2,275 research outputs found
Perfect Actions with Chemical Potential
We show how to include a chemical potential \mu in perfect lattice actions.
It turns out that the standard procedure of multiplying the quark fields \Psi,
\bar\Psi at Euclidean time t by \exp(\pm \mu t), respectively, is perfect. As
an example, the case of free fermions with chemical potential is worked out
explicitly. Even after truncation, cut-off effects in the pressure and the
baryon density are small. Using a (quasi-)perfect action, numerical QCD
simulations for non-zero chemical potential become more powerful, because
coarse lattices are sufficient for extracting continuum physics.Comment: 10 pages, LaTex, 3 figure
Perfect Lattice Actions with and without Chiral Symmetry
We use perturbation theory to construct perfect lattice actions for fermions
and gauge fields by blocking directly from the continuum. When one uses a
renormalization group transformation that preserves chiral symmetry the
resulting lattice action for massless fermions is chirally symmetric but
nonlocal. When the renormalization group transformation breaks chiral symmetry,
the lattice action becomes local but chiral symmetry is explicitly broken. In
particular, starting with a chiral gauge theory in the continuum one either
obtains a lattice theory which is gauge invariant but nonlocal, or a local
theory with explicitly broken gauge invariance. In both cases the spectrum of
the lattice theory is identical with the one of the continuum and the anomaly
is correctly reproduced. We also apply our techniques to vector-like theories.
In particular we propose a new renormalization group transformation for QCD and
we optimize its parameters for locality of the perfect action.Comment: LaTex, 8 pages, Contribution to Lattice 95; Some minor typing errors
are correcte
Fixed Point Actions for Lattice Fermions
The fixed point actions for Wilson and staggered lattice fermions are
determined by iterating renormalization group transformations. In both cases a
line of fixed points is found. Some points have very local fixed point actions.
They can be used to construct perfect lattice actions for asymptotically free
fermionic theories like QCD or the Gross-Neveu model. The local fixed point
actions for Wilson fermions break chiral symmetry, while in the staggered case
the remnant symmetry is preserved. In addition, for
Wilson fermions a nonlocal fixed point is found that corresponds to free chiral
fermions. The vicinity of this fixed point is studied in the Gross-Neveu model
using perturbation theory.Comment: 6 pages, figures 1 and 4 included, figures 2,3,5,6,7 can be obtained
from [email protected]
Blackbody radiation shift in a 43Ca+ ion optical frequency standard
Motivated by the prospect of an optical frequency standard based on 43Ca+, we
calculate the blackbody radiation (BBR) shift of the 4s_1/2-3d_5/2 clock
transition, which is a major component of the uncertainty budget. The
calculations are based on the relativistic all-order single-double method where
all single and double excitations of the Dirac-Fock wave function are included
to all orders of perturbation theory. Additional calculations are conducted for
the dominant contributions in order to evaluate some omitted high-order
corrections and estimate the uncertainties of the final results. The BBR shift
obtained for this transition is 0.38(1) Hz. The tensor polarizability of the
3d_5/2 level is also calculated and its uncertainty is evaluated as well. Our
results are compared with other calculations.Comment: 4 page
Examining the Continuity between Life and Mind: Is There a Continuity between Autopoietic Intentionality and Representationality?
A weak version of the life-mind continuity thesis entails that every living system also has a basic mind (with a non-representational form of intentionality). The strong version entails that the same concepts that are sufficient to explain basic minds (with non-representational states) are also central to understanding non-basic minds (with representational states). We argue that recent work on the free energy principle supports the following claims with respect to the life-mind continuity thesis: (i) there is a strong continuity between life and mind; (ii) all living systems can be described as if they had representational states; (iii) the ’as-if representationality’ entailed by the free energy principle is central to understanding both basic forms of intentionality and intentionality in non-basic minds. In addition to this, we argue that the free energy principle also renders realism about computation and representation compatible with a strong life-mind continuity thesis (although the free energy principle does not entail computational and representational realism). In particular, we show how representationality proper can be grounded in ’as-if representationality’
AI ethics in computational psychiatry: From the neuroscience of consciousness to the ethics of consciousness
Methods used in artificial intelligence (AI) overlap with methods used in computational psychiatry (CP). Hence, considerations from AI ethics are also relevant to ethical discussions of CP. Ethical issues include, among others, fairness and data ownership and protection. Apart from this, morally relevant issues also include potential transformative effects of applications of AI—for instance, with respect to how we conceive of autonomy and privacy. Similarly, successful applications of CP may have transformative effects on how we categorise and classify mental disorders and mental health. Since many mental disorders go along with disturbed conscious experiences, it is desirable that successful applications of CP improve our understanding of disorders involving disruptions in conscious experience. Here, we discuss prospects and pitfalls of transformative effects that CP may have on our understanding of mental disorders. In particular, we examine the concern that even successful applications of CP may fail to take all aspects of disordered conscious experiences into account
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