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LCLS-II New Instruments Workshops Report

Description: The LCLS-II New Instruments workshops chaired by Phil Heimann and Jerry Hastings were held on March 19-22, 2012 at the SLAC National Accelerator Laboratory. The goal of the workshops was to identify the most exciting science and corresponding parameters which will help define the LCLS-II instrumentation. This report gives a synopsis of the proposed investigations and an account of the workshop. Scientists from around the world have provided short descriptions of the scientific opportunities they envision at LCLS-II. The workshops focused on four broadly defined science areas: biology, materials sciences, chemistry and atomic, molecular and optical physics (AMO). Below we summarize the identified science opportunities in the four areas. The frontiers of structural biology lie in solving the structures of large macromolecular biological systems. Most large protein assemblies are inherently difficult to crystallize due to their numerous degrees of freedom. Serial femtosecond protein nanocrystallography, using the 'diffraction-before-destruction' approach to outrun radiation damage has been very successfully pioneered at LCLS and diffraction patterns were obtained from some of the smallest protein crystals ever. The combination of femtosecond x-ray pulses of high intensity and nanosized protein crystals avoids the radiation damage encountered by conventional x-ray crystallography with focused beams and opens the door for atomic structure determinations of the previously largely inaccessible class of membrane proteins that are notoriously difficult to crystallize. The obtained structures will allow the identification of key protein functions and help in understanding the origin and control of diseases. Three dimensional coherent x-ray imaging at somewhat lower resolution may be used for larger objects such as viruses. The chemistry research areas of primary focus are the predictive understanding of catalytic mechanisms, with particular emphasis on photo- and heterogeneous catalysis. Of particular interest is the efficient conversion of light to electrical or chemical energy, which requires understanding the non-adiabatic ...
Date: August 8, 2012
Creator: Baradaran, Samira; Bergmann, Uwe; Durr, Herrmann; Gaffney, Kelley; Goldstein, Julia; Guehr, Markus et al.
Partner: UNT Libraries Government Documents Department

Images of Quark Intrinsic Motion in Covariant Parton Model

Description: We discuss the relations between TMDs and PDFs in the framework of the covariant parton model. The quark OAM and its connection to TMDs are studied as well.
Date: April 1, 2010
Creator: A.V. Efremov, P. Schweitzer, O.V. Teryaev, P. Zavada
Partner: UNT Libraries Government Documents Department

Spin and angular momentum in the nucleon

Description: Using the covariant spectator theory (CST), we present the results of a valence quark-diquark model calculation of the nucleon structure function f(x) measured in unpolarized deep inelastic scattering (DIS), and the structure functions g1(x) and g2(x) measured in DIS using polarized beams and targets. Parameters of the wave functions are adjusted to fit all the data. The fit fixes both the shape of the wave functions and the relative strength of each component. Two solutions are found that fit f(x) and g1(x), but only one of these gives a good description of g2(x). This fit requires the nucleon CST wave functions contain a large D-wave component (about 35%) and a small P-wave component (about 0.6%). The significance of these results is discussed.
Date: May 1, 2012
Creator: Franz Gross, Gilberto Ramalho, Teresa Pena
Partner: UNT Libraries Government Documents Department

EXACT FORM FOR SCATTERING AMPLITUDE IN REGGE POLE THEORY

Description: The exact form for the contribution of a single Regge pole is given both for positive and negative angular momentum without making the usual approximations. This exact form involves Legendre functions of the first and second kind with nonintegral index and argument greater than one. These functions are plotted. A one-parameter fit is made to the high-energy p-p elastic scattering data that give good agreement with experiment. (auth)
Date: September 1, 1963
Creator: Read, A.L.; Orear, J. & Bethe, H.A.
Partner: UNT Libraries Government Documents Department

Experimental status of high-spin states

Description: Changes occurring in high spin nuclear states are discussed. Experimental methods for studying reduction and eventual quenching of pairing interactions, changes in nuclear shapes, and alignment of individual particle angular momenta with increasing spin are reviewed. Emphasis is placed on the study of continuum gamma rays following heavy ion reactions. (12 figures) (SDF)
Date: September 1, 1975
Creator: Stephens, F.S.
Partner: UNT Libraries Government Documents Department

Continuum gamma rays following (HI, xn$gamma$) reactions

Description: The continuum gamma-ray spectrum following neutron emission in a (HI, xngamma) reaction consists of two parts: a high-energy component whose intensity decreases exponentially with gamma-energy, the initial statistical cascade; and a low-energy bump which usually contains most of the intensity and consists predominantly of stretched E2 transitions, the yrast cascade. The latter cascade carries away most of the angular momentum of the product nucleus, and so there is a good correlation between the average angular momentum of the initial compound nucleus leading to a particular product and the average gamma-ray multiplicity in that reaction. The measured values of the gamma-ray multiplicity show a variation of a factor of ten and have dependencies on the projectile mass and energy which can be explained with simple considerations. Determination of the moment-of-inertia of the nucleus at spins as high as 60h/2$pi$ involves difficulties and is not yet accurate, but is very interesting to do and seems possible of better accuracy. (1 table, 16 figures) (auth)
Date: August 1, 1975
Creator: Diamond, R.M.
Partner: UNT Libraries Government Documents Department

Global polarization measurement in Au+Au collisions

Description: The system created in non-central relativisticnucleus-nucleus collisions possesses large orbital angular momentum. Dueto spin-orbit coupling, particles produced in such a system could becomeglobally polarized along the direction of the system angular momentum. Wepresent the results of Lambda and anti-Lambda hyperon global polarizationmeasurements in Au+Au collisions at sqrt sNN=62.4 GeV and 200 GeVperformed with the STAR detector at RHIC. The observed globalpolarization of Lambda and anti-Lambda hyperons in the STAR acceptance isconsistent with zero within the precision of the measurements. Theobtained upper limit, lbar P Lambda, anti-Lambda rbar<= 0.02, iscompared to the theoretical values discussed recently in theliterature.
Date: August 2, 2007
Creator: Abelev, B.I.; Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett,J.; Anderson, B.D. et al.
Partner: UNT Libraries Government Documents Department

Global quark polarization in non-central A+A collisions

Description: Partons produced in the early stage of non-central heavy-ioncollisionscan develop a longitudinal fluid shear because of unequal localnumber densities of participant target and projectile nucleons. Undersuch fluid shear, local parton pairs with non-vanishing impact parameterhave finite local relative orbital angular momentum along the directionopposite to the reaction plane. Such finite relative orbitalangularmomentum among locally interacting quark pairs can lead to global quarkpolarization along the same direction due to spin-orbital coupling. Locallongitudinal fluid shear is estimated within both Landau fireball andBjorken scaling model of initial parton production. Quark polarizationthrough quark-quark scatterings with the exchange of a thermal gluon iscalculated beyond small-angle scattering approximation in a quark-gluonplasma. The polarization is shown to have a non-monotonic dependence onthe local relative orbital angular momentum dictated by the interplaybetween electric and magnetic interaction. It peaks at a value ofrelative orbital angular momentum which scales with the magnetic mass ofthe exchanged gluons. With the estimated small longitudinal fluid shearin semi-peripheral Au+Au collisions at the RHIC energy, the final quarkpolarization is found to be small left hbar P_q right hbar<0.04 inthe weak coupling limit. Possible behavior of the quark polarization inthe strong coupling limit and implications on the experimental detectionof such global quark polarization at RHIC and LHC are alsodiscussed.
Date: October 12, 2007
Creator: Gao, Jian-Hua; Chen, Shou-Wan; Deng, Wei-tian; Tang, Zuo-Tang; Wang, Qun & Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department

A hybridGaussian-discrete variable representation approach to molecular continuum processes II: application to photoionization of diatomic Li2+

Description: We describe an approach for studying molecular photoionization with a hybrid basis that combines the functionality of analytic basis sets to represent electronic coordinates near the nuclei of a molecule with numerically-defined grid-based functions. We discuss the evaluation of the various classes of two-electron integrals that occur in a hybrid basis consisting of Gaussian type orbitals (GTOs) and discrete variable representation (DVR) functions. This combined basis is applied to calculate single photoionization cross sections for molecular Li_2+, which has a large equilibrium bond distance (R=5.86a_0). The highly non-spherical nature of Li_2+ molecules causes higher angular momentum components to contribute significantly to the cross section even at low photoelectron energies, resulting in angular distributions that appear to be f-wave dominated near the photoionization threshold. At higher energies, where the de Broglie wavelength of the photoelectron becomes comparable with the bond distance, interference effects appear in the photoionization cross section. These interference phenomena appear at much lower energies than would be expected for diatomic targets with shorter internuclear separations.
Date: August 1, 2008
Creator: Rescigno, Thomas N; Yip, Frank L.; McCurdy, C. William & Rescigno, Thomas N.
Partner: UNT Libraries Government Documents Department

PARTON DISTRIBUTIONS AND SPIN-ORBITAL CORRELATIONS.

Description: In this talk, the author summarizes a recent study showing that the large-x parton distributions contain important information on the quark orbital angular momentum of nucleon. This contribution could explain the conflict between the experimental data and the theory predictions for the polarized quark distributions. Future experiments at JLAB shall provide further test for our predictions.
Date: May 21, 2007
Creator: FENG,Y.
Partner: UNT Libraries Government Documents Department

EMITTANCE COMPENSATION FOR MAGNETIZED BEAMS

Description: Emittance compensation is a well established technique for minimizing the emittance of an electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincide the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating game. We describe a method and tools for a compensation that includes the beam magnetization.
Date: June 25, 2007
Creator: KEWISCH,J. & CHANG, X.
Partner: UNT Libraries Government Documents Department

Element-specific spin and orbital momentum dynamics of Fe/Gdmultilayers

Description: The role of orbital magnetism in the laser-induced demagnetization of Fe/Gd multilayers was investigated using time-resolved X-ray magnetic circular dichroism at 2-ps time resolution given by an x-ray streak camera. An ultrafast transfer of angular momentum from the spin via the orbital momentum to the lattice was observed which was characterized by rapidly thermalizing spin and orbital momenta. Strong interlayer exchange coupling between Fe and Gd led to a simultaneous demagnetization of both layers.
Date: March 23, 2007
Creator: Bartelt, A.F.; Comin, A.; Feng, J.; Nasiatka, J.R.; Eimuller, T.; Ludescher, B. et al.
Partner: UNT Libraries Government Documents Department

THE RISE AND FALL OF THE SPIN ALIGNMENT IN DEEP-INELASTIC REACTIONS

Description: Both the magnitude and alignment of the transferred angular momentum in the reaction {sup 165}Ho + {sup 165}Ho have been measured as a function of Q value via continuum {gamma}-ray multiplicity and anisotropy techniques. Two regimes are observed: A low-Q-value regime where the aligned angular momentum component dominates over the random components, and a large-Q-value regime where the random components dominate and decrease the spin alignment.
Date: July 1, 1980
Creator: Wozniak, G.J.; McDonald, R.J.; Pacheco, A.J.; Hsu, C.C.; Morrissey, D.J.; Sobotka, L.G. et al.
Partner: UNT Libraries Government Documents Department

Emergence of the Persistent Spin Helix in Semiconductor Quantum Wells

Description: According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit (SO) coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be recovered in a two-dimensional electron gas (2DEG), despite the presence of SO coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix' (PSH). SU(2) is restored, in principle, when the strength of two dominant SO interactions, the Rashba ({alpha}) and linear Dresselhaus ({beta}{sub 1}), are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term ({beta}{sub 3}) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as {alpha} {yields} {beta}{sub 1}. Here we observe experimentally the emergence of the PSH in GaAs quantum wells (QW's) by independently tuning {alpha} and {beta}{sub 1}. Using transient spin-grating spectroscopy (TSG), we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant SO terms, identifying {beta}{sub 3} as the main SU(2) violating term in our samples. The tunable suppression of spin-relaxation demonstrated in this work is well-suited for application to spintronics.
Date: August 24, 2011
Creator: Koralek, Jake; Weber, Chris; Orenstein, Joe; Bernevig, Andrei; Zhang, Shoucheng; Mack, Shawn et al.
Partner: UNT Libraries Government Documents Department

NUCLEAR SHAPES AT HIGH ANGULAR MOMENTUM

Description: Multiplicities as a function of {gamma}-ray energy have been measured for continuum {gamma}-ray spectra produced in argon- and calcium-induced reactions. A peak sometimes occurs in the multiplicity spectrum, indicating a correlation between {gamma}-ray energy and multiplicity (spin). This correlation can be explained by rotational motion of the nucleus, suggesting basically prolate nuclear shapes. Absence of structure in the multiplicity spectrum is interpreted to indicate non-collective motion, and hence spherical or oblate shapes.
Date: December 1, 1977
Creator: Deleplanque, M.A.; Lee, I.Y.; Stephens, F.S.; Diamond, R.M. & Aleonard, M.M.
Partner: UNT Libraries Government Documents Department

Observation of Spin Coulomb Drag in a Two-Dimensional Electron Gas

Description: An electron propagating through a solid carries spin angular momentum in addition to its mass and charge. Of late there has been considerable interest in developing electronic devices based on the transport of spin, which offer potential advantages in dissipation, size, and speed over charge-based devices. However, these advantages bring with them additional complexity. Because each electron carries a single, fixed value (-e) of charge, the electrical current carried by a gas of electrons is simply proportional to its total momentum. A fundamental consequence is that the charge current is not affected by interactions that conserve total momentum, notably collisions among the electrons themselves. In contrast, the electron's spin along a given spatial direction can take on two values, {+-} {h_bar}/2 (conventionally {up_arrow}, {down_arrow}), so that the spin current and momentum need not be proportional. Although the transport of spin polarization is not protected by momentum conservation, it has been widely assumed that, like the charge current, spin current is unaffected by electron-electron (e-e) interactions. Here we demonstrate experimentally not only that this assumption is invalid, but that over a broad range of temperature and electron density, the flow of spin polarization in a two-dimensional gas of electrons is controlled by the rate of e-e collisions.
Date: August 19, 2011
Creator: Weber, C.P.
Partner: UNT Libraries Government Documents Department

Observation of Exclusive Dijet Production at the Fermilab Tevatron p-pbar Collider

Description: The authors present the first observation and cross section measurement of exclusive dijet production in {bar p}p interactions, {bar p}p {yields} {bar p} + dijet + p. Using a data sample of 310 pb{sup -1} collected by the Run II Collider Detector at Fermilab at {radical}s = 1.96 TeV, exclusive cross sections for events with two jets of transverse energy E{sub T}{sup jet} {ge} 10 GeV have been measured as a function of minimum E{sub T}{sup jet}. The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200 pb{sup -1} of b-tagged jet events, where exclusive dijet production is expected to be suppressed by the J{sub z} = 0 total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the pp Large Hadron Collider at {radical}s = 14 TeV are discussed.
Date: December 1, 2007
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Adelman, J.; /Chicago U., EFI; Akimoto, T.; U., /Tsukuba et al.
Partner: UNT Libraries Government Documents Department

On the Nature of Ultraluminous X-Ray Sources, Or What a Black Hole Should Look Like

Description: We derive the luminosity-temperature relation for the accreting black holes (BHs). At the accretion rates below the critical Eddington, the BHs are described by the standard Shakura-Sunyaev model resulting in the L {infinity} T{sup 4} {infinity} M relation. At super-Eddington rates, {dot m} = {dot M}/{dot M}{sub Edd} &gt;&gt; 1, a strong outflow forms within the spherization radius R{sub sp} {infinity} {dot M}. If the angular momentum of the outflowing matter is conserved and typical outflow velocities are of the order of Keplerian, the wind occupies 50-85 per cent of the sky as viewed from the BH, while the region around the rotation axis remains transparent. The bolometric luminosity in such a case is known to exceed the Eddington luminosity by a factor 1 + ln {dot m} and the observed luminosity is 2-7 times higher because of geometrical beaming. An edge-on observer sees only the soft emission from the extended envelope, with the photosphere radius exceeding R{sub sp} by orders of magnitude. The photosphere temperature follows the T{sub ph} {infinity} {dot M}{sup -3/4} or {dot M}{sup -1} relation depending on the velocity profile at R &gt; R{sub sp} (constant velocity or a Keplerian profile). The resulting L-T{sub ph} dependence is consistent with that observed in the super-Eddington accreting BHs SS 433 and V4641 Sgr. A face-on observer has a direct view of the inner hot accretion disc which in stellar-mass BHs has temperature T{sub max} of a few keV. The effective temperature depends on radius as {infinity} R{sup -1/2} (up to the spherization radius) and the emitted spectrum is a power-law F{sub E} {infinity} E{sup -1} extending from {approx} 3T{sub max} down to the temperature at the spherization radius T{sub sp} {approx} {dot m}{sup -1/2} keV. It continues further as a power-law F{sub E} {infinity} E{sup 1/3} to the ...
Date: September 18, 2006
Creator: Poutanen, Juri; /Oulu U. /KIPAC, Menlo Park; Fabrika, Sergei; /Stavropol, Astrophys. Observ.; Butkevich, Alexey G.; /Oulu U. /Pulkovo Observ., St. Petersburg et al.
Partner: UNT Libraries Government Documents Department

Formation of Primordial Stars in a Lambda-CDM Universe

Description: Primordial stars are formed from a chemically pristine gas consisting of hydrogen and helium. They are believed to have been born at some early epoch in the history of the Universe and to have enriched the interstellar medium with synthesized heavy elements before the emergence of ordinary stellar populations. We study the formation of the first generation of stars in the standard cold dark matter model. We follow the gravitational collapse and thermal evolution of primordial gas clouds within early cosmic structures using very high-resolution, cosmological hydrodynamic simulations. Our simulation achieves a dynamic range of {approx} 10{sup 10} in length scale. With accurate treatment of atomic and molecular physics, it allows us to study the chemo-thermal evolution of primordial gas clouds to densities up to {rho} {approx} 2 x 10{sup -8}g cm{sup -3} (n{sub H} {approx} 10{sup 16}cm{sup -3}) without assuming any a priori equation of state; a six orders of magnitudes improvement over previous three-dimensional calculations. We implement an extensive chemistry network for hydrogen, helium and deuterium. All the relevant atomic and molecular cooling and heating processes, including cooling by collision-induced continuum emission, are implemented. For calculating optically thick H{sub 2} cooling at high densities, we use the Sobolev method (Sobolev 1960) and evaluate the molecular line opacities for a few hundred lines. We validate the accuracy of the method by performing a spherical collapse test and comparing the results with those of accurate one-dimensional calculations that treat the line radiative transfer problem in a fully self-consistent manner. We then perform a cosmological simulation adopting the standard {Lambda}CDM model. Dense gas clumps are formed at the centers of low mass ({approx} 10{sup 5-6}M{sub {circle_dot}}) dark matter halos at redshifts z {approx} 20, and they collapse gravitationally when the cloud mass exceeds a few hundred solar masses. To examine possible ...
Date: June 9, 2006
Creator: Yoshida, Naoki; U., /Nagoya; Omukai, Kazuyuki; /Tokyo, Astron. Observ.; Hernquist, Lars; Astrophys., /Harvard-Smithsonian Ctr. et al.
Partner: UNT Libraries Government Documents Department

Emergence of Strong Exchange Interaction in the Actinide Series: The Driving Force for Magnetic Stabilization of Curium

Description: Using electron energy-loss spectroscopy in a transmission electron microscope, many-electron atomic spectral calculations and density functional theory, we examine the electronic and magnetic structure of Cm metal. We show that angular momentum coupling in the 5f states plays a decisive role in the formation of the magnetic moment. The 5f states of Cm in intermediate coupling are strongly shifted towards the LS coupling limit due to exchange interaction, unlike most actinide elements where the effective spin-orbit interaction prevails. It is this LS-inclined intermediate coupling that is the key to producing the large spin polarization which in turn dictates the newly found crystal structure of Cm under pressure.
Date: January 4, 2007
Creator: Moore, K; der Laan, G v; Haire, D; Wall, M; Schwartz, A & Soderlind, P
Partner: UNT Libraries Government Documents Department

Hadron Spectroscopy and Wavefunctions in QCD and the AdS/CFT Correspondence

Description: The AdS/CFT correspondence has led to important insights into the properties of quantum chromodynamics even though QCD is a broken conformal theory. We have recently shown how a holographic model based on a truncated AdS space can be used to obtain the hadronic spectrum of light q{bar q}, qqq and gg bound states. Specific hadrons are identified by the correspondence of string modes with the dimension of the interpolating operator of the hadron's valence Fock state, including orbital angular momentum excitations. The predicted mass spectrum is linear M {proportional_to} L at high orbital angular momentum, in contrast to the quadratic dependence M{sup 2} {proportional_to} L found in the description of spinning strings. Since only one parameter, the QCD scale LQCD, is introduced, the agreement with the pattern of physical states is remarkable. In particular, the ratio of D to nucleon trajectories is determined by the ratio of zeros of Bessel functions. The light-front quantization of gauge theories in light-cone gauge provides a frame-independent wavefunction representation of relativistic bound states, simple forms for current matrix elements, explicit unitarity, and a trivial vacuum. The light-front Fock-state wavefunctions encode the bound state properties of hadrons in terms of their quark and gluon degrees of freedom at the amplitude level. One can also use the extended AdS/CFT space-time theory to obtain a model for hadronic light-front wavefunctions, thus providing a relativistic description of hadrons in QCD at the amplitude level. The model wavefunctions display confinement at large inter-quark separation and conformal symmetry at short distances. In particular, the scaling and conformal properties of the LFWFs at high relative momenta agree with perturbative QCD. These AdS/CFT model wavefunctions could be used as an initial ansatz for a variational treatment of the light-front QCD Hamiltonian. We also show how hadron form factors in both the space-like ...
Date: October 13, 2005
Creator: Brodsky, Stanley J.; de Teramond, Guy F. & U., /SLAC /Costa Rica
Partner: UNT Libraries Government Documents Department

Gauge/Gravity Duality and Strongly Coupled Light-Front Dynamics

Description: We find a correspondence between semiclassical gauge theories quantized on the light-front and a dual gravity model in anti-de Sitter (AdS) space, thus providing an initial approximation to QCD in its strongly coupled regime. This correspondence - light-front holography - leads to a light-front Hamiltonian and relativistic bound-state wave equations in terms of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. Light-front holography also allows a precise mapping of transition amplitudes from AdS to physical space-time. In contrast with the usual AdS/QCD framework, the internal structure of hadrons is explicitly introduced in the gauge/gravity correspondence and the angular momentum of the constituents plays a key role. We also discuss how to introduce higher Fock-states in the correspondence as well as their relevance for describing the detailed structure of space and time-like form factors.
Date: August 12, 2011
Creator: de Teramond, Guy F.; U., /Costa Rica; Brodsky, Stanley J. & /SLAC /Southern Denmark U., CP3-Origins
Partner: UNT Libraries Government Documents Department

Light-Front Holography and Novel Effects in QCD

Description: The correspondence between theories in anti-de Sitter space and conformal field theories in physical space-time leads to an analytic, semiclassical model for strongly-coupled QCD. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time, thus providing a relativistic description of hadrons at the amplitude level. We identify the AdS coordinate z with an invariant light-front coordinate {zeta} which separates the dynamics of quark and gluon binding from the kinematics of constituent spin and internal orbital angular momentum. The result is a single-variable light-front Schroedinger equation for QCD which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The mapping of electromagnetic and gravitational form factors in AdS space to their corresponding expressions in light-front theory confirms this correspondence. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates and the behavior of the QCD coupling in the infrared. The distinction between static structure functions such as the probability distributions computed from the square of the light-front wavefunctions versus dynamical structure functions which include the effects of rescattering is emphasized. A new method for computing the hadronization of quark and gluon jets at the amplitude level, an event amplitude generator, is outlined.
Date: December 18, 2008
Creator: Brodsky, Stanley J. & de Teramond, Guy F.
Partner: UNT Libraries Government Documents Department

Light-Front Holography, Light-Front Wavefunctions, and Novel QCD Phenomena

Description: Light-Front Holography is one of the most remarkable features of the AdS/CFT correspondence. In spite of its present limitations it provides important physical insights into the nonperturbative regime of QCD and its transition to the perturbative domain. This novel framework allows hadronic amplitudes in a higher dimensional anti-de Sitter (AdS) space to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The model leads to an effective confining light-front QCD Hamiltonian and a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound-state wavefunctions, and thus the fall-off as a function of the invariant mass of the constituents. The soft-wall holographic model modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics - a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryons. The model predicts a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number n. The hadron eigensolutions projected on the free Fock basis provides the complete set of valence and non-valence light-front Fock state wavefunctions {Psi}{sub n/H} (x{sub i}, k{sub {perpendicular}i}, {lambda}{sub i}) which describe the hadron's momentum and spin distributions needed to compute the direct measures of hadron structure at the quark and gluon level, such as elastic and transition form factors, distribution amplitudes, structure functions, generalized parton distributions and transverse momentum distributions. The effective confining potential also creates quark-antiquark pairs from the amplitude q {yields} q{bar q}q. Thus in holographic QCD ...
Date: February 16, 2012
Creator: Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins; de Teramond, Guy F. & U., /Costa Rica
Partner: UNT Libraries Government Documents Department