9,614 research outputs found
Decays of and into vector and pseudoscalar meson and the pseudoscalar glueball- mixing
We introduce a parametrization scheme for where
the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation
(DOZI) can be parametrized by certain parameters with explicit physical
interpretations. This scheme can be used to clarify the glueball-
mixing within the pseudoscalar mesons. We also include the contributions from
the electromagnetic (EM) decays of and via
. Via study of the isospin violated
channels, such as , ,
and , reasonable constraints on the EM decay
contributions are obtained. With the up-to-date experimental data for
, and , etc, we arrive at a consistent description of the mentioned
processes with a minimal set of parameters. As a consequence, we find that
there exists an overall suppression of the form factors,
which sheds some light on the long-standing " puzzle". By determining
the glueball components inside the pseudoscalar and in
three different glueball- mixing schemes, we deduce that the lowest
pseudoscalar glueball, if exists, has rather small component, and it
makes the a preferable candidate for glueball.Comment: Revised version to appear on J. Phys. G; An error in the code was
corrected. There's slight change to the numerical results, while the
conclusion is intac
Antenna subtraction for jet production observables in full colour at NNLO
We describe the details of the calculation of the full colour NNLO QCD corrections to jet production observables at the LHC with antenna subtraction. All relevant matrix elements for the process pp → jj at NNLO in full colour are colour-decomposed and given in a N and n expansion, making identification of leading and subleading colour contributions transparent. The colour-ordered antenna subtraction method has previously successfully been used to construct the NNLO subtraction terms for processes with up to five partons or in the leading colour approximation. However, it is challenged by the more involved subleading colour structure of the squared matrix elements in processes with six or more partons. Here, we describe the methods needed to successfully construct the NNLO subtraction terms for the subleading colour contributions to dijet production within the antenna subtraction formalism
NNLO QCD corrections in full colour for jet production observables at the LHC
Calculations for processes involving a high multiplicity of coloured particles often employ a leading colour approximation, where only the leading terms in the expansion of the number of colours Nc and the number of flavours nf are retained. This approximation of the full colour result is motivated by the 1/N2 c suppression of the first subleading terms and by the increasing complexity of including subleading colour contributions to the calculation. In this work, we present the calculations using the antenna subtraction method in the NNLOjet framework for the NNLO QCD corrections at full colour for several jet observables at the LHC. The single jet inclusive cross section is calculated doubly differential in transverse momentum and absolute rapidity and compared with the CMS measurement at 13 TeV. A calculation for dijet production doubly differential in dijet mass and rapidity difference is also performed and compared with the ATLAS 7 TeV data. Lastly, a triply differential dijet cross section in average transverse momentum, rapidity separation and dijet system boost is calculated and compared with the CMS 8 TeV data. The impact of the subleading colour contributions to the leading colour approximation is assessed in detail for all three types of observables and as a function of the jet cone size. The subleading colour contributions play a potentially sizable role in the description of the triply differential distributions, which probe kinematical configurations that are not easily accessed by any of the other observables
Antenna subtraction for jet production observables in full colour at NNLO
We describe the details of the calculation of the full colour NNLO QCD corrections to jet production observables at the LHC with antenna subtraction. All relevant matrix elements for the process pp → jj at NNLO in full colour are colour-decomposed and given in a N and n expansion, making identification of leading and subleading colour contributions transparent. The colour-ordered antenna subtraction method has previously successfully been used to construct the NNLO subtraction terms for processes with up to five partons or in the leading colour approximation. However, it is challenged by the more involved subleading colour structure of the squared matrix elements in processes with six or more partons. Here, we describe the methods needed to successfully construct the NNLO subtraction terms for the subleading colour contributions to dijet production within the antenna subtraction formalism
NNLO QCD corrections in full colour for jet production observables at the LHC
Calculations for processes involving a high multiplicity of coloured particles often employ a leading colour approximation, where only the leading terms in the expansion of the number of colours N and the number of flavours n are retained. This approximation of the full colour result is motivated by the 1/N suppression of the first subleading terms and by the increasing complexity of including subleading colour contributions to the calculation. In this work, we present the calculations using the antenna subtraction method in the NNLOJET framework for the NNLO QCD corrections at full colour for several jet observables at the LHC. The single jet inclusive cross section is calculated doubly differential in transverse momentum and absolute rapidity and compared with the CMS measurement at 13 TeV. A calculation for dijet production doubly differential in dijet mass and rapidity difference is also performed and compared with the ATLAS 7 TeV data. Lastly, a triply differential dijet cross section in average transverse momentum, rapidity separation and dijet system boost is calculated and compared with the CMS 8 TeV data. The impact of the subleading colour contributions to the leading colour approximation is assessed in detail for all three types of observables and as a function of the jet cone size. The subleading colour contributions play a potentially sizable role in the description of the triply differential distributions, which probe kinematical configurations that are not easily accessed by any of the other observables
The Impact of Small-Scale Structure on Cosmological Ionization Fronts and Reionization
The propagation of cosmological ionization fronts during the reionization of
the universe is strongly influenced by small-scale gas inhomogeneities due to
structure formation. These inhomogeneities include both collapsed minihalos,
which are generally self-shielding, and lower-density structures, which are
not. The minihalos are dense and sufficiently optically-thick to trap
intergalactic ionization fronts, blocking their path and robbing them of
ionizing photons until the minihalo gas is expelled as an evaporative wind. The
lower-density structures do not trap these fronts, but they can slow them down
by increasing the overall recombination rate in the intergalactic medium. In
this paper we study the effects of both types of inhomogeneities, including
nonlinear clustering effects, and we find that both IGM clumping and collapsed
minihalos have significant yet qualitatively different impacts on reionization.
While the number density of minihalos on average increases strongly with time,
the density of minihalos inside H II regions around ionizing sources is largely
constant. Thus the impact of minihalos is essentially to decrease the number of
ionizing photons available to the IGM at all epochs, which is equivalent to a
reduction in the luminosity of each source. On the other hand, the effect of
IGM clumping increases strongly with time, slowing down reionization and
extending it. Thus while the impact of minihalos is largely degenerate with the
unknown source efficiency, IGM clumping can help significantly in reconciling
the recent observations of cosmic microwave background polarization with quasar
absorption spectra at z~6, which together point to an early but extended
reionization epoch.Comment: 15 pages, 9 figures, minor revisions to respond to referee comments,
accepted for publication in The Astrophysical Journa
- …