1,244 research outputs found
High--Energy Photon--Hadron Scattering in Holographic QCD
This article provides an in-depth look at hadron high energy scattering by
using gravity dual descriptions of strongly coupled gauge theories. Just like
deeply inelastic scattering (DIS) and deeply virtual Compton scattering (DVCS)
serve as clean experimental probes into non-perturbative internal structure of
hadrons, elastic scattering amplitude of a hadron and a (virtual) "photon" in
gravity dual can be exploited as a theoretical probe. Since the scattering
amplitude at sufficiently high energy (small Bjorken x) is dominated by parton
contributions (= Pomeron contributions) even in strong coupling regime, there
is a chance to learn a lesson for generalized parton distribution (GPD) by
using gravity dual models. We begin with refining derivation of
Brower-Polchinski-Strassler-Tan (BPST) Pomeron kernel in gravity dual, paying
particular attention to the role played by complex spin variable j. The BPST
Pomeron on warped spacetime consists of a Kaluza-Klein tower of 4D Pomerons
with non-linear trajectories, and we clarify the relation between Pomeron
couplings and Pomeron form factor. We emphasize that the saddle point value j^*
of the scattering amplitude in the complex j-plane representation is a very
important concept in understanding qualitative behavior of the scattering
amplitude. The total Pomeron contribution to the scattering is decomposed into
the saddle point contribution and at most a finite number of pole
contributions, and when the pole contributions are absent (which we call saddle
point phase), kinematical variable (q,x,t) dependence of ln (1/q) evolution and
ln(1/x) evolution parameters gamma_eff. and lambda_eff. in DIS and t-slope
parameter B of DVCS in HERA experiment are all reproduced qualitatively in
gravity dual
The Pomeron and Gauge/String Duality
The traditional description of high-energy small-angle scattering in QCD has
two components -- a soft Pomeron Regge pole for the tensor glueball, and a hard
BFKL Pomeron in leading order at weak coupling. On the basis of gauge/string
duality, we present a coherent treatment of the Pomeron. In large-N QCD-like
theories, we use curved-space string-theory to describe simultaneously both the
BFKL regime and the classic Regge regime. The problem reduces to finding the
spectrum of a single j-plane Schrodinger operator. For ultraviolet-conformal
theories, the spectrum exhibits a set of Regge trajectories at positive t, and
a leading j-plane cut for negative t, the cross-over point being
model-dependent. For theories with logarithmically-running couplings, one
instead finds a discrete spectrum of poles at all t, where the Regge
trajectories at positive t continuously become a set of slowly-varying and
closely-spaced poles at negative t. Our results agree with expectations for the
BFKL Pomeron at negative t, and with the expected glueball spectrum at positive
t, but provide a framework in which they are unified. Effects beyond the single
Pomeron exchange are briefly discussed.Comment: 68 pages, uses JHEP3.cls, utphys.bst; references added, typos
corrected, and clarifying remarks adde
A Mutually-Dependent Hadamard Kernel for Modelling Latent Variable Couplings
We introduce a novel kernel that models input-dependent couplings across
multiple latent processes. The pairwise joint kernel measures covariance along
inputs and across different latent signals in a mutually-dependent fashion. A
latent correlation Gaussian process (LCGP) model combines these non-stationary
latent components into multiple outputs by an input-dependent mixing matrix.
Probit classification and support for multiple observation sets are derived by
Variational Bayesian inference. Results on several datasets indicate that the
LCGP model can recover the correlations between latent signals while
simultaneously achieving state-of-the-art performance. We highlight the latent
covariances with an EEG classification dataset where latent brain processes and
their couplings simultaneously emerge from the model.Comment: 17 pages, 6 figures; accepted to ACML 201
Probing the light radion through diphotons at the Large Hadron Collider
A radion in a scenario with a warped extra dimension can be lighter than the
Higgs boson, even if the Kaluza-Klein excitation modes of the graviton turn out
to be in the multi-TeV region. The discovery of such a light radion would be
gateway to new physics. We show how the two-photon mode of decay can enable us
to probe a radion in the mass range 60 - 110 GeV. We take into account the
diphoton background, including fragmentation effects, and include cuts designed
to suppress the background to the maximum possible extent. Our conclusion is
that, with an integrated luminosity of 3000 or less, the next run
of the Large Hadron Collider should be able to detect a radion in this mass
range, with a significance of 5 standard deviations or more.Comment: 24 pages, 4 figures, Version published in Phys. Rev.
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