5,573 research outputs found
Renormalized QCD-inspired model for the pion and mesons
We apply the subtraction method to an effective QCD-inspired model, which
includes the Coulomb plus a zero-range hyperfine interactions, to define a
renormalized Hamiltonian for mesons. The spectrum of the renormalized
Hamiltonian agrees with the one obtained with a smeared hyperfine interaction.
The masses of the low-lying pseudo scalar and vector mesons are reasonably
described within the model.Comment: 5 pages, 3 figures, 5 references. To be published in Nucl. Phys. B
(Proc. Suppl.) Talk presented at the Workshop "Light-cone Physics: Particles
and Strings" at ECT* in Trento, Sep 3-11, 200
Transient effects on electron spin observation
In an earlier publication we addressed the problem of splitting an electron beam in the Stern-Gerlach experiment. In contrast to arguments put forward in the early days of quantum theory, we concluded that there are no issues of principle preventing the observation of electron spin during free flight. In that paper, however, we considered only a sudden switch off of the separating magnetic field. In this work we consider the possible effects of finite switching times at the beginning and the end of the interaction period. We consider a model where the coupling between the electron and the field is time dependent. As a result of the time dependence, the field also acquires an electric component, but this seems to cause no significant change of our conclusions. On the other hand, the smooth change of the interaction enforces the same longitudinal velocity on the electron both at the beginning and end of the interaction period because of conservation laws; this effect was missing in our earlier calculations. As the electrons are supposed to travel as a beam, this feature helps by restoring the beam quality after the interaction
Uncertainty and stepwise investment
We analyze the optimal investment strategy of a firm that can complete a project either in one stage at a single freely chosen time point or in incremental steps at distinct time points. The presence of economies of scale gives rise to the following trade-off: lumpy investment has a lower total cost, but stepwise investment gives more flexibility by letting the firm choose the timing individually for each stage. Our main question is how uncertainty in market development affects this trade-off. The answer is unambiguous and in contrast with a conventional real-options intuition: higher uncertainty makes the single-stage investment more attractive relative to the more flexible stepwise investment strategy
Renormalization of an effective Light-Cone QCD-inspired theory for the Pion and other Mesons
The renormalization of the effective QCD-Hamiltonian theory for the
quark-antiquark channel is performed in terms of a renormalized or fixed-point
Hamiltonian that leads to subtracted dynamical equations. The fixed
point-Hamiltonian brings the renormalization conditions as well as the
counterterms that render the theory finite. The approach is renormalization
group invariant. The parameters of the renormalized effective QCD-Hamiltonian
comes from the pion mass and radius, for a given constituent quark mass. The 1s
and excited 2s states of are calculated as a function of the mass of
the quark being s, c or b, and compared to the experimental values.Comment: 39 pages, 10 figure
Finiteness Conditions for Light-Front Hamiltonians
In the context of simple models, it is shown that demanding finiteness for
physical masses with respect to a longitudinal cutoff, can be used to fix the
ambiguity in the renormalization of fermions masses in the Hamiltonian
light-front formulation. Difficulties that arise in applications of finiteness
conditions to discrete light-cone quantization are discussed.Comment: REVTEX, 9 page
A data-driven approach to the automated study of cross-species homologies
Behavioral neuroscience has made great strides in developing animal models of human behavior and psychiatric disorders. Animal models allow for the formulation of hypotheses regarding the mechanisms underlying psychiatric disorders, and the opportunity to test these hypotheses using procedures that are too invasive for human participants. However, recent scientific reviews have highlighted the low success rate of translating results from animal models into clinical interventions in humans. A potential roadblock is that bidirectional functional mappings between the human and rodent brain are incomplete. To narrow this gap, we created a framework, Neurobabel, for performing large-scale automated synthesis of human neuroimaging data and behavioral neuroscience data. By leveraging the semantics of how researchers within each field describe their studies, this framework enables region to region mapping of brain regions across species, as well as cross-species mapping of psychological functions. As a proof of concept, we utilize the framework to create a functional cross-species mapping between the amygdala and hippocampus for fear-related and spatial memories, respectively. We then proceed to address two open questions in the field: (1) Do rodents have a dorsolateral prefrontal cortex? (2) Which human brain region corresponds to the rodent prelimbic cortex
Tube Model for Light-Front QCD
We propose the tube model as a first step in solving the bound state problem
in light-front QCD. In this approach we neglect transverse variations of the
fields, producing a model with 1+1 dimensional dynamics. We then solve the two,
three, and four particle sectors of the model for the case of pure glue SU(3).
We study convergence to the continuum limit and various properties of the
spectrum.Comment: 29 page
Cryptococcosis in the Dog
A 10-month-old German Shorthair female dog was admitted to Stange Memorial Veterinary Clinic on August 18, 1970, with a history of periodic depression and coughing for one month. The animal had responded to previous cortoicosteroid treatment. A more detailed history and physical examination revealed a reoccurring conjunctivitis and photophobia
Noncommutative Gauge Theory on the q-Deformed Euclidean Plane
In this talk we recall some concepts of Noncommutative Gauge Theories. In
particular, we discuss the q-deformed two-dimensional Euclidean Plane which is
covariant with respect to the q-deformed Euclidean group. A Seiberg-Witten map
is constructed to express noncommutative fields in terms of their commutative
counterparts.Comment: 5 pages; Talk given by Frank Meyer at the 9th Adriatic Meeting,
September 4th-14th, 2003, Dubrovni
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