1,292 research outputs found
Anomalously light states in super-Yang-Mills Chern-Simons theory
Inspired by our previous finding that supersymmetric Yang-Mills-Chern-Simons
(SYM-CS) theory dimensionally reduced to 1+1 dimensions possesses approximate
Bogomol'nyi-Prasad-Sommerfield (BPS) states, we study the analogous phenomenon
in the three-dimensional theory. Approximate BPS states in two dimensions have
masses which are nearly independent of the Yang-Mills coupling and proportional
to their average number of partons. These states are a reflection of the
exactly massless BPS states of the underlying pure SYM theory. In three
dimensions we find that this mechanism leads to anomalously light bound states.
While the mass scale is still proportional to the average number of partons
times the square of the CS coupling, the average number of partons in these
bound states changes with the Yang-Mills coupling. Therefore, the masses of
these states are not independent of the coupling. Our numerical calculations
are done using supersymmetric discrete light-cone quantization (SDLCQ).Comment: 14 pages, 3 figures, LaTe
Van der Waals density functional: Self-consistent potential and the nature of the van der Waals bond
We derive the exchange-correlation potential corresponding to the nonlocal
van der Waals density functional [M. Dion, H. Rydberg, E. Schroder, D. C.
Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)]. We use this
potential for a self-consistent calculation of the ground state properties of a
number of van der Waals complexes as well as crystalline silicon. For the
latter, where little or no van der Waals interaction is expected, we find that
the results are mostly determined by semilocal exchange and correlation as in
standard generalized gradient approximations (GGA), with the fully nonlocal
term giving little effect. On the other hand, our results for the van der Waals
complexes show that the self-consistency has little effect at equilibrium
separations. This finding validates previous calculations with the same
functional that treated the fully nonlocal term as a post GGA perturbation. A
comparison of our results with wave-function calculations demonstrates the
usefulness of our approach. The exchange-correlation potential also allows us
to calculate Hellmann-Feynman forces, hence providing the means for efficient
geometry relaxations as well as unleashing the potential use of other standard
techniques that depend on the self-consistent charge distribution. The nature
of the van der Waals bond is discussed in terms of the self-consistent bonding
charge.Comment: submitted to Phys. Rev.
Modulation of facial mimicry by attitudes
The current experiment explored the influence of attitudes on facial reactions to emotional faces. The participantsâ attitudes (positive, neutral, and negative) towards three types of characters were manipulated by written reports. Afterwards participants saw happy, neutral, and sad facial expressions of the respective characters while their facial muscular reactions (M. Corrugator supercilii and M. Zygomaticus major) were recorded electromyografically. Results revealed facial mimicry reactions to happy and sad faces of positive characters, but less and even incongruent facial muscular reactions to happy and sad faces of negative characters. Overall, the results show that attitudes, formed in a few minutes, and only by reports and not by own experiences, can moderate automatic non-verbal social behavior, i.e. facial mimicry
Anti-Periodic Boundary Conditions in Supersymmetric DLCQ
It is of considerable importance to have a numerical method for solving
supersymmetric theories that can support a non-zero central charge. The central
charge in supersymmetric theories is in general a boundary integral and
therefore vanishes when one uses periodic boundary conditions. One is therefore
prevented from studying BPS states in the standard supersymmetric formulation
of DLCQ (SDLCQ). We present a novel formulation of SDLCQ where the fields
satisfy anti-periodic boundary conditions. The Hamiltonian is written as the
anti-commutator of two charges, as in SDLCQ. The anti-periodic SDLCQ we
consider breaks supersymmetry at finite resolution, but requires no
renormalization and becomes supersymmetric in the continuum limit. In
principle, this method could be used to study BPS states. However, we find its
convergence to be disappointingly slow.Comment: 9pp, 2 figure
Determining a quantum state by means of a single apparatus
The unknown state \hrho of a quantum system S is determined by letting it
interact with an auxiliary system A, the initial state of which is known. A
one-to-one mapping can thus be realized between the density matrix \hrho and
the probabilities of occurrence of the eigenvalues of a single and factorized
observable of S+A, so that \hrho can be determined by repeated measurements
using a single apparatus. If S and A are spins, it suffices to measure
simultaneously their -components after a controlled interaction. The most
robust setups are determined in this case, for an initially pure or a
completely disordered state of A. They involve an Ising or anisotropic
Heisenberg coupling and an external field.Comment: 5 pages revte
Simulation of Dimensionally Reduced SYM-Chern-Simons Theory
A supersymmetric formulation of a three-dimensional SYM-Chern-Simons theory
using light-cone quantization is presented, and the supercharges are calculated
in light-cone gauge. The theory is dimensionally reduced by requiring all
fields to be independent of the transverse dimension. The result is a
non-trivial two-dimensional supersymmetric theory with an adjoint scalar and an
adjoint fermion. We perform a numerical simulation of this SYM-Chern-Simons
theory in 1+1 dimensions using SDLCQ (Supersymmetric Discrete Light-Cone
Quantization). We find that the character of the bound states of this theory is
very different from previously considered two-dimensional supersymmetric gauge
theories. The low-energy bound states of this theory are very ``QCD-like.'' The
wave functions of some of the low mass states have a striking valence
structure. We present the valence and sea parton structure functions of these
states. In addition, we identify BPS-like states which are almost independent
of the coupling. Their masses are proportional to their parton number in the
large-coupling limit.Comment: 18pp. 7 figures, uses REVTe
Cardiac index monitoring by pulse contour analysis and thermodilution after pediatric cardiac surgery
ObjectivesTo validate a new device (PiCCO system; Pulsion Medical Systems, Munich, Germany), we compared cardiac index derived from transpulmonary thermodilution and from pulse contour analysis in pediatric patients after surgery for congenital heart disease. We performed a prospective clinical study in a pediatric cardiac intensive care unit of a university hospital.MethodsTwenty-four patients who had had cardiac surgery for congenital heart disease (median age 4.2 years, range 1.4-15.2 years) were investigated in the first 24 hours after admission to the intensive care unit. A 3F thermodilution catheter was inserted in the femoral artery. Intracardiac shunts were excluded by echocardiography intraoperatively or postoperatively. Cardiac index derived from pulse contour analysis was documented in each patient 1, 4, 8, 12, 16, 20, and 24 hours after admission to the intensive care unit. Subsequently, a set of three measurements of thermodilution cardiac indices derived by injections into a central venous line was performed and calculated by the PiCCO system.ResultsThe mean bias between cardiac indices derived by thermodilution and those derived by pulse contour analysis over all data points was 0.05 (SD 0.4) L · min · mâ2 (95% confidence interval 0.01-0.10). A strong correlation between thermodilution and contour analysis cardiac indices was calculated (Pearson correlation coefficient r = 0.93; coefficient of determination r2 = 0.86).ConclusionsPulse contour analysis is a suitable method to monitor cardiac index over a wide range of indices after surgery for congenital heart disease in pediatric patients. Pulse contour analysis allows online monitoring of cardiac index. The PiCCO device can be recalibrated with the integrated transpulmonary thermodilution within a short time frame
On the Spectrum of QCD(1+1) with SU(N_c) Currents
Extending previous work, we calculate in this note the fermionic spectrum of
two-dimensional QCD (QCD_2) in the formulation with SU(N_c) currents. Together
with the results in the bosonic sector this allows to address the as yet
unresolved task of finding the single-particle states of this theory as a
function of the ratio of the numbers of flavors and colors, \lambda=N_f/N_c,
anew. We construct the Hamiltonian matrix in DLCQ formulation as an algebraic
function of the harmonic resolution K and the continuous parameter \lambda.
Amongst the more surprising findings in the fermionic sector chiefly considered
here is that the fermion momentum is a function of \lambda. This dependence is
necessary in order to reproduce the well-known 't Hooft and large N_f spectra.
Remarkably, those spectra have the same single-particle content as the ones in
the bosonic sectors. The twist here is the dramatically different sizes of the
Fock bases in the two sectors, which makes it possible to interpret in
principle all states of the discrete approach. The hope is that some of this
insight carries over into the continuum. We also present some new findings
concerning the single-particle spectrum of the adjoint theory.Comment: 21 pp., 13 figures, version published in PR
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