9,404 research outputs found
Two-Loop integrals for CP-even heavy quarkonium production and decays: Elliptic Sectors
By employing the differential equations, we compute analytically the elliptic
sectors of two-loop master integrals appearing in the NNLO QCD corrections to
CP-even heavy quarkonium exclusive production and decays, which turns out to be
the last and toughest part in the relevant calculation. The integrals are found
can be expressed as Goncharov polylogarithms and iterative integrals over
elliptic functions. The master integrals may be applied to some other NNLO QCD
calculations about heavy quarkonium exclusive production, like
, ,~and~, heavy quarkonium exclusive
decays, and also the CP-even heavy quarkonium inclusive production and decays.Comment: 23 pages, 3 figures, more discussions and references adde
Heating and cooling of coronal loops observed by SDO
Context: One of the most prominent processes suggested to heat the corona to
well above 10^6 K builds on nanoflares, short bursts of energy dissipation.
Aims: We compare observations to model predictions to test the validity of
the nanoflare process.
Methods: Using extreme UV data from AIA/SDO and HMI/SDO line-of-sight
magnetograms we study the spatial and temporal evolution of a set of loops in
active region AR 11850.
Results: We find a transient brightening of loops in emission from Fe xviii
forming at about 7.2 MK while at the same time these loops dim in emission from
lower temperatures. This points to a fast heating of the loop that goes along
with evaporation of material that we observe as apparent upward motions in the
image sequence. After this initial phases lasting for some 10 min, the loops
brighten in a sequence of AIA channels showing cooler and cooler plasma,
indicating the cooling of the loops over a time scale of about one hour. A
comparison to the predictions from a 1D loop model shows that this observation
supports the nanoflare process in (almost) all aspects. In addition, our
observations show that the loops get broader while getting brighter, which
cannot be understood in a 1D model.Comment: 9 pages, 7 figures, accepted by A&
Annihilation Rates of Heavy S-wave Quarkonia in Salpeter Method
The annihilation rates of vector charmonium and bottomonium
states and , and are estimated in the relativistic Salpeter method.
We obtained keV,
keV,
keV,
keV,
keV,
keV and
keV. In our
calculations, special attention is paid to the relativistic correction, which
is important and can not be ignored for excited , and higher excited
states.Comment: 10 pages,2 figures, 5 table
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