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Ivan Schmidt

Publications and source records attributed to Ivan Schmidt.

268 records · Page 15Linked to original sources
arXiv1999

Extra Dimensions in the Early Universe

We investigate the possible occurrence of extra spatial dimensions (D = 3+epsilon) in the early universe. A detailed calculation is presented which shows that the crucial signal is the apparent inequality of the cosmological Z-term between matching Lyman alpha (Ly{alpha}) and Lyman beta (Ly{beta}) spectral lines, both emission and absorption, when using the present epoch (laboratory) wavelengths. We present preliminary upper limits to the value of epsilon, to be improved by direct, more careful analysis of the spectra. We take catalogued quasar Ly{alpha} forest data and perform Student's t-test to determine whether we should reject the null hypothesis (no fractal dimensions). Finally, a chi^{2} analysis is done for fitting epsilon in the early universe. The statistical tests and experimental data are all consistent with epsilon = 0 for Z < 3.3, but the experimental data support non-zero epsilon values for Z > 4. However, it should be emphasized that the non-zero values of epsilon found for Z > 4 may be due to undiscovered systematic errors in the original data.

hep-ph↗
arXiv1999

Quark Structure of $Λ$ from $Λ$-Polarization in Z Decays

The flavor and spin structure for the quark distributions of the $Λ$-baryon is studied in a perturbative QCD (pQCD) analysis and in the SU(6) quark-diquark model, and then applied to calculate the $Λ$-polarization of semi-inclusive $Λ$ production in $e^+e^-$-annihilation near the $Z$-pole. It is found that the quark-diquark model gives very good description of the available experimental data. The pQCD model can also give good description of the data by taking into account the suppression of quark helicities compared to the naive SU(6) quark model spin distributions. Further information is required for a clean distinction between different predictions concerning the flavor and spin structure of the $Λ$.

hep-ph↗
arXiv1999

QCD condensate contributions to the effective quark potential in a covariant gauge

We discuss QCD condensate contributions to the gluon propagator both in the fixed-point gauge and in covariant gauges for the external QCD vacuum gluon fields with the conclusion that a covariant gauge is essential to obtain a gauge invariant QCD vacuum energy density difference and to retain the unitarity of the quark scattering amplitude. The gauge-invariant QCD condensate contributions to the effective one-gluon exchange potential are evaluated by using the effective gluon propagator which produces a gauge-independent quark scattering amplitude.

hep-ph↗
arXiv1998

The Quark Spin Distributions of the Nucleon

The quark helicity measured in polarized deep inelastic scattering is different from the quark spin in the rest frame of the nucleon. We point out that the quark spin distributions $Δq_{RF}(x)$ are connected with the quark helicity distributions $Δq(x)$ and the quark transversity distributions $δq(x)$ by an approximate relation: $Δq_{RF}(x) + Δq(x)=2 δq(x)$. This relation will be useful in order to measure the rest frame (or quark model) spin distributions of the nucleon once the quark helicity distributions and quark transversity distributions are themselves measured. We also calculate the $x$-dependent quark transversity distributions $δq(x)$ and quark spin distributions $Δq_{RF}(x)$ in a light-cone SU(6) quark-spectator model, and present discussions on possible effect from the sea quark-antiquark pairs.

hep-ph↗
arXiv1998

The Quark Orbital Angular Momentum in a Light-Cone Representation

We perform an analysis of the quark angular momentum in a light-cone representation by taking into account the effect due to the Melosh-Wigner rotation and find that there is a relativistic correction factor connecting the quark orbital angular momentum with the quark model spin distribution: $L_q(x)={ }Δq_{QM}(x)$. The quark orbital angular momentum $L_q(x)$ and the quark helicity distribution $Δq(x)$ are connected to the quark model spin distribution $Δq_{QM}(x)$ by a relation: $\frac{1}{2}Δq(x)+ L_q(x)=\frac{1}{2}Δq_{QM}(x)$, which means that one can decompose the quark model spin contribution $Δq_{QM}(x)$ by a quark helicity term $Δq(x)$ {\it plus} an orbital angular momentum term $L_q(x)$. There is also a new relation connecting the quark orbital angular momentum with the measurable quark helicity distribution and transversity distribution ($δq(x)$): $Δq(x)+L_q(x)=δq(x)$, from which we may have new sum rules connecting the quark orbital angular momentum with the nucleon axial and tensor charges.

hep-ph↗
arXiv1998

The Spin Structure of a Polarized Photon

We show that the first moment of the spin-dependent structure function $g_1^γ(x,Q^2)$ of a real photon vanishes independent of the momentum transfer $Q^2$ it is probed with. This result is non-perturbative: it holds to all orders in perturbation theory in abelian and non-abelian gauge theory and at every twist.

hep-ph↗
arXiv1997

Polarization Asymmetry Zero in Heavy Quark Photoproduction and Leptoproduction Cross Sections

We demonstrate two novel features of the sea-quark contributions to the polarized structure functions and photoproduction cross sections, a zero sum rule and a zero crossing point of the polarization asymmetry, which can be traced directly to the dynamics of the perturbative tree-graph gluon-splitting contributions. In particular, we show that the Born contribution of massive quarks arising from photon-gluon fusion gives zero contribution to the logarithmic integral over the polarization asymmetry $\int {dν\over ν}Δσ(ν,Q^2)$ for any photon virtuality. The vanishing of this integral in the Bjorken scaling limit then implies a zero gluon-splitting Born contribution to the Gourdin-Ellis-Jaffe sum rule for polarized structure functions from massive sea quarks. The vanishing of the polarization asymmetry at or near the canonical position predicted by perturbative QCD provides an important tool for verifying the dominance of the photon-gluon fusion contribution to charm photoproduction and for validating the effectiveness of this process as a measure of the gluon polarization $ΔG(x,Q^2)$ in the nucleon. The displacement of the asymmetry zero from its canonical position is sensitive to the virtuality of the gluon in the photon-gluon fusion subprocess, and it can provide a measure of intrinsic and higher-order sea quark contributions.

hep-ph↗
arXiv1997

New Sum Rules for Nucleon Tensor Charges

Two new sum rules for the quark tensor charges of the nucleon are proposed, based on a relation connecting the quark transversity distributions to the quark helicity distributions and the quark model spin distributions, and on the sum rules for the quark helicity distributions. The two sum rules are useful for an estimate of the values of the quark tensor charges $δU$ and $δD$ from the measured quantities of $Γ^p$, $Γ^n$, $g_A/g_V$ and $ΔS$, and two model correction factors with limited uncertainties. We predict a small value for the sum of the quark tensor charges compared to most other predictions, in analogy to the unexpectedly small quark helicity sum which gave rise to the proton ``spin puzzle''.

hep-ph↗
arXiv1997

QCD Constrains on the Shape of Polarized Quark and Gluon Distributions

We develop simple analytic representations of the polarized quark and gluon distributions in the nucleon at low $Q^2$ which incorporate general constraints obtained from the requirements of color coherence of gluon couplings at $x \sim 0$ and the helicity retention properties of perturbative QCD couplings at $x \sim 1.$ The unpolarized predictions are similar to the $D_0'$ distributions given by Martin, Roberts, and Stirling. The predictions for the quark helicity distributions are compared with polarized structure functions measured by the E142 experiment at SLAC and the SMC experiment at CERN.

hep-ph↗
arXiv1997

Antihydrogen

CERN announced in January 1996 the detection of the first eleven atoms of antimatter ever produced. The experiment was based on a method proposed earlier by S. Brodsky, C. Munger and I. Schmidt, and which furthermore predicted exactly the number of atoms that were detected for the particular conditions of the experiment. The study of antihydrogen affords science the opportunity to continue research on the symmetry between matter and antimatter. In this talk the importance of antihydrogen as a basic physical system is discussed. Different production methods that have been tried in the past are briefly presented, and the method that was used in the CERN experiment is analyzed in detail. It consists in producing antihydrogen by circulating a beam of an antiproton ring through an internal gas target. In the Coulomb field of a nucleus, an electron-positron pair is created, and antihydrogen will form when the positron is created in a bound rather that a continuum state about the antiproton. The theoretical calculation of the production cross section is presented in detail. A discussion of the detection systems used both in the CERN experiment and in another similar experiment that is right now underway at Fermilab are also given. Finally I present and discuss possible future experiments using antihydrogen, including the measurement of the antihydrogen Lamb shift.

hep-ph↗
arXiv1995

W ANOMALOUS MOMENTS AND THE POLARIZATION ASYMMETRY ZERO IN gamma e --> W nu

We show from general principles that there must be a center of mass energy, $\sqrt s_0$, where the polarization asymmetry $A=Δσ({γe \to W ν})/ σ({γe \to W ν})$ for circularly-polarized photon and electron beams vanishes. In the case of the Standard Model, the crossing point where the asymmetry changes sign occurs in Born approximation at $\sqrt s_{γe} = 3.1583\ldots M_W \simeq 254$ GeV. We demonstrate the sensitivity of the position of the polarization asymmetry zero to modifications of the SM trilinear $γW W$ coupling. Given reasonable assumptions for the luminosity and energy range for the Next Linear Collider(NLC) with a backscattered laser beam, we show that the zero point, $\sqrt s_0$, of the polarization asymmetry may be determined with sufficient precision to constrain the anomalous couplings of the $W$ to better than the 1\% level at $95\%$ CL. In addition to the fact that only a limited range of energy is required, the polarization asymmetry measurements have the important advantage that many of the systematic errors cancel in taking cross section ratios. The position of the zero thus provides an additional weapon in the arsenal used to probe anomalous trilinear gauge couplings.

hep-ph↗
arXiv1995

CLASSICAL PHOTOABSORPTION SUM RULES

We use a quantum loop expansion to derive sum rule constraints on polarized photoabsorption cross sections in the Standard Model, generalizing earlier results obtained by Altarelli, Cabibbo, and Maiani. We show that the logarithmic integral of the spin-dependent photoabsorption cross section $\int^\infty_{ν_{th}} {dν\over ν} Δσ_{\rm Born}(ν) $ vanishes for any $2 \to 2$ Standard Model or supersymmetric process $γa \to b c$ in the classical, tree-graph approximation. Here $ν= {p \cdot q}/M$ and $Δσ(ν) = σ_P(ν)- σ_A(ν)$ is the difference between the photoabsorption cross section for parallel and antiparallel photon and target helicities. Tests of the sum rule for the reactions $γe \to W ν$ and $γγ\to W^+ W^-$ can provide new tests of the canonical magnetic and quadrupole couplings of the Standard Model. We also extend the sum rule to certain virtual photon processes.

hep-ph↗
arXiv1994

Platelet Collapse Model of Pulsar Glitches

A platelet collapse model of starquakes is introduced. It displays self-organized criticality with a robust power-law behavior. The simulations indicate a near-constant exponent, whenever scaling is present.

astro-ph↗