1,287 research outputs found
Ethical, cultural, social and individual considerations prior to transition to limitation or withdrawal of life-sustaining therapies
Understanding the Random Displacement Model: From Ground-State Properties to Localization
We give a detailed survey of results obtained in the most recent half decade
which led to a deeper understanding of the random displacement model, a model
of a random Schr\"odinger operator which describes the quantum mechanics of an
electron in a structurally disordered medium. These results started by
identifying configurations which characterize minimal energy, then led to
Lifshitz tail bounds on the integrated density of states as well as a Wegner
estimate near the spectral minimum, which ultimately resulted in a proof of
spectral and dynamical localization at low energy for the multi-dimensional
random displacement model.Comment: 31 pages, 7 figures, final version, to appear in Proceedings of
"Spectral Days 2010", Santiago, Chile, September 20-24, 201
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
Holographic Approach to Regge Trajectory and Rotating D5 brane
We study the Regge trajectories of holographic mesons and baryons by
considering rotating strings and D5 brane, which is introduced as the baryon
vertex. Our model is based on the type IIB superstring theory with the
background of asymptotic . This background is dual to a
confining supersymmetric Yang-Mills theory (SYM) with gauge condensate,
, which determines the tension of the linear potential between the quark
and anti-quark. Then the slope of the meson trajectory () is given
by this condensate as at large spin . This
relation is compatible with the other theoretical results and experiments. For
the baryon, we show the importance of spinning baryon vertex to obtain a Regge
slope compatible with the one of and series. In both cases, mesons
and baryons, the trajectories are shifted to large mass side with the same
slope for increasing current quark mass.Comment: 28 pages, 7 figure
Physical Response Functions of Strongly Coupled Massive Quantum Liquids
We study physical properties of strongly coupled massive quantum liquids from
their spectral functions using the AdS/CFT correspondence. The generic model
that we consider is dense, heavy fundamental matter coupled to SU(N_c) super
Yang-Mills theory at finite temperature above the deconfinement phase
transition but below the scale set by the baryon number density. In this setup,
we study the current-current correlators of the baryon number density using new
techniques that employ a scaling behavior in the dual geometry. Our results,
the AC conductivity, the quasi-particle spectrum and the Drude-limit parameters
like the relaxation time are simple temperature-independent expressions that
depend only on the mass-squared to density ratio and display a crossover
between a baryon- and meson-dominated regime. We concentrated on the
(2+1)-dimensional defect case, but in principle our results can also be
generalized straightforwardly to other cases.Comment: 21 pages, 10 figures, extra paragraph and figure are added in
response to referee's comment
Rigidity of SU(2,2|2)-symmetric solutions in Type IIB
We investigate the existence of half-BPS solutions in Type IIB supergravity
which are invariant under the superalgebra SU(2,2|2) realized on either AdS_5 x
S^2 x S^1 or AdS_5 x S^3 warped over a Riemann surface \Sigma with boundary. We
prove that, in both cases, the only solution is AdS_5 x S^5 itself. We argue
that this result provides evidence for the non-existence of fully back-reacted
intersecting D3/D7 branes with either AdS_5 x S^2 x S^1 x \Sigma or AdS_5 x S^3
x \Sigma near-horizon limits.Comment: 55 page
Complementary cooperation, minimal winning coalitions, and power indices
We introduce a new simple game, which is referred to as the complementary
weighted multiple majority game (C-WMMG for short). C-WMMG models a basic
cooperation rule, the complementary cooperation rule, and can be taken as a
sister model of the famous weighted majority game (WMG for short). In this
paper, we concentrate on the two dimensional C-WMMG. An interesting property of
this case is that there are at most minimal winning coalitions (MWC for
short), and they can be enumerated in time , where is the
number of players. This property guarantees that the two dimensional C-WMMG is
more handleable than WMG. In particular, we prove that the main power indices,
i.e. the Shapley-Shubik index, the Penrose-Banzhaf index, the Holler-Packel
index, and the Deegan-Packel index, are all polynomially computable. To make a
comparison with WMG, we know that it may have exponentially many MWCs, and none
of the four power indices is polynomially computable (unless P=NP). Still for
the two dimensional case, we show that local monotonicity holds for all of the
four power indices. In WMG, this property is possessed by the Shapley-Shubik
index and the Penrose-Banzhaf index, but not by the Holler-Packel index or the
Deegan-Packel index. Since our model fits very well the cooperation and
competition in team sports, we hope that it can be potentially applied in
measuring the values of players in team sports, say help people give more
objective ranking of NBA players and select MVPs, and consequently bring new
insights into contest theory and the more general field of sports economics. It
may also provide some interesting enlightenments into the design of
non-additive voting mechanisms. Last but not least, the threshold version of
C-WMMG is a generalization of WMG, and natural variants of it are closely
related with the famous airport game and the stable marriage/roommates problem.Comment: 60 page
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
Holographic Roberge-Weiss Transitions
We investigate N=4 SYM coupled to fundamental flavours at nonzero imaginary
quark chemical potential in the strong coupling and large N limit, using
gauge/gravity duality applied to the D3-D7 system, treating flavours in the
probe approximation. The interplay between Z(N) symmetry and the imaginary
chemical potential yields a series of first-order Roberge-Weiss transitions. An
additional thermal transition separates phases where quarks are bound/unbound
into mesons. This results in a set of Roberge-Weiss endpoints: we establish
that these are triple points, determine the Roberge-Weiss temperature, give the
curvature of the phase boundaries and confirm that the theory is analytic in
mu^2 when mu^2~0.Comment: 37 pages, 13 figures; minor comments added, to appear in JHE
Pion and Vector Meson Form Factors in the Kuperstein-Sonnenschein holographic model
We study phenomenological aspects of the holographic model of chiral symmetry
breaking recently introduced by Kuperstein and Sonnenschein (KS). As a first
step, we calculate the spectrum of vector and axial-vector mesons in the KS
model. We numerically compute various coupling constants of the mesons and
pions. Our analysis indicates that vector meson dominance is realized in this
model. The pion, vector meson and axial-vector meson form factors are obtained
and studied in detail. We find good agreement with QCD results. In particular,
the pion form factor closely matches available experimental data.Comment: v1: 27 pages, 9 figures, 4 tables; v2: minor changes, added more
general discussion of vector meson dominance; v3: minor changes and
additions, version accepted for publication in JHE
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