7,577 research outputs found
The Three Loop Two-Mass Contribution to the Gluon Vacuum Polarization
We calculate the two-mass contribution to the 3-loop vacuum polarization of
the gluon in Quantum Chromodynamics at virtuality for general masses
and also present the analogous result for the photon in Quantum
Electrodynamics.Comment: 5 pages Late
The unpolarized two-loop massive pure singlet Wilson coefficients for deep-inelastic scattering
We calculate the massive two--loop pure singlet Wilson coefficients for heavy
quark production in the unpolarized case analytically in the whole kinematic
region and derive the threshold and asymptotic expansions. We also recalculate
the corresponding massless two--loop Wilson coefficients. The complete
expressions contain iterated integrals with elliptic letters. The contributing
alphabets enlarge the Kummer-Poincar\'e letters by a series of square-root
valued letters. A new class of iterated integrals, the Kummer-elliptic
integrals, are introduced. For the structure functions and we also
derive improved asymptotic representations adding power corrections. Numerical
results are presented.Comment: 42, pages Latex, 8 Figure
The Initial State QED Corrections to Annihilation to a Neutral Vector Boson Revisited
We calculate the non-singlet, the pure singlet contribution, and their
interference term, at due to electron-pair initial state
radiation to annihilation into a neutral vector boson in a direct
analytic computation without any approximation. The correction is represented
in terms of iterated incomplete elliptic integrals. Performing the limit we find discrepancies with the earlier results of
Ref.~\cite{Berends:1987ab} and confirm results obtained in
Ref.~\cite{Blumlein:2011mi} where the effective method of massive operator
matrix elements has been used, which works for all but the power corrections in
. In this way, we also confirm the validity of the factorization of
massive partons in the Drell-Yan process. We also add non-logarithmic terms at
which have not been considered in \cite{Berends:1987ab}. The
corrections are of central importance for precision analyzes in
annihilation into at high luminosity.Comment: 4 pages Latex, 2 Figures, several style file
The two-mass contribution to the three-loop pure singlet operator matrix element
We present the two-mass QCD contributions to the pure singlet operator matrix
element at three loop order in x-space. These terms are relevant for
calculating the structure function at as well as
for the matching relations in the variable flavor number scheme and the heavy
quark distribution functions at the same order. The result for the operator
matrix element is given in terms of generalized iterated integrals that include
square root letters in the alphabet, depending also on the mass ratio through
the main argument. Numerical results are presented.Comment: 28 papges Latex, 3 figure
The Two-mass Contribution to the Three-Loop Gluonic Operator Matrix Element
We calculate the two-mass QCD contributions to the massive operator matrix
element at in analytic form in Mellin
- and -space, maintaining the complete dependence on the heavy quark mass
ratio. These terms are important ingredients for the matching relations of the
variable flavor number scheme in the presence of two heavy quark flavors, such
as charm and bottom. In Mellin -space the result is given in the form of
nested harmonic, generalized harmonic, cyclotomic and binomial sums, with
arguments depending on the mass ratio. The Mellin inversion of these quantities
to -space gives rise to generalized iterated integrals with square root
valued letters in the alphabet, depending on the mass ratio as well. Numerical
results are presented.Comment: 99 pages LATEX, 2 Figure
Suzaku Reveals Helium-burning Products in the X-ray Emitting Planetary Nebula BD+303639
BD+303639, the brightest planetary nebula at X-ray energies, was observed
with Suzaku, an X-ray observatory launched on 2005 July 10. Using the X-ray
Imaging Spectrometer, the K-lines from C VI, O VII, and O VIII were resolved
for the first time, and C/O, N/O, and Ne/O abundance ratios determined. The C/O
and Ne/O abundance ratios exceed the solar value by a factor of at least 30 and
5, respectively. These results indicate that the X-rays are emitted mainly by
helium shell-burning products.Comment: 12 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
Precision Measurements of Higgs Couplings: Implications for New Physics Scales
The measured properties of the recently discovered Higgs boson are in good
agreement with predictions from the Standard Model. However, small deviations
in the Higgs couplings may manifest themselves once the currently large
uncertainties will be improved as part of the LHC program and at a future Higgs
factory. We review typical new physics scenarios that lead to observable
modifications of the Higgs interactions. They can be divided into two broad
categories: mixing effects as in portal models or extended Higgs sectors, and
vertex loop effects from new matter or gauge fields. In each model we relate
coupling deviations to their effective new physics scale. It turns out that
with percent level precision the Higgs couplings will be sensitive to the
multi-TeV regime.Comment: Invited review for Journal of Physics G, 33pp; v2: references added
and improved discussion of operator basis in section 2.
The massive 3-loop operator matrix elements with two masses and the generalized variable flavor number scheme
We report on our latest results in the calculation of the two--mass
contributions to 3--loop operator matrix elements (OMEs). These OMEs are needed
to compute the corresponding contributions to the deep-inealstic scattering
structure functions and to generalize the variable flavor number scheme by
including both charm and bottom quarks. We present the results for the
non-singlet and OMEs, and compare the size of their contribution
relative to the single mass case. Results for the gluonic OME are
given in the physical case, going beyond those presented in a previous
publication where scalar diagrams were computed. We also discuss our recently
published two--mass contribution to the pure singlet OME, and present an
alternative method of calculating the corresponding diagrams.Comment: 20 pages Latex, 5 Figures, different style file
Stacking Gravitational Wave Signals from Soft Gamma Repeater Bursts
Soft gamma repeaters (SGRs) have unique properties that make them intriguing
targets for gravitational wave (GW) searches. They are nearby, their burst
emission mechanism may involve neutron star crust fractures and excitation of
quasi-normal modes, and they burst repeatedly and sometimes spectacularly. A
recent LIGO search for transient GW from these sources placed upper limits on a
set of almost 200 individual SGR bursts. These limits were within the
theoretically predicted range of some models. We present a new search strategy
which builds upon the method used there by "stacking" potential GW signals from
multiple SGR bursts. We assume that variation in the time difference between
burst electromagnetic emission and burst GW emission is small relative to the
GW signal duration, and we time-align GW excess power time-frequency tilings
containing individual burst triggers to their corresponding electromagnetic
emissions. Using Monte Carlo simulations, we confirm that gains in GW energy
sensitivity of N^{1/2} are possible, where N is the number of stacked SGR
bursts. Estimated sensitivities for a mock search for gravitational waves from
the 2006 March 29 storm from SGR 1900+14 are also presented, for two GW
emission models, "fluence-weighted" and "flat" (unweighted).Comment: 17 pages, 16 figures, submitted to PR
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