Publications (89)178.58 Total impact
 [Show abstract] [Hide abstract]
ABSTRACT: A primary question in hadron physics is how the mass scale for hadrons consisting of light quarks, such as the proton, emerges from the QCD Lagrangian even in the limit of zero quark mass. If one requires the effective action which underlies the QCD Lagrangian to remain conformally invariant and extends the formalism of de Alfaro, Fubini and Furlan to lightfront Hamiltonian theory, then a unique, colorconfining potential with a mass parameter $\kappa$ emerges. The actual value of the parameter $\kappa$ is not set by the model  only ratios of hadron masses and other hadronic mass scales are predicted. The result is a nonperturbative, relativistic lightfront quantum mechanical wave equation, the LightFront Schr\"odinger Equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the identical slope in the radial quantum number $n$ and orbital angular momentum $L$. The same lightfront equations for mesons with spin $J$ also can be derived from the holographic mapping to QCD (3+1) at fixed lightfront time from the softwall model modification of AdS$_5$ space with a specific dilaton profile. Lightfront holography thus provides a precise relation between the boundstate amplitudes in the fifth dimension of AdS space and the boostinvariant lightfront wavefunctions describing the internal structure of hadrons in physical spacetime. One can also extend the analysis to baryons using superconformal algebra  $2 \times 2$ supersymmetric representations of the conformal group. The resulting fermionic LF boundstate equations predict striking similarities between the meson and baryon spectra. In fact, the holographic QCD lightfront Hamiltonians for the states on the meson and baryon trajectories are identical if one shifts the internal angular...  [Show abstract] [Hide abstract]
ABSTRACT: Establishing an explicit connection between the long distance physics of confinement and the dynamical interactions of quarks and gluons at short distances has been a longsought goal of quantum chromodynamics. Using holographic QCD, we derive a direct analytic relation between the scale $\kappa$ which determines the masses of hadrons and the scale $\Lambda_{s}$ which controls the predictions of perturbative QCD at very short distances. The resulting prediction $\Lambda_{s}=0.341\pm0.032$ GeV in the $\overline{MS}$ scheme agrees well with the experimental average $0.339\pm0.016$ GeV. We also derive a relation between $\Lambda_{s}$ and the QCD string tension $\sigma$. This connection between the fundamental hadronic scale underlying the physics of quark confinement and the perturbative QCD scale controlling hard collisions can be carried out in any renormalization scheme.  [Show abstract] [Hide abstract]
ABSTRACT: QCD is well understood at short distances where perturbative calculations are feasible. Establishing an explicit analytic connection between the shortdistance regime and the largedistance physics of quark confinement has been a longsought goal. A major challenge is to relate the scale $\Lambda_{s}$ underlying the evolution of the QCD coupling in the perturbative regime to the masses of hadrons. We show here how new theoretical insights into the behavior of QCD at large distances leads to such a relation. The resulting prediction for $\Lambda_{s}$ in the $\overline{MS}$ scheme agrees well with experimental measurements. Conversely, the relation can be used to predict the masses of hadrons composed of light quarks with the measured value of $\Lambda_{s}$ as the sole parameter. We also use "lightfront holography" to determine the analytic form of $\alpha_s(Q^2)$ at small $Q^2$.  [Show abstract] [Hide abstract]
ABSTRACT: Relativistic lightfront boundstate equations for mesons and baryons can be constructed in the chiral limit from the supercharges of a superconformal algebra which connect baryon and meson spectra. Quark masses break the conformal invariance, but the basic underlying supersymmetric mechanism, which transforms meson and baryon wave functions into each other, still holds and gives remarkable connections across the entire spectrum of light and heavylight hadrons. We also briefly examine the consequences of extending the superconformal relations to doubleheavy mesons and baryons.  [Show abstract] [Hide abstract]
ABSTRACT: The valence Fockstate wavefunctions of the lightfront (LF) QCD Hamiltonian satisfy a relativistic equation of motion, analogous to the nonrelativistic radial Schrödinger equation, with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. If one requires that the effective action which underlies the QCD Lagrangian remains conformally invariant and extends the formalism of de Alfaro, Fubini and Furlan to LF Hamiltonian theory, the potential U has a unique form of a harmonic oscillator potential, and a mass gap arises. The result is a nonperturbative relativistic LF quantum mechanical wave equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number n and orbital angular momentum L. Only one mass parameter κ appears. The corresponding LF Dirac equation provides a dynamical and spectroscopic model of nucleons. The same LF equations arise from the holographic mapping of the softwall model modification of AdS5 space with a unique dilaton profile to QCD (3+1) at fixed LF time. LF holography thus provides a precise relation between the boundstate amplitudes in the fifth dimension of Antide Sitter (AdS) space and the boostinvariant LFWFs describing the internal structure of hadrons in physical spacetime. We also show how the mass scale \({\kappa= m_\rho/\sqrt{2}}\) underlying confinement and the masses of lightquark hadrons determines the scale \({\Lambda_{\overline{MS}}^{(N_F=3)}}\) controlling the evolution of the perturbative QCD coupling. The relation between scales is obtained by matching the nonperturbative dynamics, as described by an effective conformal theory mapped to the LF and its embedding in AdS space, to the perturbative QCD regime computed to fourloop order. The data for the effective coupling defined from the Bjorken sum rule \({\alpha_{g_1}(Q^2)}\) are remarkably consistent with the Gaussian form predicted by LF holographic QCD. The result is an effective coupling defined at all momenta. The predicted value \({\Lambda^{(N_F=3)}_{\overline{MS}} = 0.423 m_\rho = 0.328 \pm 0.034}\) GeV is in agreement with the world average \({0.339 \pm 0.010}\) GeV. We thus can connect \({\Lambda_{\overline{MS}}^{(N_F=3)}}\) to hadron masses. The analysis applies to any renormalization scheme.  [Show abstract] [Hide abstract]
ABSTRACT: We construct an effective QCD lightfront Hamiltonian for both mesons and baryons in the chiral limit based on the generalized supercharges of a superconformal graded algebra. The superconformal construction is shown to be equivalent to a semiclassical approximation to lightfront QCD and its embedding in AdS space. The specific breaking of conformal invariance inside the graded algebra uniquely determines the effective confinement potential. The generalized supercharges connect the baryon and meson spectra to each other in a remarkable manner. In particular, the $\pi/b_1$ Regge trajectory is identified as the superpartner of the nucleon trajectory. However, the lowestlying state on this trajectory, the $\pi$meson is massless in the chiral limit and has no supersymmetric partner. 
Article: Baryon Spectrum from Superconformal Quantum Mechanics and its LightFront Holographic Embedding
[Show abstract] [Hide abstract]
ABSTRACT: We describe the observed lightbaryon spectrum by extending superconformal quantum mechanics to the light front and its embedding in AdS space. This procedure uniquely determines the confinement potential for arbitrary halfinteger spin. To this end, we show that fermionic wave equations in AdS space are dual to lightfront supersymmetric quantum mechanical boundstate equations in physical spacetime. The specific breaking of conformal invariance inside the algebra explains hadronic properties common to light mesons and baryons, such as the observed mass pattern in the radial and orbital excitations. The holographic embedding in AdS also explains distinctive and systematic features, such as the spinJ degeneracy observed in the light baryon spectrum.  [Show abstract] [Hide abstract]
ABSTRACT: The valence Fockstate wavefunctions of the lightfront QCD Hamiltonian satisfy a relativistic equation of motion with an effective confining potential $U$ which systematically incorporates the effects of higher quark and gluon Fock states. If one requires that the effective action which underlies the QCD Lagrangian remains conformally invariant and extends the formalism of de Alfaro, Fubini and Furlan to light front Hamiltonian theory, the potential $U$ has a unique form of a harmonic oscillator potential, and a mass gap arises. The result is a nonperturbative relativistic lightfront quantum mechanical wave equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number $n$ and orbital angular momentum $L$. Only one mass parameter $\kappa$ appears. Lightfront holography thus provides a precise relation between the boundstate amplitudes in the fifth dimension of AdS space and the boostinvariant lightfront wavefunctions describing the internal structure of hadrons in physical spacetime. We also show how the mass scale $\kappa$ underlying confinement and hadron masses determines the scale $\Lambda_{\overline{MS}} $ controlling the evolution of the perturbative QCD coupling. The relation between scales is obtained by matching the nonperturbative dynamics, as described by an effective conformal theory mapped to the lightfront and its embedding in AdS space, to the perturbative QCD regime computed to fourloop order. The result is an effective coupling defined at all momenta. The predicted value $\Lambda_{\overline{MS}} = 0.328 \pm 0.034$ GeV is in agreement with the world average $0.339 \pm 0.010$ GeV. The analysis applies to any renormalization scheme.  [Show abstract] [Hide abstract]
ABSTRACT: We show how the physical mass scale $\kappa$ underlying confinement and hadron masses determines the scale $\Lambda_s$ in the QCD running coupling. The relation between scales is obtained by matching the nonperturbative dynamics, as described by an effective conformal theory mapped to the lightfront and its embedding in AdS space, to the perturbative QCD regime computed to fourloop order. The result is an effective coupling defined at all momenta. The predicted value $\Lambda_{\overline{MS}} = 0.328 \pm 0.034$ GeV is in agreement with the world average $0.339 \pm 0.010$ GeV. Our analysis applies to any renormalization scheme.  [Show abstract] [Hide abstract]
ABSTRACT: In this Report we explore the remarkable connections between lightfront dynamics, its holographic mapping to gravity in a higherdimensional antide Sitter (AdS) space, and conformal quantum mechanics. This approach provides new insights into the origin of a fundamental mass scale and the physics underlying confinement dynamics in QCD in the limit of massless quarks. The result is a relativistic lightfront wave equation for arbitrary spin with an effective confinement potential derived from a conformal action and its embedding in AdS space. This equation allows for the computation of essential features of hadron spectra in terms of a single scale. The lightfront holographic methods described here gives a precise interpretation of holographic variables and quantities in AdS space in terms of lightfront variables and quantum numbers. This leads to a relation between the AdS wave functions and the boostinvariant lightfront wavefunctions describing the internal structure of hadronic boundstates in physical spacetime. The pion is massless and the excitation spectra of relativistic lightquark meson and baryon bound states lie on linear Regge trajectories with identical slopes in the radial and orbital quantum numbers. In the lightfront holographic approach described here currents are expressed as an infinite sum of poles, and form factors as a product of poles. At large $q^2$ the form factor incorporates the correct powerlaw falloff for hard scattering independent of the specific dynamics and is dictated by the twist. At low $q^2$ the form factor leads to vector dominance. The approach is also extended to include small quark masses. We briefly review in this Report other holographic approaches to QCD, in particular topdown and bottomup models based on chiral symmetry breaking. We also include a discussion of open problems and future applications.  [Show abstract] [Hide abstract]
ABSTRACT: We describe a procedure to extend the lightfront holographic approach to hadronic physics to include lightquark masses. The proposed framework allows us to extend the formalism of de Alfaro, Fubini and Furlan to the frameindependent lightfront Hamiltonian theory in the approximation where the dynamics in the invariant transverse variable is unchanged to first order in the quark masses. The confinement potential follows from an effective theory which encodes the fundamental conformality of the classical QCD Lagrangian and leads to a semiclassical relativistic lightfront wave equation for arbitrary spin. In particular, the K meson spectrum is successfully described without modifying the emerging confinement scale. The Wilson loop criteria for confinement is maintained, since for light quark masses a harmonic potential and linear Regge trajectories in the lightfront form of dynamics corresponds to a linear potential in the usual instantform.  [Show abstract] [Hide abstract]
ABSTRACT: We describe a procedure to extend the lightfront holographic approach to hadronic physics to include lightquark masses. The proposed framework allows us to extend the formalism of de Alfaro, Fubini and Furlan to the frameindependent lightfront Hamiltonian theory in the approximation where the dynamics in the invariant transverse variable is unchanged to first order in the quark masses. The confinement potential follows from an effective theory which encodes the fundamental conformality of the classical QCD Lagrangian and leads to a semiclassical relativistic lightfront wave equation for arbitrary spin. In particular, the K meson spectrum is successfully described without modifying the emerging confinement scale. The Wilson loop criteria for confinement is maintained, since for light quark masses a harmonic potential and linear Regge trajectories in the lightfront form of dynamics corresponds to a linear potential in the usual instantform.  [Show abstract] [Hide abstract]
ABSTRACT: One of the most fundamental problems in Quantum Chromodynamics is to understand the origin of the mass scale which controls the range of color confinement and the hadronic spectrum. We show that a mass gap and a fundamental color confinement scale arise when one extends the formalism of de Alfaro, Fubini and Furlan to frameindependent lightfront Hamiltonian theory. Remarkably, the resulting lightfront potential has a unique form of a harmonic oscillator in the lightfront invariant impact variable if one requires that the action remains conformally invariant. The result is a singlevariable relativistic equation of motion for $q \bar q$ bound states, a "LightFront Shr\"odinger Equation", analogous to the nonrelativistic radial Schr\"odinger equation, which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number and orbital angular momentum. The same equations with the correct hadron spin dependence arise from the holographic mapping of modified AdS$_5$ space with a specific dilaton profile. A fundamental mass parameter $\kappa$ appears, determining the hadron masses and the length scale which underlies hadron structure. Quark masses can be introduced to account for the spectrum of strange hadrons. This LightFront Holographic approach predicts not only hadron spectroscopy successfully, but also hadronic form factors, the QCD running coupling at small virtuality, and the lightfront wavefunctions of hadrons. Thus the combination of lightfront dynamics, its holographic mapping to gravity in a higherdimensional space and the dAFF procedure provides new insight into the physics underlying color confinement, chiral invariance, and the QCD mass scale.  [Show abstract] [Hide abstract]
ABSTRACT: We observe that the effective potentials obtained from lattice gauge theory, derived from string models of hadrons, and determined from models using frontform dynamics and lightfront holography agree with each other at leading approximation, not only in their shape  which depends on the form of dynamics  but also in their numerical strength.  [Show abstract] [Hide abstract]
ABSTRACT: We briefly review the remarkable connections between lightfront QCD, gravity in AdS space, and conformal quantum mechanics. We discuss, in particular, the group theoretical and geometrical aspects of the underlying onedimensional quantum field theory. The resulting effective theory leads to a phenomenologically successful confining interaction potential in the relativistic lightfront wave equation which incorporates relevant nonperturbative dynamical aspects of hadron physics.  [Show abstract] [Hide abstract]
ABSTRACT: To a first semiclassical approximation one can reduce the multiparton lightfront problem in QCD to an effective onedimensional quantum field theory, which encodes the fundamental conformal symmetry of the classical QCD Lagrangian. This procedure leads to a relativistic lightfront wave equation for arbitrary spin which incorporates essential spectroscopic and nonperturbative dynamical features of hadron physics. The mass scale for confinement and higher dimensional holographic mapping to AdS space are also emergent properties of this framework.  [Show abstract] [Hide abstract]
ABSTRACT: Lightfront Hamiltonian theory, derived from the quantization of the QCD Lagrangian at fixed lightfront time x + = x 0 + x 3, provides a rigorous frameindependent framework for solving nonperturbative QCD. The eigenvalues of the lightfront QCD Hamiltonian H LF predict the hadronic mass spectrum, and the corresponding eigensolutions provide the lightfront wavefunctions which describe hadron structure, providing a direct connection to the QCD Lagrangian. In the semiclassical approximation the valence Fockstate wavefunctions of the lightfront QCD Hamiltonian satisfy a singlevariable relativistic equation of motion, analogous to the nonrelativistic radial Schrödinger equation, with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. Remarkably, the potential U has a unique form of a harmonic oscillator potential if one requires that the chiral QCD action remains conformally invariant. A mass gap and the color confinement scale also arises when one extends the formalism of de Alfaro, Fubini and Furlan to lightfront Hamiltonian theory. In the case of mesons, the valence Fockstate wavefunctions of H LF for zero quark mass satisfy a singlevariable relativistic equation of motion in the invariant variable \({\zeta^2=b^2_\perp x(1x)}\), which is conjugate to the invariant mass squared \({{M^2_{q\bar q}}}\). The result is a nonperturbative relativistic lightfront quantum mechanical wave equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories \({M^2(n, L, S) = 4\kappa^2( n+L +S/2)}\) with the same slope in the radial quantum number n and orbital angular momentum L. Only one mass parameter \({\kappa}\) appears. The corresponding lightfront Dirac equation provides a dynamical and spectroscopic model of nucleons. The same lightfront equations arise from the holographic mapping of the softwall model modification of AdS5 space with a unique dilaton profile to QCD (3 + 1) at fixed lightfront time. Lightfront holography thus provides a precise relation between the boundstate amplitudes in the fifth dimension of AdS space and the boostinvariant lightfront wavefunctions describing the internal structure of hadrons in physical spacetime. We also discuss the implications of the underlying conformal template of QCD for renormalization scalesetting and the implications of lightfront quantization for the value of the cosmological constant.  [Show abstract] [Hide abstract]
ABSTRACT: Antide Sitter space in five dimensions provides an exact geometrical representation of the conformal group. Remarkably, gravity in AdS$_5$ space is holographically dual to frameindependent lightfront Hamiltonian theory, derived from the quantization of the QCD Lagrangian at fixed lightfront time $\tau = x^0+x^3$. Lightfront holography also leads to a precise relation between the boundstate amplitudes in the fifth dimension $z$ of AdS space and the variable $\zeta$, where $\zeta^2 = b^2_\perp x(1x)$ is the argument of the boostinvariant lightfront wavefunctions describing the internal structure of hadrons in physical spacetime. The holographic mapping of AdS space with a specific "softwall" dilaton yields a confining potential $U(\zeta^2)$ for the lightfront Schr\"odinger equation for hadrons with arbitrary spin $J$. Remarkably, $U(\zeta^2)$ has a unique form of a harmonic oscillator potential if one requires that the chiral QCD action remains conformally invariant. One thus obtains an effective lightfront effective theory for general spin which respects the conformal symmetry of the fourdimensional classical QCD Lagrangian. The predictions of the LF equations of motion include a zeromass pion in the chiral $m_q\to 0$ limit, and linear Regge trajectories $M^2(n,L) \propto n+L$ with the same slope in the radial quantum number $n$ and the orbital angular momentum $L$. The lightfront AdS/QCD holographic approach gives a frameindependent representation of colorconfining dynamics, Regge spectroscopy, as well as the excitation spectra of relativistic lightquark meson and baryon bound states in QCD in terms of a single mass parameter. We also briefly discuss the implications of the underlying conformal template of QCD for renormalization scalesetting, and the implications of lightfront quantization for the value of the cosmological constant.  [Show abstract] [Hide abstract]
ABSTRACT: LightFront Hamiltonian theory, derived from the quantization of the QCD Lagrangian at fixed lightfront time \tau = t+z/c, provides a rigorous frameindependent framework for solving nonperturbative QCD. The eigenvalues of the lightfront QCD Hamiltonian predict the hadronic mass spectrum, and the eigensolutions provide the lightfront wavefunctions describing hadron structure. The valence Fockstate wavefunctions of the lightfront QCD Hamiltonian satisfy a singlevariable relativistic equation of motion, analogous to the nonrelativistic radial Schrodinger equation, with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. The potential U has a unique form if one requires that the action for zero quark mass remains conformally invariant. The holographic mapping of gravity in AdS space to QCD with a specific softwall dilaton yields the same lightfront Schrodinger equation. It also gives a precise relation between the boundstate amplitudes in the fifth dimension z of AdS space and the boostinvariant lightfront wavefunctions describing the internal structure of hadrons in physical spacetime. The elastic and transition form factors of the pion and the nucleons are found to be well described in this framework. The predictions include a zeromass pion in the chiral limit, and linear Regge trajectories with the same slope in the radial quantum number n and orbital angular momentum L. The lightfront AdS/QCD holographic approach thus gives a frameindependent representation of colorconfining dynamics and the excitation spectra of lightquark hadrons in terms of a single mass parameter. We also discuss the implications of the underlying conformal template of QCD for renormalization scalesetting and the implications of lightfront quantization for the value of the cosmological constant.  [Show abstract] [Hide abstract]
ABSTRACT: We review some outstanding puzzles and experimental anomalies in hadron physics that appear to challenge conventional wisdom and, in some cases, the foundations of QCD. We also discuss possible solutions and propose new tests and experiments that could illuminate the underlying physics and novel phenomenological features of QCD. In some cases, new perspectives for QCD physics have emerged.
Publication Stats
2k  Citations  
178.58  Total Impact Points  
Top Journals
Institutions

19772015

University of Costa Rica
 Escuela de Física
San José, San José, Costa Rica


19802014

Stanford University
 SLAC National Accelerator Laboratory
Stanford, California, United States


2008

École Polytechnique
 Centre de Physique Théorique
Paliseau, ÎledeFrance, France


1984

Harvard University
Cambridge, Massachusetts, United States
