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Digital archive of theses discussed at the University of Pisa

 

Thesis etd-05252016-020254


Thesis type
Tesi di laurea magistrale
Author
MANENTI, ANDREA
URN
etd-05252016-020254
Thesis title
Holographic computation of the Neutron Electric Dipole Moment
Department
FISICA
Course of study
FISICA
Supervisors
relatore Dott. Bigazzi, Francesco
Keywords
  • AdS/CFT correspondence
  • Chromodynamics
  • dipole moment
  • gauge gravity duality
  • holography
  • instantons
  • QCD
  • string theory
  • topological term
Graduation session start date
21/07/2016
Availability
Full
Summary
The final aim of the thesis is the computation of the Neutron electric dipole moment in the theory of
Quantum Chromodynamics. This quantity is easily accessible experimentally and it is P and T violating,
so the physical interest consists in the possibility of investigating an eventual P, T violation in QCD.
The computation will be performed in the framework of AdS/CFT correspondence, in particular we
use the Sakai–Sugimoto model, in which some deformation are added in order to include masses to
quarks and a non zero theta parameter. The baryons in this model correspond to instantons in a Yang-Mills - Chern-Simons theory, in analogy with the Skyrme model where they correspond to Skyrmions.
Standard quantum mechanic techniques allow us to quantize these solution and to study their properties,
such as the electric dipole moment.
The work will be organized as follows: first of all we make an introduction to the AdS/CFT cor-
respondence, the basic tools of String theory, AdS geometry and D-branes are briefly summarized and
then combined to formulate the correspondence, along with a simple example. After this we discuss some
important non perturbative aspects of QCD, among them the topological properties,
instantons and large N expansion. Then we focus on the Witten's background for QCD, obtained
from a supersymmetry breaking compactification in Type II A Supergravity, this is interpreted as a dual
of Yang-Mills at low energies. Then the Sakai-Sugimoto model is introduced, which is a setting of
D8 branes in the Witten's background, this allows us to describe massless quarks. We then move to
the necessary deformations needed to pursue our final computation. Masses to quarks are introduced via
a non local term, they are necessary to have a non trivial theta dependence because the U(1)A anomaly
has naturally an holographic counterpart. The theta parameter is simply related to a background value of
the RR 1 form, which, when the masses are present, can be absorbed in the abelian gauge field. Then
follows a review of the instantonic solution of this model, its moduli space and the quantization. This
solution is the holographic dual of a baryon, we compute in addition the correction to the baryon mass
in presence of a theta parameter. The last part is the actual computation of the electric dipole moment of
the neutron, some previous results obtained with different methods are shown. First of all we solve the
Yang-Mills - Chern-Simons equations of motion on the D8 branes in presence of the mass perturbation,
then we quantize the solution via standard methods and extract the Neutron Electric Dipole moment, to
first order in the quark masses and in the theta parameter, in the case of two degenerate flavours. The idea
of the computation is inspired to the Skyrme model's counterpart.
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