We search for neutral heavy leptons that are isosinglets under the standard SU (2)l gauge group. Such neutral heavy leptons are expected in many extensions of the standard model. Three types of heavy leptons Ne, N^, NT associated with the three neutrino types v* have been directly searched for and no evidence for a signal has been found. We set the limit Br(Z° -► z//N*) < 3 x 10" 5 at the 95% CL for the mass range from 3 GeV up to m%.

L

The ⌬ 4,5 double bond was missing in two of the structures shown in Fig. 21 of both the Papers in Press and the published version of this manuscript (structures of 16␣-hydroxyprogesterone and 21-hydroxyprogesterone). These oxidation products had already been identified in the work presented in Refs. 7 and 53, as cited, and had not been first identified in this work. This error has now been corrected and does not affect the results or conclusions of this work.

The QCD axion serves as a well-motivated dark matter candidate and the misalignment mech-

Reheating is a process where the energy density of a dominant component of the universe other than radiation, such as a matter component, is transferred into radiation. It is usually assumed that the temperature of the universe decreases due to cosmic expansion even during the reheating process, in which case the maximal temperature of the universe is much higher than the reheat temperature. We point out that the temperature of the universe during reheating may in fact increase in well-motivated scenarios. We derive the necessary conditions for the temperature to increase during reheating and discuss concrete examples involving a scalar field. We comment on implications for particle physics and cosmology due to an increasing temperature during reheating.

No abstract

We present a study of 43 000 3-jet events from Z° boson decays. Both the measured jet energy distributions and the event orientation are reproduced by second order QCD. An alternative model with scalar gluons fails to describe the data.

Several theoretical motivations point to ultralight QCD axions with large decay constants f a O(10 16 -10 17 ) GeV, to which experimental proposals are dedicated. This regime is known to face the problem of overproduction of axion dark matter from the misalignment mechanism unless the misalignment angle θ mis is as small as O(10 −3 -10 −4 ), which is generally considered a finetuning problem. We investigate a dynamical explanation for a small θ mis . The axion mass arises from strong dynamics and may be sufficiently enhanced by early dynamics so as to overcome Hubble friction and drive the field value to the bottom of the potential long before the QCD phase transition. Together with an approximate CP symmetry in the theory, this minimum is very closely related to today's value and thus θ mis can automatically be well under unity. Owing to such efficient relaxation, the isocurvature perturbations are essentially damped. As an existence proof, using supersymmetric theories we illustrate that the Higgs coupling with the inflaton energy can successfully achieve this axion damping in a consistent inflationary cosmology.