euclidean space, and urges additional refinements. The small size we obtain for the impact of the dressed vertex on the axial-singlet charge suggests that models without this effect are on firm ground to neglect it.

nucl-th↗
arXiv2016

The Role of Nucleon Strangeness in Supernova Explosions

Recent hydrodynamical simulations of supernova (SN) evolution have highlighted the importance of a thorough control over microscopic physics responsible for such internal processes as neutrino heating. In particular, it has been suggested that modifications to the neutrino-nucleon elastic cross section can potentially play a crucial role in producing successful supernova explosions. One possible source of such corrections can be found in a nonzero value for the nucleon's strange helicity content $Δs$. In the present analysis, however, we show that theoretical and experimental progress over the past decade has suggested a comparatively small magnitude for $Δs$, such that its sole effect is not sufficient to provide the physics leading to supernova explosions.

astro-ph.HE↗
arXiv2015

Constraining nucleon strangeness

Determining the nonperturbative $s\bar{s}$ content of the nucleon has attracted considerable interest and been the subject of numerous experimental searches. These measurements used a variety of reactions and place important limits on the vector form factors observed in parity-violating (PV) elastic scattering and the parton distributions determined by deep inelastic scattering (DIS). In spite of this progress, attempts to relate information obtained from elastic and DIS experiments have been sparse. To ameliorate this situation, we develop an interpolating model using light-front wave functions capable of computing both DIS and elastic observables. This framework is used to show that existing knowledge of DIS places significant restrictions on our wave functions. The result is that the predicted effects of nucleon strangeness on elastic observables are much smaller than those tolerated by direct fits to PV elastic scattering data alone. Using our model, we find $-0.024 \le μ_s \le 0.035$, and $-0.137 \le ρ^D_s \le 0.081$ for the strange contributions to the nucleon magnetic moment and charge radius. The model we develop also independently predicts the nucleon's strange spin content $Δs$ and scalar density $\langle N| \bar{s}s | N \rangle$, and for these we find agreement with previous determinations.

nucl-th↗
arXiv2013

Alberg and Miller Reply to arXiv:arXiv:1206.3671

In a recent Comment [arXiv:1206.3671] on our calculation of the pion contributions to the self-energy of the nucleon [arXiv:1201.4184], Ji, Melnitchouk and Thomas (JMT) correctly state that we obtain the same result as given by the pseudovector (PV) theory. We point out that this result is expected by the equivalence theorem, since our pion-nucleon effective theory puts the intermediate nucleon on its mass shell. We make no claim that pseudoscalar (PS) and pseudovector interactions are equivalent in general. JMT also argue that our theory will not give the correct PV result for the pion momentum distribution $f^N_π$. We note that the discrepancies are much smaller than the uncertainties due to $πN$ form factors. To summarize, nothing in the Comment by JMT changes the conclusions or numerical results of our work in any substantive way.

nucl-th↗
arXiv2012

Taming the Pion Cloud of the Nucleon

We present a light-front determination of the pionic contribution to the nucleon self-energy, $Σ_π$, to second-order in pion-baryon coupling constants that allows the pion-nucleon vertex function to be treated in a model-independent manner constrained by experiment. The pion mass $μ$ dependence of $Σ_π$ is consistent with chiral perturbation theory results for small values of $μ$ and is also linearly dependent on $μ$ for larger values, in accord with the results of lattice QCD calculations. The derivative of $Σ_π$ with respect to $μ^2$ yields the dominant contribution to the pion content, which is consistent with the $\bar{d}-\bar{u}$ difference observed experimentally in the violation of the Gottfried sum rule.

nucl-th↗
arXiv2011

Comparison of kaon and pion valence quark distributions in a statistical model

We have calculated the Bjorken-x dependence of the kaon and pion valence quark distributions in a statistical model. Each meson is described by a Fock state expansion in terms of quarks, antiquarks and gluons. Although Drell-Yan experiments have measured the pion valence quark distributions directly, the kaon valence quark distributions have only been deduced from the measurement of the ratio $\bar{u}_K(x)/\bar{u}_π(x)$. We show that, using no free parameters, our model predicts the decrease of this ratio with increasing x.

nucl-th↗
arXiv2011

Perturbative and Non-Perturbative Origins of the Proton Sea

Deep Inelastic Scattering and Drell-Yan experiments have measured a light flavor asymmetry in the proton sea. The excess of dbar over ubar quarks can be understood in many models, but the ratio dbar(x)/ubar(x) measured by Fermilab E866 has not been successfully described. Fermilab E-906 will probe the kinematic dependence of this ratio with better resolution and extend it to higher x. We have developed a hybrid model that includes both perturbative and non-perturbative contributions to the proton sea. A meson cloud formalism is used to represent the non-perturbative fluctuation of the proton into meson-baryon states. We include perturbative processes by using a statistical model that uses Fock states of quarks, antiquarks and gluons to represent the parton distributions of the 'bare' hadrons in the meson cloud. We compare our results to the E866 data.

nucl-th↗
arXiv2004

Renormalization of the singular attractive $1/r^4$ potential

We study the radial Schrödinger equation for a particle of mass $m$ in the field of a singular attractive $g^2/{r^4}$ potential with particular emphasis on the bound states problem. Using the regularization method of Beane \textit{et al.}, we solve analytically the corresponding ``renormalization group flow" equation. We find in agreement with previous studies that its solution exhibits a limit cycle behavior and has infinitely many branches. We show that a continuous choice for the solution corresponds to a given fixed number of bound states and to low energy phase shifts that vary continuously with energy. We study in detail the connection between this regularization method and a conventional method modifying the short range part of the potential with an infinitely repulsive hard core. We show that both methods yield bound states results in close agreement even though the regularization method of Beane \textit{et al.} does not include explicitly any new scale in the problem. We further illustrate the use of the regularization method in the computation of electron bound states in the field of neutral polarizable molecules without dipole moment. We find the binding energy of s-wave polarization bound electrons in the field of C$_{60}$ molecules to be 17 meV for a scattering length corresponding to a hard core radius of the size of the molecule radius ($\sim 3.37$ Å). This result can be further compared with recent two-parameter fits using the Lennard-Jones potential yielding binding energies ranging from 3 to 25 meV.

quant-ph↗
arXiv2003

Parton distributions in the proton and pion

We use detailed balance for a hadron composed of quark and gluon Fock states to obtain parton distributions in the proton and pion on the basis of a simple statistical model.

hep-ph↗
arXiv1999

Light quark distributions in the proton sea

We use the meson cloud model to calculate $\bar{d}(x) - \bar{u}(x)$ and $ \bar{d}(x)/\bar{u}(x)$ in the proton. We show that a modification of the symmetric, perturbative part of the light quark sea provides better agreement with the ratio $ \bar{d}(x)/\bar{u}(x).

hep-ph↗
arXiv1999

Omega Meson Cloud and the Proton's Light Anti-Quark Distribution

We use the meson cloud model of the nucleon to calculate distribution functions for $(\bar {d} - \bar{u})$ and $ \bar{d}/\bar{u}$ in the proton. Including the effect of the omega meson cloud, with a coupling constant $g_ω^2/4π\approx 8$, allows a reasonably good description of the data.

hep-ph↗
arXiv1998

The Quark Distributions in the Σ^+ Hyperon

We use the meson cloud model and the Sullivan mechanism to estimate the sea flavor asymmetry in the Σ^+ baryon and calculate the distribution functions of both sea and valence quarks. We find large deviations from SU(3).

hep-ph↗
arXiv1996

Determination of flavor asymmetry for $Σ^{\pm}$ by the Drell-Yan process

Flavor asymmetries for the valence and sea quarks of the $Σ^{\pm}$ can be obtained from Drell-Yan experiments using charged hyperon beams on proton and deuteron targets. A large, measurable difference in sea quark asymmetries is predicted between SU(3) and pseudoscalar meson models. The latter predict that in $Σ^{+}$, $\bar{u}/\bar{d} \leq 1/2$, whereas the former predict $\bar{u}/\bar{d} \approx 4/3$. Estimates of valence quark asymmetries based on quark models also show large deviations from SU(3) predictions, which should be measurable.

hep-ph↗