Physics Letters B 746 (2015) 285–292
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Improvements to the Froissart bound from AdS/CFT
Verónica Errasti Díez
a,b,∗
, Rohini M. Godbole
a
, Aninda Sinha
a
a
Centre for High Energy Physics, Indian Institute of Science, Bangalore 560012, India
b
Physics Department, McGill University, 3600 University St, Montréal, QC H3A 2T8, Canada
a r t i c l e i n f o a b s t r a c t
Article history:
Received
5 May 2015
Accepted
7 May 2015
Available
online 13 May 2015
Editor: L.
Alvarez-Gaumé
In this paper we consider the issue of the Froissart bound on the high energy behaviour of total cross
sections. This bound, originally derived using principles of analyticity of scattering amplitudes, is seen
to be satisfied by all the available experimental data on total hadronic cross sections. At strong cou-
pling,
gauge/gravity duality has been used to provide some insights into this behaviour. In this work,
we find the subleading terms to the so-derived Froissart bound from AdS/CFT. We find that a (ln
s
s
0
)
term is obtained, with a negative coefficient. We see that the fits to the currently available data confirm
improvement in the fits due to the inclusion of such a term, with the appropriate sign.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The high energy behaviour of the total cross sections for the
scattering of any two high energy particles has been a subject
of great theoretical interest over many decades, beginning from
Heisenberg [1]. The various bounds one obtains on the rate of
the rise of these cross sections are based just on the analyticity
properties of scattering amplitudes and do not use any knowledge
of the underlying dynamics of the interaction responsible for the
scattering. The most important of all these has been the Froissart
bound [2,3], which states that at high energies, the total cross sec-
tion
for a scattering process 1 +2 → f ( f =any final state) has an
upper bound ∼ (ln
2
s
s
0
). Here
√
s is the centre of mass energy and
√
s
0
is an energy scale. Since the bound can be derived from very
general physical arguments, such as the unitarity of the S matrix
and certain analytical properties of the scattering amplitude, it has
to be true in any quantum field theory. However, to derive this
in the context of theories of strong interactions, like QCD, one re-
quires
to handle the theory in the non-perturbative regime. As a
result, there exist only models and these usually try to incorporate
known properties of QCD, the modelling aspect involving assump-
tions
and ansaetze about the non-perturbative regime [4–11]. In
fact, analyses of [9,12] in the framework of the Bloch–Nordsiek
improved eikonalised mini jet model [13] indicate a direct relation-
ship
between the Froissart bound at high energy and the dynamics
*
Corresponding author at: Physics Department, McGill University, 3600 Univer-
sity St,
Montréal, QC H3A 2T8, Canada.
E-mail
addresses: vediez@physics.mcgill.ca (V. Errasti Díez),
rohini@cts.iisc.ernet.in (R.M. Godbole), asinha@cts.iisc.ernet.in (A. Sinha).
of ultra soft gluons, i.e., the behaviour of QCD in the far infrared.
An analysis of the high energy behaviour of the available data on
total hadronic cross sections, while being completely consistent
with the bound, seems to need in the fits the presence of a sub-
leading
(ln
s
s
0
) term to the Froissart bound. Various QCD (inspired)
models use such a subleading term, though there is no theory with
a proper explanation of this subleading behaviour [8,14–16].
In this article, we attempt to seek a theoretical understanding
of this subleading behaviour shown by the data on total cross sec-
tions
at high energies, using the AdS/CFT correspondence [17]. It
is known that the leading term (Froissart bound) can be derived
using AdS/CFT [18–20]. The model based on [21] describes high
energy scattering in a large-N, large-λ gauge theory with broken
conformal symmetry which is achieved by putting a cut-off in the
infra-red (IR). Here N is the number of colours and λ is the ’t Hooft
coupling. When a point mass m is placed on the IR boundary,
the perturbations in the AdS space can be big enough to create
a black hole. The geometrical cross section of such a black hole,
whose radius is equal to the AdS radius, is the gravity dual of the
maximum possible scattering cross section in the field theory. In
order to have a more realistic model, which takes into account
finite coupling corrections (in 1/N and 1/λ), we can incorporate
higher curvature corrections in the dual gravity description. If we
are working perturbatively in the couplings, then the leading cor-
rection
of this type will be at four-derivative order [22]. Such terms
can be redefined into a single Gauss–Bonnet term whose coeffi-
cient
describes a 1/N correction – see e.g. [23] for the dictionary
relating the field theory to gravity in such a theory. As we will ar-
gue
below, this result will in fact hold for any higher curvature
gravity dual based on the results in [24]. In [19,20] it is argued
http://dx.doi.org/10.1016/j.physletb.2015.05.016
0370-2693/
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.