5,834 research outputs found

### Soft Colour Interactions and Diffractive DIS

The basic ideas and some results of the semiclassical approach to diffractive
DIS are briefly described. In the production of high-$p_{\perp}$ jets
boson-gluon fusion is predicted to be the dominant partonic process. The
$p_{\perp}$-spectrum and the two-jet invariant mass distribution provide a
clear test of the underlying `hard' partonic process and the `soft' mechanism
of colour neutralization.Comment: 6 pages, proceedings DIS 9

### Classical Limit for Scalar Fields at High Temperature

We study real-time correlation functions in scalar quantum field theories at
temperature $T=1/\beta$. We show that the behaviour of soft, long wavelength
modes is determined by classical statistical field theory. The loss of quantum
coherence is due to interactions with the soft modes of the thermal bath. The
soft modes are separated from the hard modes by an infrared cutoff \L \ll
1/(\hbar\beta). Integrating out the hard modes yields an effective theory for
the soft modes. The infrared cutoff \L controls corrections to the classical
limit which are \cO{\hbar\beta\L}. As an application, the plasmon damping
rate is calculated.Comment: 24 pages, 7 eps figures, Late

### Calculating the diffractive from the inclusive structure function

It is demonstrated that the global properties of the rapidity gap events at
HERA can be understood based on electron-gluon scattering and a
non-perturbative mechanism of colour neutralization. Using the measured
inclusive structure function $F_2$ to determine the parameters of the parton
model, the diffractive structure function $F_2^D$ is predicted. The ratio of
diffractive and inclusive cross sections, $R_D = \sigma_D/\sigma_{incl}\simeq
1/9$, is determined by the probability of the produced quark-antiquark pair to
evolve into a colour singlet state.Comment: talk at Workshop on DIS and QCD, Paris, April 1995, 3 pages LaTeX,
uses qcdparis.sty, 2 figures (uuencoded

### Neutrino Physics (theory)

Nonzero neutrino masses are the first definitive need to extend the standard
model. After reviewing the basic framework, I describe the status of some of
the major issues, including tests of the basic framework of neutrino masses and
mixings; the question of Majorana vs. Dirac; the spectrum, mixings, and number
of neutrinos; models, with special emphasis on constraints from typical
superstring constructions (which are not consistent with popular bottom-up
assumptions); and other implications.Comment: 13 pages, 6 figures, invited plenary talk at ICHEP200

### The Chaotic Regime of D-Term Inflation

We consider D-term inflation for small couplings of the inflaton to matter
fields. Standard hybrid inflation then ends at a critical value of the inflaton
field that exceeds the Planck mass. During the subsequent waterfall transition
the inflaton continues its slow-roll motion, whereas the waterfall field
rapidly grows by quantum fluctuations. Beyond the decoherence time, the
waterfall field becomes classical and approaches a time-dependent minimum,
which is determined by the value of the inflaton field and the self-interaction
of the waterfall field. During the final stage of inflation, the effective
inflaton potential is essentially quadratic, which leads to the standard
predictions of chaotic inflation. The model illustrates how the decay of a
false vacuum of GUT-scale energy density can end in a period of `chaotic
inflation'.Comment: 15 pages, 6 figures. v3: matches version published in JCA

### The Neutrino Mass Window for Baryogenesis

Interactions of heavy Majorana neutrinos in the thermal phase of the early
universe may be the origin of the cosmological matter-antimatter asymmetry.
This mechanism of baryogenesis implies stringent constraints on light and heavy
Majorana neutrino masses. We derive an improved upper bound on the CP asymmetry
in heavy neutrino decays which, together with the kinetic equations, yields an
upper bound on all light neutrino masses of 0.1 eV. Lepton number changing
processes at temperatures above the temperature T_B of baryogenesis can erase
other, pre-existing contributions to the baryon asymmetry. We find that these
washout processes become very efficient if the effective neutrino mass
\tilde{m}_1 is larger than m_* \simeq 10^{-3} eV. All memory of the initial
conditions is then erased. Hence, for neutrino masses in the range from (\Delta
m^2_sol)^{1/2} \simeq 8*10^{-3} eV to (\Delta m^2_atm)^{1/2} \simeq 5*10^{-2}
eV, which is suggested by neutrino oscillations, leptogenesis emerges as the
unique source of the cosmological matter-antimatter asymmetry.Comment: 29 pages, 12 figures include

### Some Aspects of Thermal Leptogenesis

Properties of neutrinos may be the origin of the matter-antimatter asymmetry
of the universe. In the seesaw model for neutrino masses this leads to
important constraints on the properties of light and heavy neutrinos. In
particular, an upper bound on the light neutrino masses of 0.1 eV can be
derived. We review the present status of thermal leptogenesis with emphasis on
the theoretical uncertainties and discuss some implications for lepton and
quark mass hierarchies, CP violation and dark matter. We also comment on the
`leptogenesis conspiracy', the remarkable fact that neutrino masses may lie in
the range where leptogenesis works best.Comment: 23 pages, 5 figures, submitted to the Focus on Neutrino Physics issue
of the New Journal of Physics, edited by F. Halzen, M. Lindner and A. Suzuk

### Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses

We study the implications of thermal leptogenesis for neutrino parameters.
Assuming that decays of N_1, the lightest of the heavy Majorana neutrinos,
initiate baryogenesis, we show that the final baryon asymmetry is determined by
only four parameters: the CP asymmetry epsilon_1, the heavy neutrino mass M_1,
the effective light neutrino mass \tilde{m}_1, and the quadratic mean \bar{m}
of the light neutrino masses. Imposing the CMB measurement of the baryon
asymmetry as constraint on the neutrino parameters, we show, in a model
independent way, that quasi-degenerate neutrinos are incompatible with thermal
leptogenesis. For maximal CP asymmetry epsilon_1, and neutrino masses in the
range from (\Delta m^2_{sol})^{1/2} to (\Delta m^2_{atm})^{1/2}, the
baryogenesis temperature is T_B = O(10^{10}) GeV.Comment: 28 pages, 14 figures included; v2: erratum added, M_1 lower bound in
the strong wash-out regime (see Eq. (63)) relaxed by a factor 2/

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