Soft Contributions Research Articles

X‐Ray Emission from Middle‐aged Pulsars

We present a simple, unified model which accounts for properties of the X-ray emission from the three middle-aged pulsars PSR 1055-52, PSR 0656+14 and PSR 0630+18 (Geminga). The X-ray radiation from these objects is pulsed more strongly at energies above a transition point around 0.5 keV. In addition, the phase of the pulses shifts by about 80-100 degrees around the same point. Geminga also has the peculiarity that its pulsed fraction decreases in the 0.3-0.5 keV energy range, attaining a minimum near 0.5 keV. We show that a two-component hydrogen atmosphere is able to account for these disparate features. In our model, the hotter component is powered by particle bombardment and is restricted to the polar regions, while the cooler one covers the entire stellar surface. The two components also differ in their emission patterns, with the hard and soft contributions coming from areas radiating into fan and pencil beams, respectively.

Outside Money in the 2000 Presidential Primaries and Congressional General Elections

Beginning with the 1996 election cycle, political parties and interest groups, through soft money and issue advocacy, have mounted substantial campaigns in competitive elections. Noncandidate campaigns, funded with this outside money, are in some ways extensions of independent expenditure campaigns. However, by avoiding the words of express advocacy, as defined by the Supreme Court, groups may avoid the disclosure requirements imposed on independent expenditures. Party soft money contributions are disclosed but spending is unlimited.

Higgs production in hadron collisions: soft and virtual QCD corrections at NNLO

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. Using the recently evaluated two-loop amplitude for this process and the corresponding factorization formulae for soft-gluon bremsstrahlung at O(alpha_s^2), we compute the soft and virtual contributions to the NNLO cross section. We also discuss soft-gluon resummation at next-to-next-to-leading logarithmic accuracy. Numerical results for Higgs boson production at the LHC are presented.

Combining QCD matrix elements at next-to-leading order with parton showers in electroproduction

We present a method to combine next-to-leading order (NLO) matrix elements in QCD with leading logarithmic parton showers by applying a suitably modified version of the phase-space-slicing method. The method consists of subsuming the NLO corrections into a scale-dependent phase-space-slicing parameter, which is then automatically adjusted to cut out the leading order, virtual, soft and collinear contributions in the matrix element calculation. In this way a positive NLO weight is obtained, which can be redistributed by a parton shower algorithm. As an example, we display the method for single-jet inclusive cross sections at $\mathcal{O}({\ensuremath{\alpha}}_{s})$ in electroproduction. We numerically compare the modified version of the phase-space-slicing method with the standard approach and find very good agreement on the percent level.

Hard and soft contributions in diffraction: a closer look

Disentangle the hard and soft dynamics in diffractive DIS is one of the main open questions of the strong interactions. We propose the study of the logarithmic slope in Q 2 of the diffractive structure function as a potential observable to discriminate between the Regge and the QCD-based approaches. Our results indicate that a future experimental analyzes could evidentiate the leading dynamics at ep diffractive processes in the HERA kinematical regime.

Pion form factor and quark mass evolution in a light-front Bethe-Salpeter model

We discuss the soft contribution to the elastic pion form factor with the mass evolution from current to constituent quark being taken into account using a light-front Bethe-Salpeter (LFBS) model, which is a light-front quark model (LFQM) with a running mass. It is shown that partial conservation of the axial-vector current (PCAC) is satisfied with a running quark mass. We examine the sensitivity of the pion form factor using two different functional forms of the quark propagator. The Ball-Chiu ansatz is used to maintain local gauge invariance of the quark-photon vertex. The extension of our model to the hard contribution is also discussed.

Checkbook democracy: how money corrupts political campaigns

Counts are being taken before the political conventions convene: not delegates, but dollars. Public officials court donors more than voters, while the party faithful rally around the war chest rather than the platform. Virtually anything goes in campaign finance today, and, as a result, the electoral process is being hijacked by large contributions, secret influence, and increasingly unaccountable government leaders. In this lively and provocative book, Darrell M. West looks at how politics became such a money chase, why money has become such a pernicious influence on public debate, and what can be done to redeem the corrupted system. Drawing on interviews, memoirs, press coverage, legal depositions, and government documents, West's timely book investigates recent examples of campaign abuses to illustrate how political parties and organizations circumvent post-Watergate reform legislation -- and how money has become the key to winning elections and influencing the public. Included in his probe are such cases as the infamous Willie Horton ad in the 1988 presidential campaign, the Christian Action Network, Asian contributions to the Democrats, tobacco company donations to the Republicans, and President Clinton's 1996 campaign infractions. The numerous case studies expose the manifold loopholes and problems in current campaign finance laws, including soft money contributions, independent expenditures, issue advocacy, foreign contributions, and political activism by non-profit organizations. West's sober evaluation of the exploding costs of campaigns -- and escalating cynicism among voters -- offers a hard-hitting look at the forces working against reform and makes constructiveproposals for reversing this disconcerting trend in contemporary American politics.

Energy and fat intakes of children and adolescents in the United States: data from the National Health and Nutrition Examination Surveys

Dietary factors related to body weight and chronic disease risk are of interest because of recent increases in the prevalence of overweight. Secular trends in energy and fat intakes of youths aged 2-19 y were assessed. Current intakes were compared with recommendations. Dietary 24-h recall data from the third National Health and Nutrition Examination Survey (1988-1994) and earlier national surveys were examined. Mean energy intake changed little from the 1970s to 1988-1994 except for an increase among adolescent females. Over the same time period, the mean percentage of energy from total and saturated fat decreased, but remained above recommendations, with overall means of 33.5% of energy from fat and 12.2% of energy from saturated fat. In 1988-1994, approximately 1 in 4 youths met the recommendations for intakes of fat and saturated fat and 3 in 4 met the recommendation for cholesterol intake. Beverages contributed 20-24% of energy across all ages and soft drinks provided 8% of energy in adolescents. Except for adolescent girls, beverage energy contributions were generally higher among overweight than nonoverweight youths; soft drink energy contribution was higher among overweight youths than among nonoverweight youths for all groups. The lack of evidence of a general increase in energy intake among youths despite an increase in the prevalence of overweight suggests that physical inactivity is a major public health challenge in this age group. Efforts to increase physical activity and decrease nonnutritive sources of energy may be important approaches to counter the rise in overweight prevalence.

Angular pattern of minijet transverse energy flow in hadron and nuclear collisions

The azimuthal asymmetry of a minijet system produced at the early stage of nucleon–nucleon and nuclear collisions in a central rapidity window is studied. We show that in pp collisions the minijet transverse energy production in a central rapidity window is essentially unbalanced in the azimuth due to asymmetric contributions in which only one minijet hits the acceptance window. We further study the angular pattern of the transverse energy flow generated by the semihard degrees of freedom at the early stage of high energy nuclear collisions and its dependence on the number of semihard collisions in the models both including and neglecting soft contributions to the inelastic cross section at RHIC and LHC energies as well as on the choice of the infrared cutoff.

Light vector meson photoproduction at large t

We have studied in perturbative QCD all independent helicity amplitudes describing the photoproduction of light vector mesons at large t. We found a new hard production mechanism which is related to the possibility for a real photon to fluctuate into a massless q q ̄ pair in a chiral-odd spin configuration. Each helicity amplitude is given as a sum of a usual chiral-even contribution (when the helicities of quark and antiquark are antiparallel) and this additional chiral-odd part (where the helicities of quark and antiquark are parallel). The chiral-odd contribution is large, it leads to a dominance of the non spin-flip amplitude in a very broad region of intermediately high | t|. All amplitudes are expressed in terms of short distance asymptotics of the light-cone wave functions of vector meson (photon). We demonstrate that for each helicity amplitude there exists a soft non-factorizable contribution. We give arguments that for dominant non spin-flip helicity amplitude the relative contribution of the soft nonfactorizable interactions is numerically not large.

Pion form factor in QCD at intermediate momentum transfers

We present a quantitative analysis of the electromagnetic pion form factor in the light-cone sum rule approach, including radiative corrections and higher-twist effects. The comparison to the existing data favors the asymptotic profile of the pion distribution amplitude and allows to estimate the deviation: $(\int du/u \phi_\pi(u))/ (\int du/u \phi^{\rm as}_\pi(u))=$ 1.1$\pm$ 0.1 at the scale 1 GeV. Special attention is payed to the precise definition and interplay of soft and hard contributions at intermediate momentum transfer, and to matching of the sum rule to the perturbative QCD prediction. We observe a strong numerical cancellation between the soft (end point) contribution and power suppressed hard contributions of higher twist, so that the total nonperturbative correction to the usual pQCD result turns out to be of order 30% for $Q^2\sim 1$ GeV$^2$.

Radiation pions in two-nucleon effective field theory

For interactions involving two or more nucleons it is useful to divide pions into three classes: potential, radiation, and soft. The momentum threshold for the production of radiation pions is Q r= M Nm π . We show that radiation pions can be included systematically with a power counting in Q r . The leading order radiation pion graphs which contribute to NN scattering are evaluated in the PDS and OS renormalization schemes and are found to give a small contribution. The power counting for soft pion contributions is also discussed.

Soft contributions to hard pion photoproduction

Hard, or high transverse momentum, pion photoproduction can be a tool for probing the parton structure of the beam and target. We estimate the soft contributions to this process, with an eye toward delineating the region where perturbatively calculable processes dominate. Our soft process estimate is based on vector meson dominance and data based parameterizations of semiexclusive hadronic cross sections. We find that soft processes dominate in single pion photoproduction somewhat past 2 GeV transverse momentum at a few times 10 GeV incoming energy. The recent polarization asymmetry data is consistent with the perturbative asymmetry being diluted by polarization insensitive soft processes. Determining the polarized gluon distribution using hard pion photoproduction appears feasible with a few hundred GeV incoming energy (in the target rest frame).

Soft Pions at High Energy as an Origin of Flavor Asymmetry of the Light Sea Quarks in the Nucleon

By using the soft pion theorem in the inclusive reactions, soft pions' contribution to the structure function $F_2$ in the nucleon is estimated. It is shown that this contribution produces such a large flavor asymmetry in the light sea quark distributions that it gives about $30\sim 50 %$ of the NMC deficit in the Gottfried sum.

Soft and hard contributions to hard pion photoproduction

Soft and hard contributions to hard pion photoproduction

Self-diffusion coefficient equation for polyatomic fluid

An equation for the self-diffusion coefficient in a polyatomic fluid is presented as a sum of three friction coefficient terms: the temperature-dependent hard-sphere contribution, the chain contribution and the soft contribution. This equation has been developed by using the molecular dynamics simulation data for the HS chain fluid and the expression for the Lennard–Jones (LJ) fluid proposed by Ruckenstein and Liu. The real nonspherical compounds are modeled as chains of tangent LJ segments. The segment diameter σ LJ, segment–segment interaction energy ε LJ and chain length N (the number of segments) are obtained from the experimental diffusion data. The equation reproduces the experimental self-diffusion coefficients with an average absolute deviation (AAD) of 3.72% for 22 polyatomic compounds (1081 data points) over wide ranges of temperature and pressure. The results have been compared with that of the rough LJ (RLJ) equation. To minimize the number of the fitting parameters, the energy parameter ε LJ is estimated using a correlation obtained from viscosity data. The equation with two parameters gives an AAD of 4.72%.

An investigation of a possible hard contribution to φ photoproduction

We investigate the possibility that the process of φ photoproduction may have a significant hard perturbative QCD component. This suggestion is based on a study of the energy dependence of the forward φ photoproduction cross section followed by a calculation where we show that a coherent sum of the pQCD and conventional soft Pomeron contributions provides an excellent reproduction of the experimental data. Our results suggest that the transition from the predominantly soft photoproduction of light ρ and ω vector mesons to the predominantly hard photoproduction of heavy J/ Ψ and ϒ is smooth and gradual, similar to the transition observed in deep inelastic scattering studies of the proton structure function in the small x limit. Our predictions for higher HERA energies are presented.

Charge transfer vibronic excitons in ferroelectric oxides: experiment and theory

Review of the charge transfer vibronic excitons (CTVE) study on the basis of optical response investigations in ferroelectric oxides is presented. CTVE is the correlated pair of electron and hole small polarons whose stability is controlled by a pair pseudo-Jahn–Teller effect. The study is focused on the CTVE-induced critical dependence near the ferroelectric phase transition. The critical effect in absolute diffraction efficiency (ADE) formation of the laser-induced transient gratings near ferroelectric phase transition in KTa 1− x Nb x O 3 (KTN) is considered as an example. Critical concentration dependence for slow as well as for instantaneous (fast) optical response was detected. The peak positions for these x – dependences were different. The CTVE-model can explain these experiments taking into account not only the soft TO phonon mode contribution but also that of soft tunnel quasilocal modes of clusters of the second component.

Deeply virtual electroproduction of photons and mesons on the nucleon: Leading order amplitudes and power corrections

We estimate the leading order amplitudes for exclusive photon and meson electroproduction reactions at large Q^2 in the valence region in terms of skewed quark distributions. As experimental investigations can currently only be envisaged at moderate values of Q^2, we estimate power corrections due to the intrinsic transverse momentum of the partons in the meson wavefunction and in the nucleon. To this aim the skewed parton distribution formalism is generalized so as to include the parton intrinsic transverse momentum dependence. Furthermore, for the meson electroproduction reactions, we calculate the soft overlap type contributions and compare with the leading order amplitudes. We give first estimates for these different power corrections in kinematics which are relevant for experiments in the near future.

Radiative corrections to e+e− → H+H−: THDM versus MSSM

One-loop radiative corrections to e + e − → H + H − are considered at future linear collider energies, in the general type II Two Higgs Doublet Model (THDM) and in the Minimal Supersymmetric Standard Model-like (MSSM) Higgs sector. To make the comparison between THDM and MSSM tractable, we have introduced a quasi-SUSY parameterization which preserves all the tree-level Higgs mass-sum-rules of the MSSM, and involves just 3 free parameters in the Higgs sector (instead of 7 in the general THDM) and comprises the MSSM as a particular case. The model-independent soft photon contribution is isolated and shown to be substantial. Important effects come also from the contribution of the model dependent h 0 H + H − and H 0 H + H − vertices to the final state. In the MSSM, the contribution of the Higgs sector is moderate (a few percent) while in the THDM and both for small and large tan β important effects (∼ + 30%) can be found.