6 research outputs found
Holographic Wilsonian Renormalization and Chiral Phase Transitions
We explore the role of a holographic Wilsonian cut-off in simple probe brane
models with chiral symmetry breaking/restoration phase transitions. The
Wilsonian cut-off allows us to define supergravity solutions for off-shell
configurations and hence to define a potential for the chiral condensate. We
pay particular attention to the need for configurations whose action we are
comparing to have the same IR and UV boundary conditions. We exhibit new first
and second order phase transitions with changing cut-off. We derive the
effective potential for the condensate including mean field and BKT type
continuous transitions.Comment: 14 pages, 16 figures, v2: Added references, corrected typos, v3:
minor corrections, the version to appear in PR
Phase diagram of the D3/D5 system in a magnetic field and a BKT transition
We study the full temperature and chemical potential dependence of the D3/D5
2+1 dimensional theory in the presence of a magnetic field. The theory displays
separate transitions associated with chiral symmetry breaking and melting of
the bound states. We display the phase diagram which has areas with first and
second order transitions meeting at two critical points similar to that of the
D3/D7 system. In addition there is the recently reported BKT transition at zero
temperature leading to distinct structure at low temperatures.Comment: 5 pages, 3 figures, V2: references adde
The Baryonic Phase in Holographic Descriptions of the QCD Phase Diagram
We study holographic models of the QCD temperature-chemical potential phase
diagram based on the D3/D7 system with chiral symmetry breaking. The baryonic
phase may be included through linked D5-D7 systems. In a previous analysis of a
model with a running gauge coupling a baryonic phase was shown to exist to
arbitrarily large chemical potential. Here we explore this phase in a more
generic phenomenological setting with a step function dilaton profile. The
change in dilaton generates a linear confining potential and opposes
the screening effect of temperature. We show that the persistence of the
baryonic phase depends on the step size and that QCD-like phase diagrams can be
described. The baryonic phase's existence is qualitatively linked to the
existence of confinement in Wilson loop computations in the background.Comment: 21 pages, 7 figure
Towards a Holographic Model of the QCD Phase Diagram
We describe the temperature-chemical potential phase diagrams of holographic
models of a range of strongly coupled gauge theories that display chiral
symmetry breaking/restoration transitions. The models are based on the
D3/probe-D7 system but with a phenomenologically chosen running
coupling/dilaton profile. We realize chiral phase transitions with either
temperature or density that are first or second order by changing the dilaton
profile. Although the models are only caricatures of QCD they show that
holographic models can capture many aspects of the QCD phase diagram and hint
at the dependence on the running coupling.Comment: 11 pages, 9 figures, v2: minor corrections, Invited contribution to
an AdS/CFT edition of Journal of Physics
Holographic descriptions of chiral phase transitions
Quantum Chromodynamics (QCD) poses a challenge in calculating physical phenomena in low energy scales due to its strongly coupled character. The tools available for understanding this region of QCD are limited. One such tool is gauge/gravity duality which promises to attack strongly coupled related phenomena, at least in a qualitative level, by using the conjectured equivalence between string theory and some classes of quantum field theories (gauge/gravity duality). In this thesis strongly coupled 3+1d and 2+1d field theories are explored by using D3/D7 and D3/D5 brane systems respectively. These theories exhibit some QCD-like characteristics like chiral symmetry breaking and confinement. The main focus of the following chapters is understanding chiral phase transitions in those theories and constructing their phase diagrams in finite temperature and chemical potential. Chiral symmetry breaking is induced in these holographic brane setups by turning on a background magnetic field or by choosing an appropriate running dilaton profile. The phase diagrams for each field theory considered are mapped, giving a rich structure of first, second and BKT holographic transitions. Some successful attempts where made to reproduce the standard QCD phase diagram, in the running dilaton scenario. Also, in the running dilaton case wrapped D5 branes where used to introduce holographic baryons. The baryonic phase, for some range of the parameter space, participates in the phase diagram and it is found in the regime expected from QCD. Finally, chiral phase transitions with energy scale where explored as well as their holographic effective potentials for various D3/D7 and D3/D5 systems
Holographic description of the phase diagram of a chiral symmetry breaking gauge theory
The large N_c N=4 gauge theory with quenched N=2 quark matter in the presence of a magnetic field displays chiral symmetry breaking. We study the temperature and chemical potential dependence of this theory using its gravity dual (based on the D3/D7 brane system). With massless quarks, at zero chemical potential, the theory displays a first order thermal transition where chiral symmetry is restored and simultaneously the mesons of the theory melt. At zero temperature, these transitions with chemical potential are second order and occur at different chemical potential values. Between the three there are two tri-critical points, the positions of which we identify. At finite quark mass the second order transition for chiral symmetry becomes a cross over and there is a critical point at the end of the first order transition, while the meson melting transition remains similar to the massless quark case. We track the movement of the critical points as the mass is raised relative to the magnetic field. <br/