117 research outputs found
Operators with Large Quantum Numbers, Spinning Strings, and Giant Gravitons
We study the behaviour of spinning strings in the background of various
distributions of smeared giant gravitons in supergravity. This gives insights
into the behaviour of operators of high dimension, spin and R-charge. Using a
new coordinate system recently presented in the literature, we find that it is
particularly natural to prepare backgrounds in which the probe operators
develop a variety of interesting new behaviours. Among these are the possession
of orbital angular momentum as well as spin, the breakdown of logarithmic
scaling of dimension with spin in the high spin regime, and novel
splitting/fractionation processes.Comment: 22 pages, 9 figures, LaTe
Universality in the Large N_c Dynamics of Flavour: Thermal Vs. Quantum Induced Phase Transitions
We show how two important types of phase transition in large N_c gauge theory
with fundamental flavours can be cast into the same classifying framework as
the meson-melting phase transition. These are quantum fluctuation induced
transitions in the presence of an external electric field, or a chemical
potential for R-charge. The classifying framework involves the study of the
local geometry of a special D-brane embedding, which seeds a self-similar
spiral structure in the space of embeddings. The properties of this spiral,
characterized by a pair of numbers, capture some key universal features of the
transition. Computing these numbers for these non-thermal cases, we find that
these transitions are in the same universality class as each other, but have
different universal features from the thermal case. We present a natural
generalization that yields new universality classes that may pertain to other
types of transition.Comment: 22 pages, 4 figures, pdfLaTe
Global Currents, Phase Transitions, and Chiral Symmetry Breaking in Large N_c Gauge Theory
We study, using a gravity dual, the finite temperature dynamics of
gauge theory for large , with fundamental quark flavours in a quenched
approximation, in the presence of a fixed R--charge under a global R--current.
We observe several notable phenomena. There is a first order phase transition
where the quark condensate jumps discontinuously at finite quark mass,
generalizing similar transitions seen at zero charge. Our tool in these studies
is holography, the string dual of the gauge theory being the geometry of
spinning D3--branes at finite temperature, probed by a D7--brane.Comment: (corrected version that appeared in JHEP
Quarks in an External Electric Field in Finite Temperature Large N Gauge Theory
We use a ten dimensional dual string background to aspects of the physics
large N four dimensional SU(N) gauge theory, where its fundamental quarks are
charged under a background electric field. The theory is N=2 supersymmetric for
vanishing temperature and electric field. At zero temperature, we observe that
the electric field induces a phase transition associated with the dissociation
of the mesons into their constituent quarks. This is an analogue of an
insulator-metal transition, since the system goes from being an insulator with
zero current (in the applied field) to a conductor with free charge carriers
(the quarks). At finite temperature this phenomenon persists, with the
dissociation transition become subsumed into the more familiar meson melting
transition. Here, the dissociation phenomenon reduces the critical melting
temperature.Comment: 20 pages, multiple figures. Corrected typo
Magnetic Catalysis in AdS4
We study the formation of fermion condensates in Anti de Sitter space. In
particular, we describe a novel version of magnetic catalysis that arises for
fermions in asymptotically AdS4 geometries which cap off in the infra-red with
a hard wall. We show that the presence of a magnetic field induces a fermion
condensate in the bulk that spontaneously breaks CP symmetry. From the
perspective of the dual boundary theory, this corresponds to a strongly coupled
version of magnetic catalysis in d=2+1.Comment: 22 pages, 4 figures. v2: References added, factors of 2 corrected,
extra comments added in appendix. v3: extra comments about fermion modes in a
hard wall background. v4: A final factor of
Dismantling monuments as the core of the post-2014 'decommunisation' in Ukraine and Poland
Drawing on a wide range of sources (Polish and Ukrainian legal acts, Russian and international media), this study looks at the 'monument fall' in Ukraine and Poland as part of the post-2014 memory wars. The purpose of this article is to identify the main patterns associated with the demolition of Soviet and Russian monuments in the two countries. The 'decommunisation' of public space is an element of Ukraine's and Poland's politics of memory, enshrined in legal acts. Its driving force is the Institutes of National Remembrance, whose priorities include dismantling Soviet and pre-revolutionary Russian monuments, which came into full swing after the beginning of Russia's special military operation to denazify and demilitarise Ukraine. The official narratives allot Poland and Ukraine the role of victims of 'two aggressors' in World War II, which found themselves under 'communist occupation'. Therefore, the politics of memory of the two countries seek to get rid of the 'Soviet legacy' as the legacy of the 'occupying country'. Whilst Poland pursues 'residual decommunisation' focused on dismantling the remaining memorials to Soviet soldiers-liberators, Ukraine is committed to transforming 'decommunisation' into full-scale 'derussification'. At the same time, the process of 're-Sovietisation/Sovietisation' has been launched in the liberated territories of Ukraine. It consists in restoring previously destroyed monuments or installing new ones
Universal Holographic Chiral Dynamics in an External Magnetic Field
In this work we further extend the investigation of holographic gauge
theories in external magnetic fields, continuing earlier work. We study the
phenomenon of magnetic catalysis of mass generation in 1+3 and 1+2 dimensions,
using D3/D7- and D3/D5-brane systems, respectively. We obtain the low energy
effective actions of the corresponding pseudo Goldstone bosons and study their
dispersion relations. The D3/D7 system exhibits the usual
Gell-Mann--Oakes--Renner (GMOR) relation and a relativistic dispersion
relation, while the D3/D5 system exhibits a quadratic non-relativistic
dispersion relation and a modified linear GMOR relation. The low energy
effective action of the D3/D5 system is related to that describing magnon
excitations in a ferromagnet. We also study properties of general Dp/Dq systems
in an external magnetic field and verify the universality of the magnetic
catalysis of dynamical symmetry breaking.Comment: 41 pages, 11 figures, references adde
D3/D7 Quark-Gluon Plasma with Magnetically Induced Anisotropy
We study the effects of the temperature and of a magnetic field in the setup
of an intersection of D3/D7 branes, where a large number of D7 branes is
smeared in the transverse directions to allow for a perturbative solution in a
backreaction parameter. The magnetic field sources an anisotropy in the plasma,
and we investigate its physical consequences for the thermodynamics and energy
loss of particles probing the system. In particular we comment on the
stress-energy tensor of the plasma, the propagation of sound in the directions
parallel and orthogonal to the magnetic field, the drag force of a quark moving
through the medium and jet quenching.Comment: 29 pages + appendices, 5 figures. v2 Version to appear in JHEP, with
minor revisions, references added and typos correcte
Dynamics of the chiral phase transition from AdS/CFT duality
We use Lorentzian signature AdS/CFT duality to study a first order phase
transition in strongly coupled gauge theories which is akin to the chiral phase
transition in QCD. We discuss the relation between the latent heat and the
energy (suitably defined) of the component of a D-brane which lies behind the
horizon at the critical temperature. A numerical simulation of a dynamical
phase transition in an expanding, cooling Quark-Gluon plasma produced in a
relativistic collision is carried out.Comment: 30 pages, 5 figure
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