12,049 research outputs found
QCD Compositeness as Revealed in Exclusive Vector Boson Reactions through Double-Photon Annihilation: and
We study the exclusive double-photon annihilation processes, and where the is a neutral vector meson produced in the
forward kinematical region: and . We
show how the differential cross sections , as predicted by
QCD, have additional falloff in the momentum transfer squared due to the
QCD compositeness of the hadrons, consistent with the leading-twist
fixed- scaling laws. However, even though they are exclusive
channels and not associated with the conventional electron-positron
annihilation process these total cross
sections and integrated over the dominant forward- and backward-
angular domains, scale as , and thus contribute to the leading-twist
scaling behavior of the ratio . We generalize these results to
exclusive double-electroweak vector-boson annihilation processes accompanied by
the forward production of hadrons, such as and . These results can also be applied to the exclusive production
of exotic hadrons such as tetraquarks, where the cross-section scaling behavior
can reveal their multiquark nature.Comment: 10 page
QCD Constituent Counting Rules for Neutral Vector Mesons
QCD constituent counting rules define the scaling behavior of exclusive
hadronic scattering and electromagnetic scattering amplitudes at high momentum
transfer in terms of the total number of fundamental constituents in the
initial and final states participating in the hard subprocess. The scaling laws
reflect the twist of the leading Fock state for each hadron and hence the
leading operator that creates the composite state from the vacuum. Thus, the
constituent counting scaling laws can be used to identify the twist of exotic
hadronic candidates such as tetraquarks and pentaquarks. Effective field
theories must consistently implement the scaling rules in order to be
consistent with the fundamental theory. Here we examine how one can apply
constituent counting rules for the exclusive production of one or two neutral
vector mesons in annihilation, processes in which the can
couple via intermediate photons. In case of a (narrow) real , the photon
virtuality is fixed to a precise value , in effect treating
the as a single fundamental particle. Each real thus contributes to
the constituent counting rules with . In effect, the leading
operator underlying the has twist 1. Thus, in the specific physical case
of single or double on-shell production via intermediate photons, the
predicted scaling from counting rules coincides with Vector Meson Dominance
(VMD), an effective theory that treats as an elementary field. However,
the VMD prediction fails in the general case where the is not coupled
through an elementary photon field, and then the leading-twist interpolating
operator has twist . Analogous effects appear in scattering
processes.Comment: 15 page
Phase Structure of the Interacting Vector Boson Model
The two-fluid Interacting Vector Boson Model (IVBM) with the U(6) as a
dynamical group possesses a rich algebraic structure of physical interesting
subgroups that define its distinct exactly solvable dynamical limits. The
classical images corresponding to different dynamical symmetries are obtained
by means of the coherent state method. The phase structure of the IVBM is
investigated and the following basic phase shapes, connected to a specific
geometric configurations of the ground state, are determined: spherical,
, unstable, O(6), and axially deformed
shape, . The ground state quantum phase transitions
between different phase shapes, corresponding to the different dynamical
symmetries and mixed symmetry case, are investigated.Comment: 9 pages, 10 figure
Arbitrage-Free Bond Pricing with Dynamic Macroeconomic Models
We examine the relationship between monetary-policy-induced changes in short interest rates and yields on long-maturity default-free bonds. The volatility of the long end of the term structure and its relationship with monetary policy are puzzling from the perspective of simple structural macroeconomic models. We explore whether richer models of risk premiums, specifically stochastic volatility models combined with Epstein-Zin recursive utility, can account for such patterns. We study the properties of the yield curve when inflation is an exogenous process and compare this to the yield curve when inflation is endogenous and determined through an interest-rate/Taylor rule. When inflation is exogenous, it is difficult to match the shape of the historical average yield curve. Capturing its upward slope is especially difficult as the nominal pricing kernel with exogenous inflation does not exhibit any negative autocorrelation - a necessary condition for an upward sloping yield curve as shown in Backus and Zin (1994). Endogenizing inflation provides a substantially better fit of the historical yield curve as the Taylor rule provides additional flexibility in introducing negative autocorrelation into the nominal pricing kernel. Additionally, endogenous inflation provides for a flatter term structure of yield volatilities which better fits historical bond data.
Comparing and characterizing some constructions of canonical bases from Coxeter systems
The Iwahori-Hecke algebra of a Coxeter system has a
"standard basis" indexed by the elements of and a "bar involution" given by
a certain antilinear map. Together, these form an example of what Webster calls
a pre-canonical structure, relative to which the well-known Kazhdan-Lusztig
basis of is a canonical basis. Lusztig and Vogan have defined a
representation of a modified Iwahori-Hecke algebra on the free
-module generated by the set of twisted involutions in
, and shown that this module has a unique pre-canonical structure satisfying
a certain compatibility condition, which admits its own canonical basis which
can be viewed as a generalization of the Kazhdan-Lusztig basis. One can modify
the parameters defining Lusztig and Vogan's module to obtain other
pre-canonical structures, each of which admits a unique canonical basis indexed
by twisted involutions. We classify all of the pre-canonical structures which
arise in this fashion, and explain the relationships between their resulting
canonical bases. While some of these canonical bases are related in a trivial
fashion to Lusztig and Vogan's construction, others appear to have no simple
relation to what has been previously studied. Along the way, we also clarify
the differences between Webster's notion of a canonical basis and the related
concepts of an IC basis and a -kernel.Comment: 32 pages; v2: additional discussion of relationship between canonical
bases, IC bases, and P-kernels; v3: minor revisions; v4: a few corrections
and updated references, final versio
Arbitrage-free bond pricing with dynamic macroeconomic models
The authors examine the relationship between changes in short-term interest rates induced by monetary policy and the yields on long-maturity default-free bonds. The volatility of the long end of the term structure and its relationship with monetary policy are puzzling from the perspective of simple structural macroeconomic models. The authors explore whether richer models of risk premiums, specifically stochastic volatility models combined with Epstein-Zin recursive utility, can account for such patterns. They study the properties of the yield curve when inflation is an exogenous process and compare this with the yield curve when inflation is endogenous and determined through an interest rate (Taylor) rule. When inflation is exogenous, it is difficult to match the shape of the historical average yield curve. Capturing its upward slope is especially difficult because the nominal pricing kernel with exogenous inflation does not exhibit any negative autocorrelation-a necessary condition for an upward-sloping yield curve, as shown in Backus and Zin. Endogenizing inflation provides a substantially better fit of the historical yield curve because the Taylor rule provides additional flexibility in introducing negative autocorrelation into the nominal pricing kernel. Additionally, endogenous inflation provides for a flatter term structure of yield volatilities, which better fits historical bond data.Bonds - Prices ; Macroeconomics
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