1,927 research outputs found
Charged Magnetic Brane Solutions in AdS_5 and the fate of the third law of thermodynamics
We construct asymptotically AdS_5 solutions to 5-dimensional Einstein-Maxwell
theory with Chern-Simons term which are dual to 4-dimensional gauge theories,
including N=4 SYM theory, in the presence of a constant background magnetic
field B and a uniform electric charge density \rho. For the solutions
corresponding to supersymmetric gauge theories, we find numerically that a
small magnetic field causes a drastic decrease in the entropy at low
temperatures. The near-horizon AdS_2 \times R^3 geometry of the purely
electrically charged brane thus appears to be unstable under the addition of a
small magnetic field. Based on this observation, we propose a formulation of
the third law of thermodynamics (or Nernst theorem) that can be applied to
black holes in the AdS/CFT context.
We also find interesting behavior for smaller, non-supersymmetric, values of
the Chern-Simons coupling k. For k=1 we exhibit exact solutions corresponding
to warped AdS_3 black holes, and show that these can be connected to
asymptotically AdS_5 spacetime. For k\leq 1 the entropy appears to go to a
finite value at extremality, but the solutions still exhibit a mild singularity
at strictly zero temperature. In addition to our numerics, we carry out a
complete perturbative analysis valid to order B^2, and find that this
corroborates our numerical results insofar as they overlap.Comment: 45 pages v2: added note about subsequent results found in
arXiv:1003.130
Evaluating noninvasive markers of nonhuman primate immune activation and inflammation.
OBJECTIVES: Health, disease, and immune function are key areas of research in studies of ecology and evolution, but work on free-ranging primates has been inhibited by a lack of direct noninvasive measures of condition. Here, we evaluate the potential usefulness of noninvasive measurement of three biomarkers, the acute-phase proteins C-reactive protein (CRP) and haptoglobin, and neopterin, a by-product of macrophage activity. MATERIALS AND METHODS: We took advantage of veterinary checks on captive rhesus (24) and long-tailed (3) macaques at the German Primate Center (DPZ) to analyze serum marker measures, before measuring concentrations in feces and urine, and evaluating relationships between matched serum, urine, and fecal concentrations. In a second study, we monitored excretion of these markers in response to simian immunodeficiency virus (SIV) infection and surgical tissue trauma, undertaken for a separate study. RESULTS: We found that each biomarker could be measured in each matrix. Serum and urinary concentrations of neopterin were strongly and significantly correlated, but neither haptoglobin nor CRP concentrations in excreta proxied circulating serum concentrations. Our infection study confirmed that urinary neopterin, in particular, is a reliable marker of viral infection in macaques, but also indicated the potential of urinary and fecal CRP and haptoglobin as indicators of inflammation. DISCUSSION: We highlight the potential of noninvasive markers of immune function, especially of urinary neopterin, which correlates strongly with serum neopterin, and is highly responsive to infection. Am J Phys Anthropol 158:673-684, 2015. © 2015 Wiley Periodicals, Inc
Holographic Metamagnetism, Quantum Criticality, and Crossover Behavior
Using high-precision numerical analysis, we show that 3+1 dimensional gauge
theories holographically dual to 4+1 dimensional Einstein-Maxwell-Chern-Simons
theory undergo a quantum phase transition in the presence of a finite charge
density and magnetic field. The quantum critical theory has dynamical scaling
exponent z=3, and is reached by tuning a relevant operator of scaling dimension
2. For magnetic field B above the critical value B_c, the system behaves as a
Fermi liquid. As the magnetic field approaches B_c from the high field side,
the specific heat coefficient diverges as 1/(B-B_c), and non-Fermi liquid
behavior sets in. For B<B_c the entropy density s becomes non-vanishing at zero
temperature, and scales according to s \sim \sqrt{B_c - B}. At B=B_c, and for
small non-zero temperature T, a new scaling law sets in for which s\sim
T^{1/3}. Throughout a small region surrounding the quantum critical point, the
ratio s/T^{1/3} is given by a universal scaling function which depends only on
the ratio (B-B_c)/T^{2/3}.
The quantum phase transition involves non-analytic behavior of the specific
heat and magnetization but no change of symmetry. Above the critical field, our
numerical results are consistent with those predicted by the Hertz/Millis
theory applied to metamagnetic quantum phase transitions, which also describe
non-analytic changes in magnetization without change of symmetry. Such
transitions have been the subject of much experimental investigation recently,
especially in the compound Sr_3 Ru_2 O_7, and we comment on the connections.Comment: 23 pages, 8 figures v2: added ref
Nummular keratopathy in a patient with Hyper-IgD Syndrome
<p>Abstract</p> <p>Purpose</p> <p>To report a case of recurrent nummular keratitis in a pediatric patient with Hyperimmunoglobulinemia D syndrome.</p> <p>Methods</p> <p>A retrospective chart review.</p> <p>Results</p> <p>A 14-year-old boy with Hyperimmunoglobulinemia D syndrome (HIDS) presented with photophobia and ocular irritation concomitant with disease exacerbation. He was found on exam to have significant nummular keratitis, which responded to a short course of topical steroids. Despite acute response to local immunosuppression, the patient had several recurrent attacks and eventually developed a large corneal scar and decreased vision. After initiation of infliximab therapy his ocular sequelae improved dramatically and his vision returned to 20/20.</p> <p>Conclusion</p> <p>One possible form of end-organ damage associated with HIDS is vision threatening nummular keratopathy.</p
Universality and exactness of Schrodinger geometries in string and M-theory
We propose an organizing principle for classifying and constructing
Schrodinger-invariant solutions within string theory and M-theory, based on the
idea that such solutions represent nonlinear completions of linearized vector
and graviton Kaluza-Klein excitations of AdS compactifications. A crucial
simplification, derived from the symmetry of AdS, is that the nonlinearities
appear only quadratically. Accordingly, every AdS vacuum admits infinite
families of Schrodinger deformations parameterized by the dynamical exponent z.
We exhibit the ease of finding these solutions by presenting three new
constructions: two from M5 branes, both wrapped and extended, and one from the
D1-D5 (and S-dual F1-NS5) system. From the boundary perspective, perturbing a
CFT by a null vector operator can lead to nonzero beta-functions for spin-2
operators; however, symmetry restricts them to be at most quadratic in
couplings. This point of view also allows us to easily prove nonrenormalization
theorems: for any Sch(z) solution of two-derivative supergravity constructed in
the above manner, z is uncorrected to all orders in higher derivative
corrections if the deforming KK mode lies in a short multiplet of an AdS
supergroup. Furthermore, we find infinite classes of 1/4 BPS solutions with
4-,5- and 7-dimensional Schrodinger symmetry that are exact.Comment: 31 pages, plus appendices; v2, minor corrections, added refs, slight
change in interpretation in section 2.3, new Schrodinger and Lifshitz
solutions included; v3, clarifications in sections 2 and 3 regarding
existence of solutions and multi-trace operator
Schr\"odinger Deformations of AdS_3 x S^3
We study Schr\"odinger invariant deformations of the AdS_3 x S^3 x T^4 (or
K3) solution of IIB supergravity and find a large class of solutions with
integer and half-integer dynamical exponents. We analyze the supersymmetries
preserved by our solutions and find an infinite number of solutions with four
supersymmetries. We study the solutions holographically and find that the dual
D1-D5 (or F1-NS5) CFT is deformed by irrelevant operators of spin one and two.Comment: 23 page
Realisation of a programmable two-qubit quantum processor
The universal quantum computer is a device capable of simulating any physical
system and represents a major goal for the field of quantum information
science. Algorithms performed on such a device are predicted to offer
significant gains for some important computational tasks. In the context of
quantum information, "universal" refers to the ability to perform arbitrary
unitary transformations in the system's computational space. The combination of
arbitrary single-quantum-bit (qubit) gates with an entangling two-qubit gate is
a gate set capable of achieving universal control of any number of qubits,
provided that these gates can be performed repeatedly and between arbitrary
pairs of qubits. Although gate sets have been demonstrated in several
technologies, they have as yet been tailored toward specific tasks, forming a
small subset of all unitary operators. Here we demonstrate a programmable
quantum processor that realises arbitrary unitary transformations on two
qubits, which are stored in trapped atomic ions. Using quantum state and
process tomography, we characterise the fidelity of our implementation for 160
randomly chosen operations. This universal control is equivalent to simulating
any pairwise interaction between spin-1/2 systems. A programmable multi-qubit
register could form a core component of a large-scale quantum processor, and
the methods used here are suitable for such a device.Comment: 7 pages, 4 figure
General framework for estimating the ultimate precision limit in noisy quantum-enhanced metrology
The estimation of parameters characterizing dynamical processes is central to
science and technology. The estimation error changes with the number N of
resources employed in the experiment (which could quantify, for instance, the
number of probes or the probing energy). Typically, it scales as 1/N^(1/2).
Quantum strategies may improve the precision, for noiseless processes, by an
extra factor 1/N^(1/2). For noisy processes, it is not known in general if and
when this improvement can be achieved. Here we propose a general framework for
obtaining attainable and useful lower bounds for the ultimate limit of
precision in noisy systems. We apply this bound to lossy optical interferometry
and atomic spectroscopy in the presence of dephasing, showing that it captures
the main features of the transition from the 1/N to the 1/N^(1/2) behaviour as
N increases, independently of the initial state of the probes, and even with
use of adaptive feedback.Comment: Published in Nature Physics. This is the revised submitted version.
The supplementary material can be found at
http://www.nature.com/nphys/journal/v7/n5/extref/nphys1958-s1.pd
A Twist in the Dyon Partition Function
In four dimensional string theories with N=4 and N=8 supersymmetries one can
often define twisted index in a subspace of the moduli space which captures
additional information on the partition function than the ones contained in the
usual helicity trace index. We compute several such indices in type IIB string
theory on K3 x T^2 and T^6, and find that they share many properties with the
usual helicity trace index that captures the spectrum of quarter BPS states in
N=4 supersymmetric string theories. In particular the partition function is a
modular form of a subgroup of Sp(2,Z) and the jumps across the walls of
marginal stability are controlled by the residues at the poles of the partition
function. However for large charges the logarithm of this index grows as 1/n
times the entropy of a black hole carrying the same charges where n is the
order of the symmetry generator that is used to define the twisted index. We
provide a macroscopic explanation of this phenomenon using quantum entropy
function formalism. The leading saddle point corresponding to the attractor
geometry fails to contribute to the twisted index, but a Z_n orbifold of the
attractor geometry produces the desired contribution.Comment: LaTeX file, 35 pages; v2: references adde
F-theory and Neutrinos: Kaluza-Klein Dilution of Flavor Hierarchy
We study minimal implementations of Majorana and Dirac neutrino scenarios in
F-theory GUT models. In both cases the mass scale of the neutrinos m_nu ~
(M_weak)^2/M_UV arises from integrating out Kaluza-Klein modes, where M_UV is
close to the GUT scale. The participation of non-holomorphic Kaluza-Klein mode
wave functions dilutes the mass hierarchy in comparison to the quark and
charged lepton sectors, in agreement with experimentally measured mass
splittings. The neutrinos are predicted to exhibit a "normal" mass hierarchy,
with masses m_3,m_2,m_1 ~ .05*(1,(alpha_GUT)^(1/2),alpha_GUT) eV. When the
interactions of the neutrino and charged lepton sectors geometrically unify,
the neutrino mixing matrix exhibits a mild hierarchical structure such that the
mixing angles theta_23 and theta_12 are large and comparable, while theta_13 is
expected to be smaller and close to the Cabibbo angle: theta_13 ~ theta_C ~
(alpha_GUT)^(1/2) ~ 0.2. This suggests that theta_13 should be near the current
experimental upper bound.Comment: v2: 83 pages, 10 figures, references adde
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