The High Altitude Water Cherenkov (HAWC) observatory is an array of large water Cherenkov detectors sensitive to gamma rays and hadronic cosmic rays in the energy band between 100 GeV and 100 TeV. The observatory will be used to measure high-energy protons and cosmic rays via detection of the energetic secondary particles reaching the ground when one of these particles interacts in the atmosphere above the detector. HAWC is under construction at a site 4100 meters above sea level on the northern slope of the volcano Sierra Negra, which is located in central Mexico at 19• N latitude. It is scheduled for completion in 2014. In this paper we estimate the sensitivity of the HAWC instrument to point-like and extended sources of gamma rays. The source fluxes are modeled using both unbroken power laws and power laws with exponential cutoffs. HAWC, in one year, is sensitive to point sources with integral powerlaw spectra as low as 5 × 10 −13 cm −2 sec −1 above 2 TeV (approximately 50 mCrab) over 5 sr of the sky. This is a conservative estimate based on simple event parameters and is expected to improve as the data analysis techniques are refined. We discuss known TeV sources and the scientific contributions that HAWC can make to our understanding of particle acceleration in these sources.

We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn could help to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles

The goal of the present analysis is to find, in the free neutron beta decay, the expressions for the decay rate and the electron asymmetry that contain all the theoretical effects at the 10−4 level. This accuracy is better than the current experimental precision that modern experiments allow. For this aim it is necessary to study the strong interaction effects, the radiative corrections and the recoil of the proton. A conceptual problem that we discuss in detail is the Fermi function additivity. The model dependence in the radiative corrections yields important effects which must be incorporated. We show that this is the only source of uncertainty that is out of control still at the mentioned order. As an application, we compare the values of the CKM matrix element |Vud | from this decay with the values both from the superallowed Fermi transition beta decays and the unitarity of the CKM matrix. We discuss the relevance of the observed discrepancies.

Measurements of neutron beta decay observables required to determine |V ud | are reaching the 0.1% accuracy. In this paper we review the calculation of the decay rate of this process, discuss its relevant uncertainties, and obtain an expression that is precise at the 10 −4 level. Our analysis clearly shows the necessity of more precise measurements of λ, the ratio of axial/vector couplings. The current situation in neutron beta decay is that one cannot yet quote a single consistent value for |V ud | from it. We also discuss the region of parameter space in the |V ud |-λ plane where new physics effects should lie, if they contribute to neutron beta decay.

Static quantities of the W boson in the SU L (3) × U X (1) model with right-handed neutrinos The static electromagnetic properties of the W boson, ∆κ and ∆Q, are calculated in the SUL(3)× UX (1) model with right-handed neutrinos. The new contributions from this model arise from the gauge and scalar sectors. In the gauge sector there is a new contribution from a complex neutral gauge boson Y 0 and a singly-charged gauge boson Y ± . The mass of these gauge bosons, called bileptons, is expected to be in the range of a few hundreds of GeV according to the current bounds from experimental data. If the bilepton masses are of the order of 200 GeV, the size of their contribution is similar to that obtained in other weakly coupled theories. However the contributions to both ∆Q and ∆κ are negligible for very heavy or degenerate bileptons. As for the scalar sector, an scenario is examined in which the contribution to the W form factors is identical to that of a two-Higgs-doublet model. It is found that this sector would not give large corrections to ∆κ and ∆Q.