54,152 research outputs found
Symmetry of Solutions for a Fractional System
We consider the following equations: \begin{equation*}
\left\{\begin{array}{ll} (-\triangle)^{\alpha/2}u(x)=f(v(x)), \\
(-\triangle)^{\beta/2}v(x)=g(u(x)), &x \in R^{n},\\ u,v\geq 0, &x \in R^{n},
\end{array} \right. \end{equation*} for continuous and . Under some natural assumptions on and , by applying the
\emph{method of moving planes} directly to the system, we obtain symmetry on
non-negative solutions without any decay assumption on the solutions at
infinity
Co-evolution of Extreme Star Formation and Quasar: hints from {\it Herschel} and the Sloan Digital Sky Survey
Using the public data from the Herschel wide field surveys, we study the
far-infrared properties of optical-selected quasars from the Sloan Digital Sky
Survey. Within the common area of , we have identified the
far-infrared counterparts for 354 quasars, among which 134 are highly secure
detections in the Herschel band (signal-to-noise ratios ).
This sample is the largest far-infrared quasar sample of its kind, and spans a
wide redshift range of . Their far-infrared spectral
energy distributions, which are due to the cold dust components within the host
galaxies, are consistent with being heated by active star formation. In most
cases (\%), their total infrared luminosities as inferred from only
their far-infrared emissions () already exceed
, and thus these objects qualify as ultra-luminous infrared
galaxies. There is no correlation between and the absolute
magnitudes, the black hole masses or the X-ray luminosities of the quasars,
which further support that their far-infrared emissions are not due to their
active galactic nuclei. A large fraction of these objects
() have star formation rates . Such extreme starbursts among optical quasars, however,
is only a few per cent. This fraction varies with redshift, and peaks at around
. Among the entire sample, 136 objects have secure estimates of
their cold-dust temperatures (), and we find that there is a dramatic
increasing trend of with increasing . We interpret this
trend as the envelope of the general distribution of infrared galaxies on the
(, ) plane.Comment: 26 pages, 20 figures, Accepted for publication in Ap
On the Limited Sizes of Dusty Starbursting Regions at High Redshifts
Using the far-infrared data obtained by the Herschel Space Observatory, we
study the relation between the infrared luminosity (L_IR) and the dust
temperature (T) of dusty starbursting galaxies at high redshifts (high-z). We
focus on the total infrared luminosity from the cold-dust component
(L_IR^(cd)), whose emission can be described by a modified black body (MBB) of
a single temperature (T_mbb). An object on the (L_IR^(cd), T_mbb) plane can be
explained by the equivalent of the Stefan-Boltzmann law for a MBB with an
effective radius of R_eff. We show that R_eff is a good measure of the combined
size of the dusty starbursting regions (DSBRs) of the host galaxy. In at least
one case where the individual DSBRs are well resolved through strong
gravitational lensing, R_eff is consistent with the direct size measurement. We
show that the observed L_IR-T relation is simply due to the limited R_eff (<~ 2
kpc). The small R_eff values also agree with the compact sizes of the DSBRs
seen in the local universe. However, previous interferometric observations to
resolve high-z dusty starbursting galaxies often quote much larger sizes. This
inconsistency can be reconciled by the blending effect when considering that
the current interferometry might still not be of sufficient resolution. From
R_eff we infer the lower limits to the volume densities of the star formation
rate ("minSFR3D") in the DSBRs, and find that the - relation
outlines a boundary on the (L_IR^(cd), T) plane, below which is the "zone of
avoidance" in terms of minSFR3D.Comment: Submitted to ApJ
Determine Arbitrary Feynman Integrals by Vacuum Integrals
By introducing an auxiliary parameter, we find a new representation for
Feynman integrals, which defines a Feynman integral by analytical continuation
of a series containing only vacuum integrals. The new representation therefore
conceptually translates the problem of computing Feynman integrals to the
problem of performing analytical continuations. As an application of the new
representation, we use it to construct a novel reduction method for multi-loop
Feynman integrals, which is expected to be more efficient than known
integration-by-parts reduction method. Using the new method, we successfully
reduced all complicated two-loop integrals in process and process.Comment: Version published in PRD (Rapid Communication
Comprehensive description of production in proton-proton collisions at collider energies
We employ a small Color Glass Condensate (CGC)+ Non-Relativistic QCD
(NRQCD) formalism to compute production at low in
proton-proton collisions at collider energies. Very good agreement is obtained
for total cross-sections, rapidity distributions and low momentum
distributions. Similar agreement is obtained for production. We
observe an overlap region in where our results match smoothly to
those obtained in a next-to-leading order (NLO) collinearly factorized NRQCD
formalism. The relative contribution of color singlet and color octet
contributions can be quantified in the CGC+NRQCD framework, with the former
contributing approximately of the total cross-section.Comment: 6 pages, 3 figures, typos corrected, final version accepted by
Physical Review Letter
New factorization theory for heavy quarkonium production and decay
The widely used nonrelativistic QCD (NRQCD) factorization theory now
encounters some notable difficulties in describing quarkonium production. This
may be due to the inadequate treatment of soft hadrons emitted in the
hadronization process, which causes bad convergence of velocity expansion in
NRQCD. In this paper, starting from QCD we propose a rigorously defined
factorization approach, soft gluon factorization (SGF), to better deal with the
effects of soft hadrons. After a careful velocity expansion, the SGF can be as
simple as the NRQCD factorization in phenomenological studies, but has a much
better convergence. The SGF may provide a new insight to understand the
mechanisms of quarkonium production and decay.Comment: 12 pages, 3 figures, version published in PR
Symmetry and nonexistence of positive solutions for fractional systems
This paper is devoted to study the nonexistence results of positive solutions
for the following fractional Hnon system \begin{eqnarray*}\left\{
\begin{array}{lll}
&(-\triangle)^{\alpha/2}u=|x|^av^p,~~~&x\in R^n,
&(-\triangle)^{\alpha/2}v=|x|^bu^q,~~~ &x\in R^n,
&u\geq0, v\geq 0,
\end{array}
\right. \end{eqnarray*} where , , , ,
. Using a direct method of moving planes, we prove non-existence of
positive solution in the subcritical case
Extracting Parton Distribution Functions from Lattice QCD Calculations
Parton distribution functions (PDFs) are nonperturbative quantities
describing the relation between a hadron and quarks and gluons within it. We
propose to extract PDFs from QCD global analysis of "data" generated by lattice
QCD calculations of good "lattice cross sections", which are basically
single-hadron matrix elements that are lattice QCD calculable and perturbative
QCD factorizable into the PDFs. To demonstrate the existence of good "lattice
cross sections", we take quasi-quark distribution introduced by Ji [1] as a
case study to show that it could be factorized into the PDFs to all orders in
perturbation theory if it can be multiplicatively renormalized. We calculate
the factorized coefficients at the next-to-leading order in .Comment: references updated, version published at PR
Hom-Nijienhuis operator and *-extension of Hom-Lie Superalgebras
In this paper, we study hom-Lie superalgebras. We give the definition of
hom-Nijienhuis operators of regualr hom-Lie superalgebras and show that the
deformation generated by a hom-Nijienhuis operator is trivial. Moreover, we
introduce the definition of -extensions of Hom-Lie superalgebras and show
that -extensions preserve many properties such as nilpotency, solvability
and decomposition in some sense. We also investigate the equivalence of
-extensions.Comment: arXiv admin note: text overlap with arXiv:1005.0140 by other author
Theory for quarkonium: from NRQCD factorization to soft gluon factorization
We demonstrate that the recently proposed soft gluon factorization (SGF) is
equivalent to the nonrelativistic QCD (NRQCD) factorization for heavy
quarkonium production or decay, which means that for any given process these
two factorization theories are either both valid or both violated. We use two
methods to achieve this conclusion. In the first method, we apply the two
factorization theories to the physical process . Our
explicit calculation shows that both SGF and NRQCD can correctly reproduce low
energy physics of full QCD, and thus the two factorizations are equivalent. In
the second method, by using equations of motion we successfully deduce SGF from
NRQCD effective field theory. By identifying SGF with NRQCD factorization, we
establish relations between the two factorization theories and prove the
generalized Gremm-Kapustin relations as a by product. Comparing with the NRQCD
factorization, the advantage of SGF is that it resums the series of
relativistic corrections originated from kinematic effects to all powers, which
gives rise to a better convergence in relativistic expansion.Comment: 15 pages, 1 figur
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