265 research outputs found
An open toss problem
We discuss some particular cases of the following problem. Each of m persons tosses
a coin. Those who get heads stay for the next round. Those who get tails are eliminated; however,
if all persons get tails in a round, they move to the next round (as if each of them had got a head).
The problem is to find the possibility that exactly one person is left after r rounds. All coins are
considered identical but not necessarily fair
Renormalization of the baryon axial vector current in large-N_c chiral perturbation theory
The baryon axial vector current is computed at one-loop order in heavy baryon
chiral perturbation theory in the large-N_c limit, where N_c is the number of
colors. Loop graphs with octet and decuplet intermediate states cancel to
various orders in N_c as a consequence of the large-N_c spin-flavor symmetry of
QCD baryons. These cancellations are explicitly shown for the general case of
N_f flavors of light quarks. In particular, a new generic cancellation is
identified in the renormalization of the baryon axial vector current at
one-loop order. A comparison with conventional heavy baryon chiral perturbation
theory is performed at the physical values N_c=3, N_f=3.Comment: REVTex4, 29 pages, 2 figures, 6 tables. Equations (32) and (81)
corrected. Some typos fixed. Results and conclusions remain unchange
On the structure of large N cancellations in baryon chiral perturbation theory
We show how to compute loop graphs in heavy baryon chiral perturbation theory
including the full functional dependence on the ratio of the Delta--nucleon
mass difference to the pion mass, while at the same time automatically
incorporating the 1/N cancellations that follow from the large-N spin-flavor
symmetry of baryons in QCD. The one-loop renormalization of the baryon axial
vector current is studied to demonstrate the procedure. A new cancellation is
identified in the one-loop contribution to the baryon axial vector current. We
show that loop corrections to the axial vector currents are exceptionally
sensitive to deviations of the ratios of baryon-pion axial couplings from SU(6)
values
Determination of the Kobayashi-Maskawa-Cabibbo matrix element V_{us} under various flavor-symmetry-breaking models in hyperon semileptonic decays
We study the success to describe hyperon semileptonic decays of four models
that incorporate second-order SU(3) symmetry breaking corrections. The criteria
to assess their success is by determining V_{us} in each of the three relevant
hyperon semileptonic decays and comparing the values obtained with one another
and also with the one that comes from K_{l3} decays. A strong dependence on the
particular symmetry breaking model is observed. Values of V_{us} which do not
agree with the one of K_{l3} are generally obtained. However, in the context of
chiral perturbation theory, only the model whose corrections are O(m_s) and
O(m_s^{3/2}) is successful. Using its predictions for the f_1 form factors one
can quote a value of V_{us} from this model, namely, V_{us}=0.2176\pm 0.0026,
which is in excellent agreement with the K_{l3} one.Comment: Final versio
Large N_c, Constituent Quarks, and N, Delta Charge Radii
We show how one may define baryon constituent quarks in a rigorous manner,
given physical assumptions that hold in the large-N_c limit of QCD. This
constituent picture gives rise to an operator expansion that has been used to
study large-N_c baryon observables; here we apply it to the case of charge
radii of the N and Delta states, using minimal dynamical assumptions. For
example, one finds the relation r_p^2 - r_{Delta^+}^2 = r_n^2 - r_{Delta^0}^2
to be broken only by three-body, O(1/N_c^2) effects for any N_c.Comment: 15 pages, 1 eps figure. Version to appear in Phys. Rev.
Iron therapy substantially restores qEEG maturational lag among iron-deficient anemic infants
Objective: To use quantitative electroencephalography (qEEG) to assess the impact of iron-deficiency anemia on central nervous system maturation in the first year of life. Method: Twenty-five infants (3–12 months old) presenting ferropenic anemia (IDA) and 25 healthy controls (CTL1), matched by age/gender with the former, were studied in two stages. Electroencephalogram during spontaneous sleep was recorded from all participants; the fast Fourier transform was calculated to obtain absolute power (AP) and relative power (RP) qEEG measures. In the first stage, a qEEG comparison between CTL1 and IDA was performed. Second stage consisted in comparing qEEG of the IDA infants before and after supplementation with iron (IDA-IS group), and comparing qEEG of the IDA-IS group with another control age-matched group (CTL2). Non-parametric multivariate permutation tests (NPT) were applied to assess differences between CTL1 and IDA groups, as well as IDA vs. IDA-IS, and IDA-IS vs. CTL2. Results: More power in slow frequency bands and less power in fast frequency bands in 64% of IDA babies were observed. NPT evinced higher alpha AP and RP (P < 0.001), less theta AP, and less delta and theta RP in CTL1 than in IDA. After iron-restoration therapy, alpha AP and RP increased while theta AP and theta and delta RP decreased, reaching almost normal values. Discussion: This work reveals CNS developmental delay through the study of qEEG (less rapid and more slow frequencies) which recovered significantly with iron supplementation. It is concluded that IDA constitutes a high risk factor for a lag of CNS maturation.CONACYT-Project No. CO1/40257-A1
Soliton Models for the Nucleon and Predictions for the Nucleon Spin Structure
In these lectures the three flavor soliton approach for baryons is reviewed.
Effects of flavor symmetry breaking in the baryon wave--functions on axial
current matrix elements are discussed. A bosonized chiral quark model is
considered to outline the computation of spin dependent nucleon structure
functions in the soliton picture.Comment: 12 pages, Lectures presented at the Advanced Study Institute Symmetry
and Spin, Prague, 2001, to appear in the proceedings. References correcte
Financialisation at a Watershed in the USA
In the period following the Great Recession of 2007-9 the financialisation of the US economy reached a watershed characterised by stagnant financial profits, falling proportions of financial sector and mortgage debt, and rising proportion of public debt. The main macroeconomic indicators of financialisation in the USA show structural breaks that can be dated around the period of the Great Recession. The reliance of households on the formal financial system appears to have weakened for the first time since the early 1980s. The financial sector has lacked the dynamism of the previous three decades becoming more reliant on government. The state has increased its own indebtedness and supported large financial institutions via unconventional monetary policy measures. At the same time, state intervention has tightened the regulatory framework for big banks. The future path of financialisation in the USA will depend heavily on government policy with regard to state debt and financial regulation, although the scope for boosting financialisation is narrow
Contributions of order to form factors and unitarity of the CKM matrix
The form factors for the semileptonic decay are computed to
order in generalized chiral perturbation theory. The main difference
with the standard expressions consists in contributions quadratic in
quark masses, which are described by a single divergence-free low-energy
constant, . A new simultaneous analysis is presented for the CKM matrix
element , the ratio , decay rates and the
scalar form factor slope . This framework easily accommodates the
precise value for deduced from superallowed nuclear -decays
- …