arXiv subjects
Publications and source records attributed to M. Roth.
The investigation of W-pair production offers unique precision tests of the electroweak theory at future e+e- colliders, including precise determinations of cross sections, the W-boson mass, and gauge-boson self-couplings. The state-of-the-art and future requirements in the theoretical prediction for the reaction e+e- -> WW -> 4f(+gamma) are briefly reviewed.
We present the Monte Carlo generator RacoonWW that computes cross sections to all processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma and calculates the complete O(alpha) electroweak radiative corrections to e^+ e^- -> W W -> 4f in the electroweak Standard Model in double-pole approximation. The calculation of the tree-level processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma is based on the full matrix elements for massless (polarized) fermions. When calculating radiative corrections to e^+ e^- -> W W -> 4f the complete virtual doubly-resonant electroweak corrections are included, i.e. the factorizable and non-factorizable virtual corrections in double-pole approximation, and the real corrections are based on the full matrix elements for e^+ e^- -> 4f + gamma. The matching of soft and collinear singularities between virtual and real corrections is done alternatively in two different ways, namely by using a subtraction method or by applying phase-space slicing. Higher-order initial-state photon radiation and naive QCD corrections are taken into account. RacoonWW also provides anomalous triple gauge-boson couplings for all processes e^+ e^- -> 4f and anomalous quartic gauge-boson couplings for all processes e^+ e^- -> 4f + gamma.
SN 1999aw was discovered during the first campaign of the Nearby Galaxies Supernova Search (NGSS) project. This luminous, slow-declining (Delta m_{15} (B) = 0.81 \pm 0.03) Type Ia supernova was noteworthy in at least two respects. First, it occurred in an extremely low luminosity host galaxy that was not visible in the template images, nor in initial subsequent deep imaging. Secondly, the photometric and spectral properties of this supernova indicate that it very likely was similar to the subclass of Type Ia supernovae whose prototype is SN 1999aa. This paper presents the BVRI and J_{s} HK_{s} lightcurves of SN 1999aw (through 100 days past maximum light), as well as several epochs of optical spectra. From these data we calculate the bolometric light curve, and give estimates of the luminosity at maximum light and the initial ^{56}Ni mass. In addition, we present deep BVI images obtained recently with the Baade 6.5-meter telescope at Las Campanas Observatory which reveal the remarkably low-luminosity host galaxy.
The observation of a small change in spectral slope, or 'knee' in the fluxes of cosmic rays near energies 10^15 eV has caused much speculation since its discovery over 40 years ago. The origin of this feature remains unknown. A small workshop to review some modern experimental measurements of this region was held at the Adler Planetarium in Chicago, USA in June 2000. This paper summarizes the results presented at this workshop and the discussion of their interpretation in the context of hadronic models of atmospheric airshowers.
We discuss the experimental and theoretical uncertainties on precision electroweak observables and their relationship to the indirect constraints on the Higgs-boson mass, $\MH$, in the Standard Model (SM). The critical experimental measurements ($\MW$, $\sweff$, $\mt$, ...) are evaluated in terms of their present uncertainties and their prospects for improved precision at future colliders, and their contribution to the constraints on $\MH$. In addition, the current uncertainties of the theoretical predictions for $\MW$ and $\sweff$ due to missing higher order corrections are estimated and expectations and necessary theoretical improvements for future colliders are explored. The constraints from rare B decays are also discussed. Analysis of the present experimental and theoretical precisions yield a current upper bound on $\MH$ of $\sim 200$ GeV. Including anticipated improvements corresponding to the prospective situation at future colliders (Tevatron Run II, LHC, LC/GigaZ), we find a relative precision of about 25% to 8% (or better) is achievable in the indirect determination of $\MH$.
We discuss theoretical uncertainties of the distribution in the cosine of the W polar angle projected into a measurement of the anomalous triple gauge-boson coupling λ=λ_γ=λ_Z at LEP2 energies for the tandem of the Monte Carlo event generators KoralW and YFSWW3 and for the Monte Carlo event generator RacoonWW. Exploiting numerical results of these programs and cross-checks with experimental fitting procedures, we estimate that the theoretical uncertainty of the value of λdue to electroweak corrections, as obtained at LEP2 with the help of these programs, is ~0.005, about half of the expected experimental error for the combined LEP2 experiments (~0.010). We use certain idealized event selections; however, we argue that these results are valid for realistic LEP2 measurements.
For the envisioned precision measurement of the W-boson mass at present and future lepton and hadron colliders it is crucial that the theoretical predictions for the underlying production processes are well under control. We briefly describe the status of the predictions for the W-pair-production processes at e+ e- colliders, e+ e- -> W+ W- -> 4f, and for W- and Z-boson production at pp and p anti-p colliders, pp, p anti-p -> W -> l nu_l and pp, p anti-p -> Z,gamma -> l+ l- (l=e,mu). We also discuss the theoretical improvements needed to meet the experimental accuracies one hopes to achieve in future experiments.
The relevance of radiative corrections to 4f production at LEP2 and future e+e- colliders is emphasized, and their treatment in the event generator RacoonWW is briefly discussed. In particular, the non-universal corrections are compared with the signature of anomalous triple gauge-boson couplings. For 4f+gamma production the influence of anomalous quartic gauge-boson couplings on photon-energy distributions is illustrated.
We present optical and IR spectroscopy of the first two months of evolution of the Type II SN 1999em. We combine these data with high-quality optical/IR photometry beginning only three days after shock breakout, in order to study the performance of the ``Expanding Photosphere Method'' (EPM) in the determination of distances. With this purpose we develop a technique to measure accurate photospheric velocities by cross-correlating observed and model spectra. The application of this technique to SN 1999em shows that we can reach an average uncertainty of 11% in velocity from an individual spectrum. Our analysis shows that EPM is quite robust to the effects of dust. In particular, the distances derived from the VI filters change by only 7% when the adopted visual extinction in the host galaxy is varied by 0.45 mag. The superb time sampling of the BVIZJHK light-curves of SN 1999em permits us to study the internal consistency of EPM and test the dilution factors computed from atmosphere models for Type II plateau supernovae. We find that, in the first week since explosion, the EPM distances are up to 50% lower than the average, possibly due the presence of circumstellar material. Over the following 65 days, on the other hand, our tests lend strong credence to the atmosphere models, and confirm previous claims that EPM can produce consistent distances without having to craft specific models to each supernova. This is particularly true for the VI filters which yield distances with an internal consistency of 4%. From the whole set of BVIZJHK photometry, we obtain an average distance of 7.5+/-0.5 Mpc, where the quoted uncertainty (7%) is a conservative estimate of the internal precision of the method obtained from the analysis of the first 70 days of the supernova evolution.
All lowest-order amplitudes for e+e- --> 4f+gamma are calculated including five anomalous quartic gauge-boson couplings that are allowed by electromagnetic gauge invariance and the custodial SU(2)_c symmetry. Three of these anomalous couplings correspond to the operators L_0, L_c, and L_n that have been constrained by the LEP collaborations in WWgamma production. The anomalous couplings are incorporated in the Monte Carlo generator RACOONWW. Moreover, for the processes e+e- --> 4f+gamma RACOONWW is improved upon including leading universal electroweak corrections such as initial-state radiation. The discussion of numerical results illustrates the size of the leading corrections as well as the impact of the anomalous quartic couplings for LEP2 energies and at 500GeV.
Electroweak radiative corrections to e+e- scattering processes typically amount to O(10%) at LEP energies. Their logarithmic increase with energy renders them even more important at future colliders. Although the bulk of these corrections is due to universal process-independent effects, the remaining non-universal corrections are nevertheless phenomenologically important. We describe the structure of the universal corrections to e+e- --> WW --> 4f in detail and discuss the numerical size of universal and non-universal effects using the Monte Carlo generator RACOONWW.
We describe the salient features of precise predictions for the processes e+ e- -> WW -> 4f(gamma) as obtained with the Monte Carlo generator RacoonWW, including the complete O(alpha) electroweak radiative corrections in the double-pole approximation. Numerical results for some distributions are given at the typical linear-collider energy \sqrt{s}=500 GeV. Moreover, we study the impact of the non-universal electroweak corrections by comparing with results of an improved Born approximation.
We briefly describe the RacoonWW approach to calculate radiative corrections to e+ e- -> W W -> 4 fermions and present numerical results for the total W-pair production cross section at LEP2.
The complete O(alpha) electroweak radiative corrections to e+e- --> WW --> 4f in the electroweak Standard Model are presented in the double-pole approximation. We give analytical and numerical results for the non-factorizable corrections and express the factorizable virtual corrections in terms of the known corrections to on-shell W-pair production and W decay. The full matrix elements to the lowest order processes e+e- --> 4f+gamma are taken into account for the real corrections. The matching of soft and collinear singularities between virtual and real corrections is done using the subtraction method. A Monte Carlo generator is constructed which corresponds to the subtraction branch of RacoonWW. Various numerical results are presented.
We present precise predictions for the processes e+ e- -> WW -> 4f(gamma) at LEP2 and future Linear-Collider (LC) energies obtained with the Monte Carlo generator RacoonWW. The program RacoonWW includes the complete O(alpha) electroweak radiative corrections to e+ e- -> WW -> 4f in the double-pole approximation (DPA). While the virtual corrections are treated in DPA, the calculation of the bremsstrahlung corrections is based on the full lowest-order matrix elements to the processes e+ e- -> 4f+gamma. This asymmetric treatment of virtual and real photons requires a careful matching of the arising infrared and collinear singularities. We also take into account higher-order initial-state photon radiation via the structure-function method. Here, we briefly describe the RacoonWW approach, give numerical results for the total W-pair production cross sections, confront them with LEP2 data, and study the impact of the radiative corrections on angular and W-invariant-mass distributions at LEP2 and LC energies.
We calculate the complete O(alpha) electroweak radiative corrections to e+e- --> WW --> 4f in the electroweak Standard Model in the double-pole approximation. We give analytical results for the non-factorizable virtual corrections and express the factorizable virtual corrections in terms of the known corrections to on-shell W-pair production and W decay. The calculation of the bremsstrahlung corrections, i.e. the processes e+e- --> 4f+gamma in lowest order, is based on the full matrix elements. The matching of soft and collinear singularities between virtual and real corrections is done alternatively in two different ways, namely by using a subtraction method and by applying phase-space slicing. The O(alpha) corrections as well as higher-order initial-state photon radiation are implemented in the Monte Carlo generator RACOONWW. Numerical results of this program are presented for the W-pair-production cross section, angular and W-invariant-mass distributions at LEP2. We also discuss the intrinsic theoretical uncertainty of our approach.
RACOONWW is the first Monte Carlo generator for e+e- --> WW --> 4f(+gamma) that includes the electroweak O(alpha) radiative corrections in the double-pole approximation completely. Some numerical results for LEP2 energies are discussed, and the predictions for the total W-pair cross section are confronted with LEP2 data.
We present the analysis of morphological and photometric properties of a sample of isolated spirals with (18) and without (11) an active nucleus, based on near-infrared imaging in the J and K' bands. The aim of this analysis is to find the differential properties that could be directly connected with the phenomenon of nuclear activity. We stress the importance of using isolated objects for that purpose. Our study shows that both sets of galaxies are similar in their global properties: they define the same Kormendy relation, their disk components share the same properties, the bulge and disk scale lengths are correlated in a similar way, bar strengths and lengths are similar for primary bars. Hosts of isolated Seyfert galaxies have bulge and disk properties comparable to those of isolated non active spirals. Central colors (the innermost 200 pc) of active galaxies are redder than the centers of non active spirals, most probably due to AGN light being re-emitted by the hot dust and/or due to circumnuclear star formation, through the contribution of giants/supergiants. Only one of the Seyfert galaxies in our sample does not present a primary bar,but both primary and secondary bars are equally present in active and control objects. Secondary central elongations (associated with secondary bars, lenses, rings or disks) may be somewhat different. Numerical models indicate that such secondary bars are not strictly necessary to feed the central engine when a primary bar is present. Our results show that down to scales of 100-300 pc, there are no obvious differences between active and non active spiral galaxies.