11,187 research outputs found
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
Symmetry-preserving Loop Regularization and Renormalization of QFTs
A new symmetry-preserving loop regularization method proposed in \cite{ylw}
is further investigated. It is found that its prescription can be understood by
introducing a regulating distribution function to the proper-time formalism of
irreducible loop integrals. The method simulates in many interesting features
to the momentum cutoff, Pauli-Villars and dimensional regularization. The loop
regularization method is also simple and general for the practical calculations
to higher loop graphs and can be applied to both underlying and effective
quantum field theories including gauge, chiral, supersymmetric and
gravitational ones as the new method does not modify either the lagrangian
formalism or the space-time dimension of original theory. The appearance of
characteristic energy scale and sliding energy scale offers a
systematic way for studying the renormalization-group evolution of gauge
theories in the spirit of Wilson-Kadanoff and for exploring important effects
of higher dimensional interaction terms in the infrared regime.Comment: 13 pages, Revtex, extended modified version, more references adde
Generalized - Model
By parameterizing the t-j model we present a new electron correlation model
with one free parameter for high-temperature superconductivity. This model is
of symmetry. The energy spectrums are shown to be modulated by
the free parameter in the model. The solution and symmetric structures of the
Hilbert space, as well as the Bethe ansatz approach are discussed for special
cases.Comment: 13 page, Latex, to appear in J. Phys.
Exchange rate regimes and the twin economies of Hong Kong and Singapore
Based on a small, open-economy IS-LM prototype model, this paper examines the sources of macroeconomic instabilities in Hong Kong and Singapore operating under two similar cu訂ency board arrangements (CBAs). The empirical findings suggest that in general both extemal and intemal factors contribute to the macroeconomic volatilities observed in the two economies. Interestingly, whilst in Hong Kong interest rate is the single most important factor accounting for the variation in real GDP, price level and money supply, in most cases in Singapore the volatilities of these three macro variables cannot be attributed to a significant single facto r. Interest rate in both Hong Kong and Singapore moves in tandem with that of the US in the long run. In the short run, the US interest rate has both direct and indirect impacts on the two economies. Due to the high openness, international prices also affect domestic demands and prices in Hong Kong and Singapore. In addition, macroeconomic
volatilities in Hong Kong and Singapore are also attributable to the shocks in their domestic demand, though the relative magnitude of impact differs. Finally, there is evidence of a trade-off between exchange rate and interest rate targeting for the stability of money supply in Singapore. Our findings provide a useful framework for future research on the financial and monetary transmission mechanisms in the twin economies of Hong Kong and Singapore
Searching for Dark Matter Signals in the Left-Right Symmetric Gauge Model with CP Symmetry
We investigate singlet scalar dark matter (DM) candidate in a left-right
symmetric gauge model with two Higgs bidoublets (2HBDM) in which the
stabilization of the DM particle is induced by the discrete symmetries P and
CP. According to the observed DM abundance, we predict the DM direct and
indirect detection cross sections for the DM mass range from 10 GeV to 500 GeV.
We show that the DM indirect detection cross section is not sensitive to the
light Higgs mixing and Yukawa couplings except the resonance regions. The
predicted spin-independent DM-nucleon elastic scattering cross section is found
to be significantly dependent on the above two factors. Our results show that
the future DM direct search experiments can cover the most parts of the allowed
parameter space. The PAMELA antiproton data can only exclude two very narrow
regions in the 2HBDM. It is very difficult to detect the DM direct or indirect
signals in the resonance regions due to the Breit-Wigner resonance effect.Comment: 24 pages, 8 figures. minor changes and a reference added, published
in Phys. Rev.
The scalars from the topcolor scenario and the spin correlations of the top pair production at the LHC
The topcolor scenario predicts the existences of some new scalars. In this
paper, we consider the contributions of these new particles to the observables,
which are related to the top quark pair () production at the LHC. It
is found that these new particles can generate significant corrections to the
production cross section and the spin correlations.Comment: 23 pages, 4 figures; discussions and references added; agrees with
published versio
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