arXiv subjects

Chung-I Tan

Publications and source records attributed to Chung-I Tan.

At least 55 records · Page 3Linked to original sources

arXiv2007

Glueball Decay in Holographic QCD

Using holographic QCD based on D4-branes and D8-anti-D8-branes, we have computed couplings of glueballs to light mesons. We describe glueball decay by explicitly calculating its decay widths and branching ratios. Interestingly, while glueballs remain less well understood both theoretically and experimentally, our results are found to be consistent with the experimental data for the scalar glueball candidate f_0(1500). More generally, holographic QCD predicts that decay of any glueball to 4 $π_0$ is surpressed, and that mixing of the lightest glueball with $q\bar{q}$ mesons is small.

hep-th↗

arXiv2007

Analytic Expression for the Joint x and Q^2 Dependences of the Structure Functions of Deep Inelastic Scattering

We obtain a good analytic fit to the joint Bjorken-x and Q^2 dependences of ZEUS data on the deep inelastic structure function F_2(x, Q^2). At fixed virtuality Q^2, as we showed previously, our expression is an expansion in powers of log (1/x) that satisfies the Froissart bound. Here we show that for each x, the Q^2 dependence of the data is well described by an expansion in powers of log Q^2. The resulting analytic expression allows us to predict the logarithmic derivatives {({\partial}^n F_2^p/{(\partial\ln Q^2})^n)}_x for n = 1,2 and to compare the results successfully with other data. We extrapolate the proton structure function F_2^p(x,Q^2) to the very large Q^2 and the very small x regions that are inaccessible to present day experiments and contrast our expectations with those of conventional global fits of parton distribution functions.

hep-ph↗

arXiv2006

String/Flux Tube Duality on the Lightcone

The equivalence of quantum field theory and string theory as exemplified by the AdS/CFT correspondence is explored from the point of view of lightcone quantization. On the string side we discuss the lightcone version of the static string connecting a heavy external quark source to a heavy external antiquark source, together with small oscillations about the static string configuration. On the field theory side we analyze the weak/strong coupling transition in a ladder diagram model of the quark antiquark system, also from the point of view of the lightcone. Our results are completely consistent with those obtained by more standard covariant methods in the limit of infinitely massive quarks.

hep-th↗

arXiv2005

Probing the 5th Dimension with the QCD String

A salient feature of String/Gauge duality is an extra 5th dimension. Here we study the effect of confining deformations of AdS5 and compute the spectrum of a string stretched between infinitely massive quarks and compare it with the quantum states of the QCD flux as determined by Kuti, Juge and Morningstar in lattice simulations. In the long flux tube limit the AdS string probes the metric near the IR cutoff of the 5th dimension with a spectrum approximated by a Nambu-Goto string in 4-d flat space, whereas at short distance the string moves to the UV region with a discrete spectrum for pure AdS5. We also review earlier results on glueballs states and the cross-over between hard and soft diffractive scattering that support this picture.

hep-th↗

arXiv2002

Hagedorn transition for strings on pp-waves and tori with chemical potentials

It has been conjectured that string theory in a pp-wave background is dual to a sector of N=4 supersymmetric Yang-Mills theory. We study the Hagedorn transition for free strings in this background. We find that the free energy at the transition point is finite suggesting a confinement/deconfinement transition in the gauge theory. In the limit of vanishing mass parameter the free energy matches that of free strings on an 8-torus with momentum/winding chemical potential. The entropy in the microcanonical ensemble with fixed energy and fixed momentum/winding is computed in each case.

hep-th↗

arXiv2002

Brane World Gravity in an AdS Black Hole

We consider a model of brane world gravity in the context of non-conformal non-SUSY matter. In particular we modify the earlier strong coupling solution to the glueball spectrum in an $AdS^7$ Black Hole by introducing a Randall-Sundrum Planck brane as a UV cut-off. The consequence is a new normalizable zero mass tensor state, which gives rise to an effective Einstein-Hilbert theory of gravity, with exponentially small corrections set by the mass gap to the discrete glueball spectrum. However the simplest microscopic theory for the Planck brane is found to have a tachyonic instability in the radion mode.

hep-th↗

arXiv2001

Pomeron and AdS/CFT Correspondence for QCD

The Maldacena conjecture that QCD is holographically dual to gravity in extra dimensions is briefly reviewed. On the basis of this duality conjecture, the complete glueball spectrum is computed which bares a striking resemblance to the known $QCD_4$ spectrum as determined by lattice simulations. In particular, a strong coupling expansion for the Pomeron intercept is obtained.

hep-ph↗

arXiv2000

From Black Holes to Pomeron: Tensor Glueball and Pomeron Intercept at Strong Coupling

We briefly review the approach for strong coupling calculation of glueball masses based on the duality between supergravity and Yang-Mills theory. Earlier work is extended to non-zero spin. Fluctuations in the gravitational metric lead to the $2^{++}$ tensor glueball state on the leading Pomeron trajectory with a mass relation: $m(0^{++}) < m(2^{++}) $. In particular, for $QCD_4$, a strong coupling expansion for the Pomeron intercept is obtained.

hep-ph↗

arXiv2000

Glueball Spectrum for QCD from AdS Supergravity Duality

We present the analysis of the complete glueball spectrum for the $AdS^7$ black hole supergravity dual of $QCD_4$ in strong coupling limit: $g^2 N \to \infty$. The bosonic fields in the supergravity multiplet lead to 6 independent wave equations contributing to glueball states with $J^{PC} = 2^{++},1^{+-}, 1^{--}$, $0^{++}$ and $0^{-+}$. We study the spectral splitting and degeneracy patterns for both $QCD_4$ and $QCD_3$. Despite the expected limitations of a leading order strong coupling approximation, the pattern of spins, parities and mass inequalities bear a striking resemblance to the known $QCD_4$ glueball spectrum as determined by lattice simulations at weak coupling.

hep-th↗

arXiv1999

From Black Holes to Glueballs: The QCD_3 Tensor Glueball at Strong Coupling

A strong coupling calculation of glueball masses based on the duality between supergravity and Yang-Mills theory is presented. Earlier work is extended to non-zero spin. Fluctuations in the gravitational metric lead to the 2^{++} state on the leading Pomeron trajectory with a mass relation: m(0^{++}) < m(2^{++}) < m(1^{-+}). Contrary to expectation, the mass of our new 0^{++} state (m^2=5.4573) associated with the graviton is smaller than the mass of the ${\tilde 0}^{++}$ state (m^2=11.588) from the dilaton, which in fact is exactly degenerate with the tensor 2^{++}.

hep-lat↗

arXiv1999

Discrete Spectrum of the Graviton in the $AdS^5$ Black Hole Background

The discrete spectrum of fluctuations of the metric about an $AdS^5$ black hole background are found. These modes are the strong coupling limit of so called glueball states in a dual 3-d Yang-Mills theory with quantum numbers $J^{PC} = 2^{++}, 1^{-+}, 0^{++}$. For the ground state modes, we find the mass relation: $m(0^{++}) < m(2^{++}) < m(1^{-+})$. Contrary to expectation, the mass of our new $0^{++}$ state ($m^2=5.4573$) associated with the graviton is smaller than the mass of the $0^{++}$ state ($m^2=11.588$) from the dilaton. In fact the dilatonic excitations are exactly degenerate with our tensor $2^{++}$ states. We find that variational methods gives remarkably accurate mass estimates for all three low-lying levels while a WKB treatment describes the higher modes well.

hep-th↗

arXiv1998

Diffractive Production at Collider Energies and Factorization

The most important consequence of Pomeron being a pole is the factorization property. However, due to Pomeron intercept being greater than 1, the extrapolated single diffraction dissociation cross section based on a classical triple-Pomeron formula is too large leading to a potential unitarity violation at Tevatron energies, which has been referred to as "Dino's paradox". We review our resolution which involves a proper implementation of final-state screening correction, with "flavoring" for Pomeron as the primary dynamical mechanism for setting the relevant energy scale. In this approach, factorization remains intact, and unambiguous predictions for double Pomeron exchange, doubly diffraction dissociation, etc., both at Tevatron and at LHC energies, can be made.

hep-ph↗

arXiv1998

Diffraction Association and Flavoring of Pomeron

hep-ph↗

arXiv1997

Flavoring of Pomeron and Diffractive Production at Tevatron Energies

hep-ph↗

arXiv1997

Diffractive Production at Collider - I: Soft Diffraction and Dino's Paradox

One of the more interesting developments from recent collider experiments is the finding that hadronic total cross sections as well as elastic cross s ections can be described by the exchange of a "soft Pomeron" pole in the near-forward limit. The most impor tant consequence of Pomeron being a pole is the factorization property. However, due to Pomeron intercept being greater than 1, the extrapolated single diffraction dissociation cross section based on a classical triple-Pomeron formula is too large leading to a potential unitarity violation at Tevatron energies. It is our desire here to examine carefully the notion of Pomeron flux renormalization, proposed by Goulianos, and to suggest an alternative resol ution. Our treatment lies in a proper implementation of final-state screening correction, with "flavoring" for Pomeron as the primary dynamical mechanism for setting the relevant energy s cale. In our scheme, which we shall occasionally refer to as ``unitarization of Pomeron flux", initia l-state screening remains unimportant, consistent with the pole dominance picture for elastic and total cross section hypothesis at Tevatron energies. Since factorization remains intact, umambiguo us predictions for double Pomeron exchange, doubly diffraction dissociation, etc., both at Tevatron and at LHC energies, can be made.

hep-ph↗

arXiv1996

Magnetic monopole loop for the Yang-Mills instanton

We investigate 't Hooft-Mandelstam monopoles in QCD in the presence of a single classical instanton configuration. The solution to the Maximal Abelian projection is found to be a circular monopole trajectory with radius $R$ centered on the instanton. At zero loop radius, there is a marginally stable (or flat) direction for loop formation to $O(R^4 logR)$. We argue that loops will form, in the semi-classical limit, due to small perturbations such as the dipole interaction between instanton anti-instanton pairs. As the instanton gas becomes a liquid, the percolation of the monopole loops may therefore provide a semi-classical precursor to the confinement mechanism.

hep-th↗

arXiv1994

Simplicial Chiral Models

Principal chiral models on a d-1 dimensional simplex are introduced and studied analytically in the large $N$ limit. The $d = 0, 2, 4$ and $\infty$ models are explicitly solved. Relationship with standard lattice models and with few-matrix systems in the double scaling limit are discussed.

hep-th↗

arXiv1994

High energy Scattering in 2+1 QCD: A Dipole Picture

A dipole picture of high energy scattering is developed in the 2+1 dimensional QCD, following Mueller. A generalized integral equation for the dipole density with a given separation and center of mass position is derived, and meson-meson non-forward scattering amplitude is therefore calculated. We also calculate the amplitude due to two pomeron exchange, and the triple pomeron coupling. We compare the result obtained by this method to our previous result based on an effective action approach, and find the two results agree at the one pomeron exchange level.

hep-ph↗