2,028 research outputs found
The kernel of Dirac operators on and
In this paper we describe an intrinsically geometric way of producing
magnetic fields on and for which the corresponding Dirac
operators have a non-trivial kernel. In many cases we are able to compute the
dimension of the kernel. In particular we can give examples where the kernel
has any given dimension. This generalizes the examples of Loss and Yau (Commun.
Math. Phys. 104 (1986) 283-290).Comment: 51 page
Underscreened Kondo effect in quantum dots coupled to ferromagnetic leads
We analyze the equilibrium transport properties of underscreened Kondo effect
in the case of a two-level quantum dot coupled to ferromagnetic leads. Using
the numerical renormalization group (NRG) method, we have determined the gate
voltage dependence of the dot's spin and level-resolved spectral functions. We
have shown that the polarization of the dot is very susceptible to spin
imbalance in the leads and changes sign in the middle of the S=1 Coulomb
valley. Furthermore, we have also found that by fine-tuning an external
magnetic field one can compensate for the presence of ferromagnetic leads and
restore the Kondo effect in the case of Coulomb valley. However, the
underscreened Kondo effect cannot be fully recovered due to its extreme
sensitivity with respect to the magnetic field.Comment: 7 pages, 6 figure
Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
With seven planets, the TRAPPIST-1 system has the largest number of
exoplanets discovered in a single system so far. The system is of
astrobiological interest, because three of its planets orbit in the habitable
zone of the ultracool M dwarf. Assuming the planets are composed of
non-compressible iron, rock, and HO, we determine possible interior
structures for each planet. To determine how much tidal heat may be dissipated
within each planet, we construct a tidal heat generation model using a single
uniform viscosity and rigidity for each planet based on the planet's
composition. With the exception of TRAPPIST-1c, all seven of the planets have
densities low enough to indicate the presence of significant HO in some
form. Planets b and c experience enough heating from planetary tides to
maintain magma oceans in their rock mantles; planet c may have eruptions of
silicate magma on its surface, which may be detectable with next-generation
instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are
still twenty times higher than Earth's mean heat flow. Planets d and e are the
most likely to be habitable. Planet d avoids the runaway greenhouse state if
its albedo is 0.3. Determining the planet's masses within
to 0.5 Earth masses would confirm or rule out the presence of HO and/or
iron in each planet, and permit detailed models of heat production and
transport in each planet. Understanding the geodynamics of ice-rich planets f,
g, and h requires more sophisticated modeling that can self-consistently
balance heat production and transport in both rock and ice layers.Comment: 34 pages, 3 tables, 4 figures. Accepted for publication in Astronomy
& Astrophysics -- final version including corrections made in proof stag
Kondo "underscreening" cloud: spin-spin correlations around a partially screened magnetic impurity
We consider the spatial spin correlations around a partially screened spin-1
magnetic moment in a metal exhibiting the underscreened Kondo effect. We find
that the underscreening of the impurity spin results in spatial spin
correlations that are more pronounced as compared to the fully screened Kondo
effect; their power-law decay is weaker because of characteristic logarithmic
corrections at large distances. The spin correlator also changes sign as a
function of distance to the impurity allowing for ferromagnetic correlations
between conduction electron spin density and the local moment. The numerical
findings are shown to be in agreement with the predictions deriving from an
effective ferromagnetic Kondo Hamiltonian.Comment: 4+ pages, 2 figures, submitted to Phys. Rev.
Kondo screening cloud in a one dimensional wire: Numerical renormalization group study
We study the Kondo model --a magnetic impurity coupled to a one dimensional
wire via exchange coupling-- by using Wilson's numerical renormalization group
(NRG) technique. By applying an approach similar to which was used to compute
the two impurity problem we managed to improve the bad spatial resolution of
the numerical renormalization group method. In this way we have calculated the
impurity spin - conduction electron spin correlation function which is a
measure of the Kondo compensation cloud whose existence has been a long
standing problem in solid state physics. We also present results on the
temperature dependence of the Kondo correlations.Comment: published versio
New results and perspectives on R_{AA} measurements below 20 GeV CM-energy at fixed target machines
Transverse momentum spectra of pi^{+/-} at midrapidity are measured at high
p_T in p+p and p+Pb collisions at 158 GeV/nucleon beam energy by the NA49
experiment. This study is complementary to our previous results on the same
spectra from Pb+Pb collisions. The nuclear modification factors R_{A+A/p+p},
R_{p+A/p+p} and R_{A+A/p+A} as a function of p_T are extracted and compared to
RHIC measurements, thus providing insight into the energy dependence of nuclear
modification. The modification factor R_{A+A/p+A} proved to be consistent with
our previous results on the central to peripheral modification factor R_{CP}.
The limitation of our current p_T range is discussed and planned future
upgrades are outlined. Some aspects of the FAIR-CBM experiment are also
presented as a natural future continuation of the measurements at very high
p_T.Comment: Proceedings of Quark Matter 200
Is Quantum Mechanics Compatible with a Deterministic Universe? Two Interpretations of Quantum Probabilities
Two problems will be considered: the question of hidden parameters and the
problem of Kolmogorovity of quantum probabilities. Both of them will be
analyzed from the point of view of two distinct understandings of quantum
mechanical probabilities. Our analysis will be focused, as a particular
example, on the Aspect-type EPR experiment. It will be shown that the quantum
mechanical probabilities appearing in this experiment can be consistently
understood as conditional probabilities without any paradoxical consequences.
Therefore, nothing implies in the Aspect experiment that quantum theory is
incompatible with a deterministic universe.Comment: REVISED VERSION! ONLY SMALL CHANGES IN THE TEXT! compressed and
uuencoded postscript, a uuencoded version of a demo program file (epr.exe for
DOS) is attached as a "Figure
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