4,173 research outputs found
Renormalization Group and Dynamics of Supersymmetric Gauge Theories
We discuss questions related to renormalization group and to nonperturbative
aspects of non-Abelian gauge theories with N=2 and/or N=1 supersymmetry.
Results on perturbative and nonperturbative functions of these theories
are reviewed, and new mechanisms of confinement and dynamical symmetry breaking
recently found in a class of , and theories are
discussed.Comment: 13 pages, 3 figures, uses ws-p9-75x6-50.cls. Lecture given at the
Second Conference on the ERG, Rome 200
The dihadron fragmentation function and its evolution
Dihadron fragmentation functions and their evolution are studied in the
process of annihilation. Under the collinear factorization
approximation and facilitated by the cut-vertex technique, the two hadron
inclusive cross section at leading order (LO) is shown to factorize into a
short distance parton cross section and a long distance dihadron fragmentation
function. We provide the definition of such a dihadron fragmentation function
in terms of parton matrix elements and derive its DGLAP evolution equation at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: 27 pages, 2 column, Revtex4, 21 figure
Sp(N) higher-derivative F-terms via singular superpotentials
We generalize the higher-derivative F-terms introduced by Beasley and Witten
(hep-th/0409149) for SU(2) superQCD to Sp(N) gauge theories with fundamental
matter. We generate these terms by integrating out massive modes at tree level
from an effective superpotential on the chiral ring of the microscopic theory.
Though this superpotential is singular, its singularities are mild enough to
permit the unambiguous identification of its minima, and gives sensible answers
upon integrating out massive modes near any given minimum.Comment: 15 pages, 6 figure
On singular effective superpotentials in supersymmetric gauge theories
We study N=1 supersymmetric SU(2) gauge theory in four dimensions with a
large number of massless quarks. We argue that effective superpotentials as a
function of local gauge-invariant chiral fields should exist for these
theories. We show that although the superpotentials are singular, they
nevertheless correctly describe the moduli space of vacua, are consistent under
RG flow to fewer flavors upon turning on masses, and also reproduce by a
tree-level calculation the higher-derivative F-terms calculated by Beasely and
Witten (hep-th/0409149) using instanton methods. We note that this phenomenon
can also occur in supersymmetric gauge theories in various dimensions.Comment: 21 pages, 5 figures; minor errors correcte
Topological-charge anomalies in supersymmetric theories with domain walls
Domain walls in 1+2 dimensions are studied to clarify some general features
of topological-charge anomalies in supersymmetric theories, by extensive use of
a superfield supercurrent. For domain walls quantum modifications of the
supercharge algebra arise not only from the short-distance anomaly but also
from another source of long-distance origin, induced spin in the domain-wall
background, and the latter dominates in the sum. A close look into the
supersymmetric trace identity, which naturally accommodates the central-charge
anomaly and its superpartners, shows an interesting consequence of the
improvement of the supercurrent: Via an improvement the anomaly in the central
charge can be transferred from induced spin in the fermion sector to an induced
potential in the boson sector. This fact reveals a dual character, both
fermionic and bosonic, of the central-charge anomaly, which reflects the
underlying supersymmetry. The one-loop superfield effective action is also
constructed to verify the anomaly and BPS saturation of the domain-wall
spectrum.Comment: 8 pages, Revte
Halcyornis toliapicus (aves: Lower Eocene, England) indicates advanced neuromorphology in Mesozoic Neornithes
Our recent X-ray micro computer-tomographic (μCT) investigations of Prophaethon shrubsolei and Odontopteryx toliapica from the Lower Eocene London Clay Formation of England revealed the avian brain to have been essentially modern in form by 55 Ma, but that an important vision-related synapomorphy of living birds, the eminentia sagittalis of the telencephalon, was poorly developed. This evidence suggested that the feature probably appeared close to the end of the Mesozoic. Here we use μCT analysis to describe the endocranium of Halcyornis toliapicus, also from the London Clay Formation. The affinities of Halcyornis have been hotly debated, with the taxon referred to the Charadriiformes (Laridae), Coraciiformes (Alcedinidae, and its own family Halcyornithidae) and most recently that Halcyornithidae may be a possible senior synonym of Pseudasturidae (Pan-Psittaciformes). Unlike Prophaethon and Odontopteryx, the eminentia sagittalis of Halcyornis is strongly developed and comparable to that of living species. Like those London Clay taxa, the eminentia sagittalis occupies a rostral position on the telencephalon. The senses of Halcyornis appear to have been well developed. The length of the cochlear duct of the inner ear indicates a hearing sensitivity within the upper range of living species, and enlarged olfactory lobes suggest a reasonable reliance on sense of smell. The optic nerves were especially well developed which, together with the strong development of the eminentia sagittalis, indicates a high degree of visual specialization in Halcyornis. The advanced development of the eminentia sagittalis further supports a Mesozoic age for the appearance of this structure and associated neural architectural complexity found in extant Aves. The eminentia sagittalis of living Psittaciformes is situated caudally on the telencephalon, making a Pan-Psittaciformes relationship unlikely for Halcyorni
Gravitino condensation in fivebrane backgrounds
We calculate the tension of the D3-brane in the fivebrane background which is
described by the exactly solvable SU(2)_k x U(1) world-sheet conformal field
theory with large Kac-Moody level k. The D3-brane tension is extracted from the
amplitude of one closed string exchange between two parallel D3-branes, and the
amplitude is calculated by utilizing the open-closed string duality. The
tension of the D3-brane in the background does not coincide with the one in the
flat space-time even in the flat space-time limit: k -> infinity. The finite
curvature effect should vanish in the flat space-time limit and only the
topological effect can remain. Therefore, the deviation indicates the
condensation of gravitino and/or dilatino which has been expected in the
fivebrane background as a gravitational instanton.Comment: 16 pages, 1 figur
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