Model dependence of single-energy fits to pion photoproduction data

Model dependence of multipole analysis has been explored through energy-dependent and single-energy fits to pion photoproduction data. The MAID energy-dependent solution has been used as input for an event generator producing realistic pseudo data. These were fitted using the SAID parametrization approach to determine single-energy and energy-dependent solutions over a range of lab photon energies from 200 to 1200 MeV. The resulting solutions were found to be consistent with the input amplitudes from MAID. Fits with a $\chi$-squared per datum of unity or less were generally achieved. We discuss energy regions where consistent results are expected, and explore the sensitivity of fits to the number of included single- and double-polarization observables. The influence of Watson's theorem is examined in detail.Comment: 12 pages, 8 figure

Magnetic moments of the low-lying JP= 1/2−J^P=\,1/2^-, 3/2−3/2^- Λ\Lambda resonances within the framework of the chiral quark model

The magnetic moments of the low-lying spin-parity $J^P=$ $1/2^-$, $3/2^-$ $\Lambda$ resonances, like, for example, $\Lambda(1405)$ $1/2^-$, $\Lambda(1520)$ $3/2^-$, as well as their transition magnetic moments, are calculated using the chiral quark model. The results found are compared with those obtained from the nonrelativistic quark model and those of unitary chiral theories, where some of these states are generated through the dynamics of two hadron coupled channels and their unitarization

Constraining the Detailed Balance Condition in Horava Gravity with Cosmic Accelerating Expansion

In 2009 Ho\v{r}ava proposed a power-counting renormalizable quantum gravity theory. Afterwards a term in the action that softly violates the detailed balance condition has been considered with the attempt of obtaining a more realistic theory in its IR-limit. This term is proportional to $\omega R^{(3)}$, where $\omega$ is a constant parameter and $R^{(3)}$ is the spatial Ricci scalar. In this paper we derive constraints on this IR-modified Ho\v{r}ava theory using the late-time cosmic accelerating expansion observations. We obtain a lower bound of $|\omega|$ that is nontrivial and depends on $\Lambda_W$, the cosmological constant of the three dimensional spatial action in the Ho\v{r}ava gravity. We find that to preserve the detailed balance condition, one needs to fine-tune $\Lambda_W$ such that - 2.29\times 10^{-4}< (c^2 \Lambda_W)/(H^2_0 \currentDE) - 2 < 0 , where $H_0$ and \currentDE are the Hubble parameter and dark energy density fraction in the present epoch, respectively. On the other hand, if we do not insist on the detailed balance condition, then the valid region for $\Lambda_W$ is much relaxed to -0.39< (c^2 \Lambda_W)/(H^2_0 \currentDE) - 2 < 0.12. We find that although the detailed balance condition cannot be ruled out, it is strongly disfavored.Comment: 22 pages with 7 figures, references adde

Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector

We study the S-wave interaction of mesons with baryons in the strangeness S=0 sector in a coupled channel unitary approach. The basic dynamics is drawn from the lowest order meson baryon chiral Lagrangians. Small modifications inspired by models with explicit vector meson exchange in the t-channel are also considered. In addition the pi pi N channel is included and shown to have an important repercussion in the results, particularly in the isospin 3/2 sector.Comment: 23 pages, LaTeX, 21 figure

Charmless hadronic decays B→PP,PV,VVB \to PP, PV, VV and new physics effects in the general two-Higgs doublet models

Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to the branching ratios of the two-body charmless hadronic decays of $B_u$ and $B_d$ mesons induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs doublet models (models I, II and III). Within the considered parameter space, we find that: (a) the new physics effects from new gluonic penguin diagrams strongly dominate over those from the new $\gamma$- and $Z^0$- penguin diagrams; (b) in models I and II, new physics contributions to most studied B meson decay channels are rather small in size: from -15% to 20%; (c) in model III, however, the new physics enhancements to the penguin-dominated decay modes can be significant, $\sim (30 -200)$, and therefore are measurable in forthcoming high precision B experiments; (d) the new physics enhancements to ratios {\cal B}(B \to K \etap) are significant in model III, $\sim (35 -70)$, and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large B \to K \etap decay rates; (e) the theoretical predictions for ${\cal B}(B \to K^+ \pi)$ and ${\cal B}(B \to K^0 \pi^+)$ in model III are still consistent with the data within $2\sigma$ errors; (f) the significant new physics enhancements to the branching ratios of $B \to K^0 \pi^0, K^* \eta, K^{*+} \pi^-, K^+ \phi, K^{*0} \omega, K^{*+} \phi$ and $K^{*0} \phi$ decays are helpful to improve the agreement between the data and the theoretical predictions; (g) the theoretical predictions of ${\cal B}(B \to PP, PV, VV)$ in the 2HDM's are generally consistent with experimental measurements and upper limits ($90$)Comment: 55 pages, Latex file, 17 PS and EPS figures. With minor corrections, final version to be published in Phys.Rev. D. Repot-no: PKU-TH-2000-4

P-wave excited baryons from pion- and photo-induced hyperon production

We report evidence for $N(1710)P_{11}$, $N(1875)P_{11}$, $N(1900)P_{13}$, $\Delta(1600)P_{33}$, $\Delta(1910)P_{31}$, and $\Delta(1920)P_{33}$, and find indications that $N(1900)P_{13}$ might have a companion state at 1970\,MeV. The controversial $\Delta(1750)P_{31}$ is not seen. The evidence is derived from a study of data on pion- and photo-induced hyperon production, but other data are included as well. Most of the resonances reported here were found in the Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were challenged recently by the Data Analysis Center at GWU. Our analysis is constrained by the energy independent $\pi N$ scattering amplitudes from either KH84 or GWU. The two $\pi N$ amplitudes from KH84 or GWU, respectively, lead to slightly different $\pi N$ branching ratios of contributing resonances but the debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde

Magnetic moments of the low-lying {1/2}^- octet baryon resonances

The magnetic moments of the negative parity octet resonances with spin {1/2}: $N^*$(1535), $N^*$(1650), $\Sigma^*$(1620), and $\Xi^*$(1690) have been calculated within the framework of the chiral constituent quark model. In this approach, the presence of the polarized $q\bar{q}$ pairs (or the meson cloud, in other words) is considered by using the Lagrangian for Goldstone boson emission from the constituent quarks. Further, the explicit contributions coming from the spin and orbital angular momentum, including the effects of the configurations mixing between the states with different spins, are obtained. The motivation for these calculations comes from the recent interest in experimental measurement of the magnetic moment of the ${S_{11}(1535)}$ resonance and of similar calculations being done within lattice quantum chromodynamics approaches. Our results can be compared with those expected to come from these sources.Comment: 17 pages, 2 table

Tests of AMiBA Data Integrity

We describe methods used to validate data from the Y.T. Lee Array for Microwave Background Anisotropy (AMiBA), an interferometric array designed to measure the Sunyaev-Zel'dovich effect and the anisotropy of the Cosmic Microwave Background (CMB). We perform several statistical tests on data from pointed galaxy cluster observations taken in 2007 and noise data from long-term blank sky observations and measurements with the feeds covered by the absorbers. We apply power spectrum analysis, cross power spectrum analysis among different outputs with different time lags in our analog correlator, and sample variance law tests to noise data. We find that (1) there is no time variation of electronic offsets on the time scale of our two-patch observations (~10 minutes); (2) noise is correlated by less than 10% between different lags; and (3) the variance of noise scales with the inverse of time. To test the Gaussianity of the data, we apply Kolmogorov-Smirnov (K-S) tests to cluster data, and find that a 5% significance level efficiently detects data sets with known hardware problems without rejecting an excess of acceptable data. We also calculate third- and fourth-order moments and cumulants for the noise residual visibilities and find that about 95% of our data are within the 99% confidence regions of Gaussianity.Comment: 15 pages, 5 figures, accepted for publication in Ap

AMiBA: System Performance

The Y.T. Lee Array for Microwave Background Anisotropy (AMiBA) started scientific operation in early 2007. This work describes the optimization of the system performance for the measurements of the Sunyaev-Zel'dovich effect for six massive galaxy clusters at redshifts $0.09 - 0.32$. We achieved a point source sensitivity of $63\pm 7$ mJy with the seven 0.6m dishes in 1 hour of on-source integration in 2-patch differencing observations. We measured and compensated for the delays between the antennas of our platform-mounted interferometer. Beam switching was used to cancel instrumental instabilities and ground pick up. Total power and phase stability were good on time scales of hours, and the system was shown to integrate down on equivalent timescales of 300 hours per baseline/correlation, or about 10 hours for the entire array. While the broadband correlator leads to good sensitivity, the small number of lags in the correlator resulted in poorly measured bandpass response. We corrected for this by using external calibrators (Jupiter and Saturn). Using Jupiter as the flux standard, we measured the disk brightness temperature of Saturn to be $149^{+5}_{-12}$ K.Comment: 9 pages, 7 figures, 1 table, accepted for publication in Ap