562 research outputs found
Differential Renormalization of Massive Quantum Field Theories
We extend the method of differential renormalization to massive quantum field
theories treating in particular \ph4-theory and QED. As in the massless case,
the method proves to be simple and powerful, and we are able to find, in
particular, compact explicit coordinate space expressions for the finite parts
of two notably complicated diagrams, namely, the 2-loop 2-point function in
\ph4 and the 1-loop vertex in QED.Comment: 8 pages(LaTex, no figures
Predicting the onset of rafting of c 0 precipitates by channel deformation in a Ni superalloy
The growth or shrinkage, normal to 001, of the interfaces between the Îł matrix and cuboidal Îł' precipitates is examined for a Ni-base superalloy, by considering the force acting on the interfaces. The force is produced by the precipitate coherency misfit and the stress produced by plastic deformation in channels of the Îł matrix. A simple expression, which directly addresses the origin of the surface force, is given. The plastic deformation within the initially active Îł matrix channels exerts the force to cause rafting. The subsequent activation of other types of channels also promotes the rafting in the same direction as the first active channels, when the plastic strain of the former channels increases. These issues are also discussed in terms of analysis based on those dislocations caused by the precipitate misfit and those produced by the plastic deformation
H-Band Spectroscopic Classification of OB Stars
We present a new spectroscopic classification for OB stars based on H-band
(1.5 micron to 1.8 micron) observations of a sample of stars with optical
spectral types. Our initial sample of nine stars demonstrates that the
combination of He I 1.7002 micron and H Brackett series absorption can be used
to determine spectral types for stars between about O4 and B7 (to within about
+/- 2 sub-types). We find that the Brackett series exhibits luminosity effects
similar to the Balmer series for the B stars. This classification scheme will
be useful in studies of optically obscured high mass star forming regions. In
addition, we present spectra for the OB stars near 1.1 micron and 1.3 micron
which may be of use in analyzing their atmospheres and winds.Comment: Accepted by AJ, 16 pages Latex (aastex4.0) including 4 figures and 2
tables. A complete PostScript copy is available at
ftp://degobah.colorado.edu/pub/rblum/Hband
Light Monopoles, Electric Vortices and Instantons
The physics of the bare Seiberg-Witten action, without supersymmetric
partners, is considered in the framework of standard Quantum Field Theory. The
topological analysis related to the solutions of the Seiberg-Witten equations
is performed and the phase structure of the model is analysed.Comment: 9 pages, late
Quintics with Finite Simple Symmetries
We construct all quintic invariants in five variables with simple Non-Abelian
finite symmetry groups. These define Calabi-Yau three-folds which are left
invariant by the action of A_5, A_6 or PSL_2(11).Comment: 18 pages, typos corrected, matches published versio
What is the discrete gauge symmetry of the R-parity violating MSSM?
The lack of experimental evidence for supersymmetry motivates R-parity
violating realizations of the MSSM. Dropping R-parity, alternative symmetries
have to be imposed in order to stabilize the proton. We determine the possible
discrete R and non-R symmetries, which allow for renormalizable R-parity
violating terms in the superpotential and which, at the effective level, are
consistent with the constraints from nucleon decay. Assuming a gauge origin, we
require the symmetry to be discrete gauge anomaly-free, allowing also for
cancellation via the Green Schwarz mechanism. Furthermore, we demand lepton
number violating neutrino mass terms either at the renormalizable or
non-renormalizable level. In order to solve the mu problem, the discrete Z_N or
Z_N^R symmetries have to forbid any bilinear superpotential operator at tree
level. In the case of renormalizable baryon number violation the smallest
possible symmetry satisfying all conditions is a unique hexality Z_6^R. In the
case of renormalizable lepton number violation the smallest symmetries are two
hexalities, one Z_6 and one Z_6^R.Comment: 25 pages, version to appear in PR
Quark Mass Matrices with Four and Five Texture Zeroes, and the CKM Matrix, in terms of Mass Eigenvalues
Using the triangular matrix techniques of Kuo et al and Chiu et al for the
four and five texture zero cases, with vanishing (11) elements for U and D
matrices, it is shown, from the general eigenvalue equations and hierarchy
conditions, that the quark mass matrices, and the CKM matrix can be expressed
(except for the phases) entirely in terms of quark masses. The matrix
structures are then quite simple and transparent. We confirm their results for
the five texture zero case but find, upon closer examination of all the CKM
elements which our results provide, that six of their nine patterns for the
four texture zero case are not compatible with experiments. In total, only one
five-texture zero and three four-texture zero patterns are allowed.Comment: 15 pages, 3 table
Large Lepton Mixings from Continuous Symmetries
Within the broad context of quark-lepton unification, we investigate the
implications of broken continuous family symmetries which result from requiring
that in the limit of exact symmetry, the Dirac mass matrices yield hierarchical
masses for the quarks and charged leptons, but lead to degenerate light
neutrino masses as a consequence of the seesaw mechanism, without requiring
hierarchical right-handed neutrino mass terms. Quark mixing is then naturally
small and proportional to the size of the perturbation, but lepton mixing is
large as a result of degenerate perturbation theory, shifted from maximal
mixing by the size of the perturbation. Within this approach, we study an
illustrative two-family prototype model with an SO(2) family symmetry, and
discuss extensions to three-family models.Comment: 23 page
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