25,754 research outputs found
Impact Parameter Dependent Parton Distributions for a Relativistic Composite System
We investigate the impact parameter dependent parton distributions for a
relativistic composite system in light-front framework. We express them in
terms of overlaps of light-cone wave functions for a self consistent two-body
spin-1/2 state, namely an electron dressed with a photon in QED. The pdfs are
distorted in the transverse space for transverse polarization of the state at
one loop level.Comment: 4 pages, presented at Lightcone 2004, August 16-20, Amsterdam,
Netherland
Contribution from unresolved discrete sources to the Extragalactic Gamma-Ray Background (EGRB)
The origin of the extragalactic gamma-ray background (EGRB) is still an open
question, even after nearly forty years of its discovery. The emission could
originate from either truly diffuse processes or from unresolved point sources.
Although the majority of the 271 point sources detected by EGRET (Energetic
Gamma Ray Experiment Telescope) are unidentified, of the identified sources,
blazars are the dominant candidates. Therefore, unresolved blazars may be
considered the main contributor to the EGRB, and many studies have been carried
out to understand their distribution, evolution and contribution to the EGRB.
Considering that gamma-ray emission comes mostly from jets of blazars and that
the jet emission decreases rapidly with increasing jet to line-of-sight angle,
it is not surprising that EGRET was not able to detect many large inclination
angle active galactic nuclei (AGNs). Though Fermi could only detect a few large
inclination angle AGNs in the first three months' survey, it is expected to
detect many such sources in the near future. Since non-blazar AGNs are expected
to have higher density as compared to blazars, these could also contribute
significantly to the EGRB. In this paper we discuss contributions from
unresolved discrete sources including normal galaxies, starburst galaxies,
blazars and off-axis AGNs to the EGRB.Comment: 11 pages, 4 figures, accepted for publication in RA
Chiral odd GPDs in transverse and longitudinal impact parameter spaces
We investigate the chiral odd generalized parton distributions (GPDs) for
non-zero skewness in transverse and longitudinal position spaces by
taking Fourier transform with respect to the transverse and longitudinal
momentum transfer respectively. We present overlap formulas for the chiral-odd
GPDs in terms of light-front wave functions (LFWFs) of the proton both in the
ERBL and DGLAP regions. We calculate them in a field theory inspired model of a
relativistic spin 1/2 composite state with the correct correlation between the
different LFWFs in Fock space, namely that of the quantum fluctuations of an
electron in a generalized form of QED. We show the spin-orbit correlation
effect of the two-particle LFWF as well as the correlation between the
constituent spin and the transverse spin of the target.Comment: 1 figure and references added, typos corrected. version to appear in
Phys.Rev.
Reanalyzing the upper limit on the tensor-to-scalar perturbation ratio r_T in a quartic potential inflationary model
We study the polynomial chaotic inflation model with a single scalar field in
a double well quartic potential which has recently been shown to be consistent
with Planck data. In particular, we study the effects of lifting the degeneracy
between the two vacua on the inflationary observables, i.e. spectral index n_s
and tensor-to-scalar perturbation ratio r_T. We find that removing the
degeneracy allows the model to satisfy the upper limit constraints on r_T from
Planck data, provided the field starts near the local maximum. We also
calculate the scalar power spectrum and non-Gaussianity parameter f_NL for the
primordial scalar perturbations in this model.Comment: 7 pages, 7 figures; v2: discussion added, submitted to Phys. Lett. B;
v3: published versio
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