21,214 research outputs found
A More Precise Extraction of |V_{cb}| in HQEFT of QCD
The more precise extraction for the CKM matrix element |V_{cb}| in the heavy
quark effective field theory (HQEFT) of QCD is studied from both exclusive and
inclusive semileptonic B decays. The values of relevant nonperturbative
parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD.
Using the most recent experimental data for B decay rates, |V_{cb}| is updated
to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l
\nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l
\nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from
inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure
Geometric engineering of (framed) BPS states
BPS quivers for N=2 SU(N) gauge theories are derived via geometric
engineering from derived categories of toric Calabi-Yau threefolds. While the
outcome is in agreement of previous low energy constructions, the geometric
approach leads to several new results. An absence of walls conjecture is
formulated for all values of N, relating the field theory BPS spectrum to large
radius D-brane bound states. Supporting evidence is presented as explicit
computations of BPS degeneracies in some examples. These computations also
prove the existence of BPS states of arbitrarily high spin and infinitely many
marginal stability walls at weak coupling. Moreover, framed quiver models for
framed BPS states are naturally derived from this formalism, as well as a
mathematical formulation of framed and unframed BPS degeneracies in terms of
motivic and cohomological Donaldson-Thomas invariants. We verify the
conjectured absence of BPS states with "exotic" SU(2)_R quantum numbers using
motivic DT invariants. This application is based in particular on a complete
recursive algorithm which determine the unframed BPS spectrum at any point on
the Coulomb branch in terms of noncommutative Donaldson-Thomas invariants for
framed quiver representations.Comment: 114 pages; v2:minor correction
Lifetime Difference and Endpoint effect in the Inclusive Bottom Hadron Decays
The lifetime differences of bottom hadrons are known to be properly explained
within the framework of heavy quark effective field theory(HQEFT) of QCD via
the inverse expansion of the dressed heavy quark mass. In general, the spectrum
around the endpoint region is not well behaved due to the invalidity of
expansion near the endpoint. The curve fitting method is adopted to treat the
endpoint behavior. It turns out that the endpoint effects are truly small and
the explanation on the lifetime differences in the HQEFT of QCD is then well
justified. The inclusion of the endpoint effects makes the prediction on the
lifetime differences and the extraction on the CKM matrix element
more reliable.Comment: 11 pages, Revtex, 10 figures, 6 tables, published versio
Spin Polarisability of the Nucleon in the Heavy Baryon Effective Field Theory
We have constructed a heavy baryon effective field theory with photon as an
external field in accordance with the symmetry requirements similar to the
heavy quark effective field theory. By treating the heavy baryon and
anti-baryon equally on the same footing in the effective field theory, we have
calculated the spin polarisabilities of the nucleon at
third order and at fourth-order of the spin-dependent Compton scattering. At
leading order (LO), our results agree with the corresponding results of the
heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the
results show a large correction to the ones in the heavy baryon chiral
perturbation theory due to baryon-antibaryon coupling terms. The low energy
theorem is satisfied both at LO and at NLO. The contributions arising from the
heavy baryon-antibaryon vertex were found to be significant and the results of
the polarisabilities obtained from our theory is much closer to the
experimental data.Comment: 21pages, title changed, minimal correction
Large Component QCD and Theoretical Framework of Heavy Quark Effective Field Theory
Based on a large component QCD derived directly from full QCD by integrating
over the small components of quark fields with , an
alternative quantization procedure is adopted to establish a basic theoretical
framework of heavy quark effective field theory (HQEFT) in the sense of
effective quantum field theory. The procedure concerns quantum generators of
Poincare group, Hilbert and Fock space, anticommutations and velocity
super-selection rule, propagator and Feynman rules, finite mass corrections,
trivialization of gluon couplings and renormalization of Wilson loop. The
Lorentz invariance and discrete symmetries in HQEFT are explicitly illustrated.
Some new symmetries in the infinite mass limit are discussed. Weak transition
matrix elements and masses of hadrons in HQEFT are well defined to display a
manifest spin-flavor symmetry and corrections. A simple trace
formulation approach is explicitly demonstrated by using LSZ reduction formula
in HQEFT, and shown to be very useful for parameterizing the transition form
factors via expansion. As the heavy quark and antiquark fields in HQEFT
are treated on the same footing in a fully symmetric way, the quark-antiquark
coupling terms naturally appear and play important roles for simplifying the
structure of transition matrix elements, and for understanding the concept of
`dressed heavy quark' - hadron duality. In the case that the `longitudinal' and
`transverse' residual momenta of heavy quark are at the same order of power
counting, HQEFT provides a consistent approach for systematically analyzing
heavy quark expansion in terms of . Some interesting features in
applications of HQEFT to heavy hadron systems are briefly outlined.Comment: 59 pages, RevTex, no figures, published versio
Ultrafast, laser-scanning time-stretch microscopy with visible light
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