110,817 research outputs found
Interplay of Spin and Orbital Angular Momentum in the Proton
We derive the consequences of the Myhrer-Thomas explanation of the proton
spin problem for the distribution of orbital angular momentum on the valence
and sea quarks. After QCD evolution these results are found to be in very good
agreement with both recent lattice QCD calculations and the experimental
constraints from Hermes and JLab
Nucleons, Nuclear Matter and Quark Matter: A unified NJL approach
We use an effective quark model to describe both hadronic matter and
deconfined quark matter. By calculating the equations of state and the
corresponding neutron star properties, we show that the internal properties of
the nucleon have important implications for the properties of these systems.Comment: 17 pages, 5 figures, Section 5 extended, references adde
A Smooth Exit from Eternal Inflation?
The usual theory of inflation breaks down in eternal inflation. We derive a
dual description of eternal inflation in terms of a deformed Euclidean CFT
located at the threshold of eternal inflation. The partition function gives the
amplitude of different geometries of the threshold surface in the no-boundary
state. Its local and global behavior in dual toy models shows that the
amplitude is low for surfaces which are not nearly conformal to the round
three-sphere and essentially zero for surfaces with negative curvature. Based
on this we conjecture that the exit from eternal inflation does not produce an
infinite fractal-like multiverse, but is finite and reasonably smooth.Comment: 15 pages; v2: added explicit calculation of higher-spin toy-model;
v3: minor changes to provide more context, references added, version accepted
for publication in JHE
Spin and orbital angular momentum of the proton
Since the announcement of the proton spin crisis by the European Muon
Collaboration there has been considerable progress in unravelling the
distribution of spin and orbital angular momentum within the proton. We review
the current status of the problem, showing that not only have strong upper
limits have been placed on the amount of polarized glue in the proton but that
the experimental determination of the spin content has become much more
precise. It is now clear that the origin of the discrepancy between experiment
and the naive expectation of the fraction of spin carried by the quarks and
anti-quarks in the proton lies in the non-perturbative structure of the proton.
We explain how the features expected in a modern, relativistic and chirally
symmetric description of nucleon structure naturally explain the current data.
The consequences of this explanation for the presence of orbital angular
momentum on quarks and gluons is reviewed and comparison made with recent
results from lattice QCD and experimental data.Comment: Lectures at Aligarh University (4th DAE-BRNS Workshop on Hadron
Physics, Feb 18-21, 200
A New Hypothesis on the Origin of the Three Generations
We suggest that the Standard Model may undergo a supercritical transition
near the Landau scale, where the U(1) gauge boson couples to the left and right
handed states of any given fermion with different charges. This scenario
naturally gives rise to three generations of fermion, corresponding to the
three critical scales for the right-right, right-left and left-left fermion
interactions going supercritical, as well as CP violation in the quark sector.Comment: 12 pages, LaTeX, To appear in Mod.Phys.Lett.A (1996
Special Geometry and Twisted Moduli in Orbifold Theories with Continuous Wilson Lines
Target space duality symmetries, which acts on K\"ahler and continuous Wilson
line moduli, of a () 2-dimensional subspace of the moduli
space of orbifold compactification are modified to include twisted moduli.
These spaces described by the cosets are
K\"ahler, a fact which is exploited in deriving the extension of tree
level duality transformation to include higher orders of the twisted moduli.
Also, restrictions on these higher order terms are derived.Comment: 13 page
A Classification and Analysis of Higgs-flavor Models
A classification is given of Higgs-flavor models. In these models, there are
several Higgs doublets in an irreducible multiplet R_{Phi} of a non-abelian
symmetry G_{Phi}, under which the quarks and leptons do not transform (thus
giving minimal flavor-changing for the fermions). It is found that different
G_{Phi} and R_{Phi} lead to very distinctive spectra of the extra Higgs
doublets, including different numbers of "sequential Higgs" and of "inert
Higgs" that could play the role of dark matter, different mass relations, and
different patterns of SU(2)_L-breaking splittings within the Higgs doublets.Comment: 35 page
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