7,366 research outputs found
A Characterisation of the Weylian Structure of Space-Time by Means of Low Velocity Tests
The compatibility axiom in Ehlers, Pirani and Schild's (EPS) constructive
axiomatics of the space-time geometry that uses light rays and freely falling
particles with high velocity, is replaced by several constructions with low
velocity particles only. For that purpose we describe in a space-time with a
conformal structure and an arbitrary path structure the radial acceleration, a
Coriolis acceleration and the zig-zag construction. Each of these quantities
give effects whose requirement to vanish can be taken as alternative version of
the compatibility axiom of EPS. The procedural advantage lies in the fact, that
one can make null-experiments and that one only needs low velocity particles to
test the compatibility axiom. We show in addition that Perlick's standard clock
can exist in a Weyl space only.Comment: to appear in Gen.Rel.Gra
Kondo effect and channel mixing in oscillating molecules
We investigate the electronic transport through a molecule in the Kondo
regime. The tunneling between the electrode and the molecule is asymmetrically
modulated by the oscillations of the molecule, i.e., if the molecule gets
closer to one of the electrodes the tunneling to that electrode will increase
while for the other electrode it will decrease. The system is described by a
two-channel Anderson model with phonon-assisted hybridization, which is solved
with the Wilson numerical renormalization group method. The results for several
functional forms of tunneling modulation are presented. For a linearized
modulation the Kondo screening of the molecular spin is caused by the even or
odd conduction channel. At the critical value of the electron-phonon coupling
an unstable two-channel Kondo fixed point is found. For a realistic modulation
the spin at the molecular orbital is Kondo screened by the even conduction
channel even in the regime of strong coupling. A universal consequence of the
electron-phonon coupling is the softening of the phonon mode and the related
instability to perturbations that break the left-right symmetry. When the
frequency of oscillations decreases below the magnitude of such perturbation,
the molecule is abruptly attracted to one of the electrodes. In this regime,
the Kondo temperature is enhanced and, simultaneously, the conductance through
the molecule is suppressed.Comment: published versio
Fate of the false monopoles: induced vacuum decay
We study a gauge theory model where there is an intermediate symmetry
breaking to a meta- stable vacuum that breaks a simple gauge group to a U (1)
factor. Such models admit the existence of meta-stable magnetic monopoles,
which we dub false monopoles. We prove the existence of these monopoles in the
thin wall approximation. We determine the instantons for the collective
coordinate that corresponds to the radius of the monopole wall and we calculate
the semi-classical tunneling rate for the decay of these monopoles. The
monopole decay consequently triggers the decay of the false vacuum. As the
monopole mass is increased, we find an enhanced rate of decay of the false
vacuum relative to the celebrated homogeneous tunneling rate due to Coleman
[1].Comment: 10 pages, 4 figure
Personhood, consciousness, and god : how to be a proper pantheist
© Springer Nature B.V. 2018In this paper I develop a theory of personhood which leaves open the possibility of construing the universe as a person. If successful, it removes one bar to endorsing pantheism. I do this by examining a rising school of thought on personhood, on which persons, or selves, are understood as identical to episodes of consciousness. Through a critique of this experiential approach to personhood, I develop a theory of self as constituted of qualitative mental contents, but where these contents are also capable of unconscious existence. On this theory, though we can be conscious of our selves, consciousness turns out to be inessential to personhood. This move, I then argue, provides resources for responding to the pantheist’s problem of God’s person.Peer reviewedFinal Accepted Versio
Lattice Theories with Nonlinearly Realized Chiral Symmetry
We present the lattice formulation of effective Lagrangians in which chiral
symmetry is realized nonlinearly on the fermion fields. In this framework both
the Wilson term removing unphysical doubler fermions and the fermion mass term
do not break chiral symmetry. Our lattice formulation allows us to address
non-perturbative questions in effective theories of baryons interacting with
pions and in models involving constitutent quarks interacting with pions and
gluons. With the presented methods, a system containing a non-zero density of
static baryons interacting with pions can be studied on the lattice without
encountering a complex action problem. This might lead to new insights into the
phase diagram of strongly interacting matter at non-zero chemical potential.Comment: 3 pages, Lattice2003(chiral
Stabilized Singlets in Supergravity as a Source of the mu-parameter
Within the context of supergravity-coupled supersymmetry, fields which are
gauge and global singlets are usually considered anathema. Their vacuum
expectation values are shifted by quadratically divergent tadpole diagrams
which are cutoff at the Planck scale, destabilizing the classical potential and
driving the singlet field to large values. We demonstrate a new and generic
mechanism which stabilizes the singlet in the presence of an extended gauge
symmetry. Such a symmetry will be broken down to the Standard Model by the
supergravity interactions near the scale of spontaneous supersymmetry-breaking
in the hidden-sector (about 10^{10-11} GeV). The resulting singlet expectation
value is stabilized and naturally of order the gravitino mass, providing
therefore a weak-scale mass for the Higgs fields of the supersymmetric Standard
Model (a "mu-parameter"). The resulting low-energy theory is the minimal
supersymmetric Standard Model, with all new fields decoupling at the
intermediate scale.Comment: 9 pages, LaTe
Quantum Necking in Stressed Metallic Nanowires
When a macroscopic metallic wire is subject to tensile stress, it necks down
smoothly as it elongates. We show that nanowires with radii comparable to the
Fermi wavelength display remarkably different behavior. Using concepts from
fluid dynamics, a PDE for nanowire shape evolution is derived from a
semiclassical energy functional that includes electron-shell effects. A rich
dynamics involving movement and interaction of kinks connecting locally stable
radii is found, and a new class of universal equilibrium shapes is predicted.Comment: 4 pages, 3 postscript figures. New result on universal equilibrium
shape
Linear independence of Gamma values in positive characteristic
We investigate the arithmetic nature of special values of Thakur's function
field Gamma function at rational points. Our main result is that all linear
independence relations over the field of algebraic functions are consequences
of the known relations of Anderson and Thakur arising from the functional
equations of the Gamma function.Comment: 51 page
Physical mechanisms generating spontaneous symmetry breaking and a hierarchy of scales
We discuss the phase transition in 3+1 dimensional lambda Phi^4 theory from a
very physical perspective. The particles of the symmetric phase (`phions')
interact via a hard-core repulsion and an induced, long-range -1/r^3
attraction. If the phion mass is sufficiently small, the lowest-energy state is
not the `empty' state with no phions, but is a state with a non-zero density of
phions Bose-Einstein condensed in the zero-momentum mode. The condensate
corresponds to the spontaneous-symmetry-breaking vacuum with neq 0 and
its excitations ("phonons" in atomic-physics language) correspond to Higgs
particles. The phase transition happens when the phion's physical mass m is
still positive; it does not wait until m^2 passes through zero and becomes
negative. However, at and near the phase transition, m is much, much less than
the Higgs mass M_h. This interesting physics coexists with `triviality;' all
scattering amplitudes vanish in the continuum limit, but the vacuum condensate
becomes infinitely dense. The ratio m/M_h, which goes to zero in the continuum
limit, can be viewed as a measure of non-locality in the regularized theory. An
intricate hierarchy of length scales naturally arises. We speculate about the
possible implications of these ideas for gravity and inflation.Comment: 27 pages plus 2 files of figure
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