766 research outputs found

### Fluid dynamics of R-charged black holes

We construct electrically charged AdS_5 black hole solutions whose charge,
mass and boost-parameters vary slowly with the space-time coordinates. From the
perspective of the dual theory, these are equivalent to hydrodynamic
configurations with varying chemical potential, temperature and velocity
fields. We compute the boundary theory transport coefficients associated with a
derivative expansion of the energy momentum tensor and R-charge current up to
second order. In particular, we find a first order transport coefficient
associated with the axial component of the current.Comment: 31 pages, v2: published version; added some references, discussion of
the charge-current changed, results unchanged, v3: typo in formula (15)
changed, v4: added footnote 3 in order to clarify the relation of our results
to those of arXiv:0809.259

### Chiral phase transitions and quantum critical points of the D3/D7(D5) system with mutually perpendicular E and B fields at finite temperature and density

We study chiral symmetry restoration with increasing temperature and density
in gauge theories subject to mutually perpendicular electric and magnetic
fields using holography. We determine the chiral symmetry breaking phase
structure of the D3/D7 and D3/D5 systems in the temperature-density-electric
field directions. A magnetic field may break the chiral symmetry and an
additional electric field induces Ohm and Hall currents as well as restoring
the chiral symmetry. At zero temperature the D3/D5 system displays a line of
holographic BKT phase transitions in the density-electric field plane, while
the D3/D7 system shows a mean-field phase transition. At intermediate
temperatures, the transitions in the density-electric field plane are of first
order at low density, transforming to second order at critical points as
density rises. At high temperature the transition is only ever first order.Comment: 15 pages, 7 figures, v2: Added a referenc

### Low-Energy Theorems from Holography

In the context of gauge/gravity duality, we verify two types of gauge theory
low-energy theorems, the dilation Ward identities and the decoupling of heavy
flavor. First, we provide an analytic proof of non-trivial dilation Ward
identities for a theory holographically dual to a background with gluon
condensate (the self-dual Liu--Tseytlin background). In this way an important
class of low-energy theorems for correlators of different operators with the
trace of the energy-momentum tensor is established, which so far has been
studied in field theory only. Another low-energy relationship, the so-called
decoupling theorem, is numerically shown to hold universally in three
holographic models involving both the quark and the gluon condensate. We show
this by comparing the ratio of the quark and gluon condensates in three
different examples of gravity backgrounds with non-trivial dilaton flow. As a
by-product of our study, we also obtain gauge field condensate contributions to
meson transport coefficients.Comment: 32 pages, 4 figures, two references added, typos remove

### Massive Quantum Liquids from Holographic Angel's Trumpets

We explore the small-temperature regime in the deconfined phase of massive
fundamental matter at finite baryon number density coupled to the 3+1
dimensional N=4 SYM theory. In this setting, we can demonstrate a new type of
non-trivial temperature-independent scaling solutions for the probe brane
embeddings. Focusing mostly on matter supported in 2+1 dimensions, the
thermodynamics indicate that there is a quantum liquid with interesting
density-dependent low-temperature physics. We also comment about 3+1 and 1+1
dimensional systems, where we further find for example a new thermodynamic
instability.Comment: 18+1 pages, 6 figures; replaced fig. 6 and comments in sec. 5.2;
minor explanations added and typos fixed, final version published in JHEP
(modulo fig. 3); factor of \sqrt{\lambda} and corresponding comments fixe

### Towards quantifying information flows: Relative entropy in deep neural networks and the renormalization group

We investigate the analogy between the renormalization group (RG) and deep neural networks, wherein subsequent layers of neurons are analogous to successive steps along the RG. In particular, we quantify the flow of information by explicitly computing the relative entropy or Kullback-Leibler divergence in both the one- and two-dimensional Ising models under decimation RG, as well as in a feedforward neural network as a function of depth. We observe qualitatively identical behavior characterized by the monotonic increase to a parameter-dependent asymptotic value. On the quantum field theory side, the monotonic increase confirms the connection between the relative entropy and the c-theorem. For the neural networks, the asymptotic behavior may have implications for various information maximization methods in machine learning, as well as for disentangling compactness and generalizability. Furthermore, while both the two-dimensional Ising model and the random neural networks we consider exhibit non-trivial critical points, the relative entropy appears insensitive to the phase structure of either system. In this sense, more refined probes are required in order to fully elucidate the flow of information in these models. (C) Copyright J. Erdmenger et al. This work is licensed under the Creative Commons Attribution 4.0 International License. Published by the SciPost Foundation

### Strongly bound mesons at finite temperature and in magnetic fields from AdS/CFT

We study mesons in N=4 super Yang-Mills theory with fundamental flavors added
at large 't Hooft coupling using the gauge/gravity correspondence. High-spin
mesons are well described by using semiclassical string configurations. We
determine the meson spectrum at finite temperature and in a background magnetic
field.Comment: 15 pages, 11 figures; v2: references adde

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