23,877 research outputs found
KLT-type relations for QCD and bicolor amplitudes from color-factor symmetry
Color-factor symmetry is used to derive a KLT-type relation for tree-level
QCD amplitudes containing gluons and an arbitrary number of massive or massless
quark-antiquark pairs, generalizing the expression for Yang-Mills amplitudes
originally postulated by Bern, De Freitas, and Wong. An explicit expression is
given for all amplitudes with two or fewer quark-antiquark pairs in terms of
the (modified) momentum kernel.
We also introduce the bicolor scalar theory, the "zeroth copy" of QCD,
containing massless biadjoint scalars and massive bifundamental scalars,
generalizing the biadjoint scalar theory of Cachazo, He, and Yuan. We derive
KLT-type relations for tree-level amplitudes of biadjoint and bicolor theories
using the color-factor symmetry possessed by these theories.Comment: 24 pages, 2 figures; v2: added referenc
Physics of Nonthermal Radio Sources
On December 3 and 4, 1962, the Goddard Institute for Space Studies, an office of the National Aeronautics and Space Administration, was host to an international group of astronomers and physicists who met to discuss the physics of nonthermal radio sources. This was the third in a continuing series of interdisciplinary meetings held at the Institute on topics which have a special bearing on the main lines of inquiry in the space program. The conference was organized by G. R. Burbidge of the University of California at San Diego and by L. Woltjer, then of the University of Leiden but temporarily at the Massachusetts Institute of Technology, and now of Columbia University
Aberrant Wing Pigmentation in \u3ci\u3eLibellula Luctuosa\u3c/i\u3e Specimens From Ohio
Over the past few years we obtained three female Libellula luctuosa specimens, all collected in northeast Ohio, which exhibited unusually reduced wing pigmentation. The individuals were extremely difficult to identify as most keys rely heavily upon wing pigmentation for identification of many Libellula species. A description of this aberrant wing pigmentation and a photograph are provided
Do Firms Smooth the Seasonal in Production in a Boom? Theory and Evidence
Using disaggregated production data we show that the size of seasonal cycles changes significantly over the course of the business cycle. In particular, during periods of high economy-wide activity, some industries smooth seasonal fluctuations while others exaggerate them. We interpret this finding using a simple analytical model that describes the conditions under which seasonal and cyclical fluctuations can be separated. Our model implies that seasonal fluctuations can safely be disentangled from cyclical fluctuations only when the marginal cost of production is linear, and the variation in demand and cost satisfy certain (restrictive) conditions. The model also suggests that inventory movements can be used to isolate the role of demand shifts in generating any interaction between seasonal cycles and business cycles. Thus, the empirical analysis involves studying the variation in seasonally unadjusted patterns of production and inventory accumulation over different phases of the business cycle. Our finding that seasonals shrink during booms and that firms carry more inventories into high sales seasons during a boom leads us to conclude that for several industries, marginal cost slopes up at an increasing rate. Conversely, in a couple of industries we find that seasonal swings in production are exaggerated during booms and that inventories are drawn down prior to high sales seasons, suggesting that marginal costs curves flatten as production increases. Overall, we find considerable evidence that there are non-linear interactions between business cycles and seasonal cycles.
Trapping and Characterization of the Reaction Intermediate in Cyclodextrin Glycosyltransferase by Use of Activated Substrates and a Mutant Enzyme
Cyclodextrin glycosyltransferases (CGTases) catalyze the degradation of starch into linear or cyclic oligosaccharides via a glycosyl transfer reaction occurring with retention of anomeric configuration. They are also shown to catalyze the coupling of maltooligosaccharyl fluorides. Reaction is thought to proceed via a double-displacement mechanism involving a covalent glycosyl-enzyme intermediate. This intermediate can be trapped by use of 4-deoxymaltotriosyl α-fluoride (4DG3αF). This substrate contains a good leaving group, fluoride, thus facilitating formation of the intermediate, but cannot undergo the transglycosylation step since the nucleophilic hydroxyl group at the 4-position is missing. When 4DG3αF was reacted with wild-type CGTase (Bacillus circulans 251), it was found to be a slow substrate (kcat = 2 s-1) compared with the parent glycosyl fluoride, maltotriosyl R-fluoride (kcat = 275 s-1). Unfortunately, a competing hydrolysis reaction reduces the lifetime of the intermediate precluding its trapping and identification. However, when 4DG3αF was used in the presence of the presumed acid/base catalyst mutant Glu257Gln, the intermediate could be trapped and analyzed because the first step remained fast while the second step was further slowed (kcat = 0.6 s-1). Two glycosylated peptides were identified in a proteolytic digest of the inhibited enzyme by means of neutral loss tandem mass spectrometry. Edman sequencing of these labeled peptides allowed identification of Asp229 as the catalytic nucleophile and provided evidence for a covalent intermediate in CGTase. Asp229 is found to be conserved in all members of the family 13 glycosyl transferases.
Exploring compressed supersymmetry with same-sign top quarks at the Large Hadron Collider
In compressed supersymmetry, a light top squark naturally mediates efficient
neutralino pair annihilation to govern the thermal relic abundance of dark
matter. I study the LHC signal of same-sign leptonic top-quark decays from
gluino and squark production, which follows from gluino decays to top plus stop
followed by the stop decaying to a charm quark and the LSP in these models.
Measurements of the numbers of jets with heavy-flavor tags in the same-sign
lepton events can be used to confirm the origin of the signal. Summed
transverse momentum observables provide an estimate of an effective
superpartner mass, which is correlated with the gluino mass. Measurements of
invariant mass endpoints from the visible products of gluino decays do not
allow direct determination of superpartner masses, but can place constraints on
them, including lower bounds on the gluino mass as a function of the top-squark
mass.Comment: 22 pages. v2: Discussion of competition between 2-body and 4-body
stop decays corrected. References adde
Reciprocal relativity of noninertial frames: quantum mechanics
Noninertial transformations on time-position-momentum-energy space {t,q,p,e}
with invariant Born-Green metric ds^2=-dt^2+dq^2/c^2+(1/b^2)(dp^2-de^2/c^2) and
the symplectic metric -de/\dt+dp/\dq are studied. This U(1,3) group of
transformations contains the Lorentz group as the inertial special case. In the
limit of small forces and velocities, it reduces to the expected Hamilton
transformations leaving invariant the symplectic metric and the nonrelativistic
line element ds^2=dt^2. The U(1,3) transformations bound relative velocities by
c and relative forces by b. Spacetime is no longer an invariant subspace but is
relative to noninertial observer frames. Born was lead to the metric by a
concept of reciprocity between position and momentum degrees of freedom and for
this reason we call this reciprocal relativity.
For large b, such effects will almost certainly only manifest in a quantum
regime. Wigner showed that special relativistic quantum mechanics follows from
the projective representations of the inhomogeneous Lorentz group. Projective
representations of a Lie group are equivalent to the unitary reprentations of
its central extension. The same method of projective representations of the
inhomogeneous U(1,3) group is used to define the quantum theory in the
noninertial case. The central extension of the inhomogeneous U(1,3) group is
the cover of the quaplectic group Q(1,3)=U(1,3)*s H(4). H(4) is the
Weyl-Heisenberg group. A set of second order wave equations results from the
representations of the Casimir operators
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