698 research outputs found
Three Dimensional N=2 Supersymmetry on the Lattice
We show how 3-dimensional, N=2 supersymmetric theories, including super QCD
with matter fields, can be put on the lattice with existing techniques, in a
way which will recover supersymmetry in the small lattice spacing limit.
Residual supersymmetry breaking effects are suppressed in the small lattice
spacing limit by at least one power of the lattice spacing a.Comment: 21 pages, 2 figures, typo corrected, reference adde
Beam instrumentation for the Tevatron Collider
The Tevatron in Collider Run II (2001-present) is operating with six times
more bunches and many times higher beam intensities and luminosities than in
Run I (1992-1995). Beam diagnostics were crucial for the machine start-up and
the never-ending luminosity upgrade campaign. We present the overall picture of
the Tevatron diagnostics development for Run II, outline machine needs for new
instrumentation, present several notable examples that led to Tevatron
performance improvements, and discuss the lessons for future colliders
Modified Gravity via Spontaneous Symmetry Breaking
We construct effective field theories in which gravity is modified via
spontaneous breaking of local Lorentz invariance. This is a gravitational
analogue of the Higgs mechanism. These theories possess additional graviton
modes and modified dispersion relations. They are manifestly well-behaved in
the UV and free of discontinuities of the van Dam-Veltman-Zakharov type,
ensuring compatibility with standard tests of gravity. They may have important
phenomenological effects on large distance scales, offering an alternative to
dark energy. For the case in which the symmetry is broken by a vector field
with the wrong sign mass term, we identify four massless graviton modes (all
with positive-definite norm for a suitable choice of a parameter) and show the
absence of the discontinuity.Comment: 5 pages; revised versio
Energy Budget of Cosmological First-order Phase Transitions
The study of the hydrodynamics of bubble growth in first-order phase
transitions is very relevant for electroweak baryogenesis, as the baryon
asymmetry depends sensitively on the bubble wall velocity, and also for
predicting the size of the gravity wave signal resulting from bubble
collisions, which depends on both the bubble wall velocity and the plasma fluid
velocity. We perform such study in different bubble expansion regimes, namely
deflagrations, detonations, hybrids (steady states) and runaway solutions
(accelerating wall), without relying on a specific particle physics model. We
compute the efficiency of the transfer of vacuum energy to the bubble wall and
the plasma in all regimes. We clarify the condition determining the runaway
regime and stress that in most models of strong first-order phase transitions
this will modify expectations for the gravity wave signal. Indeed, in this
case, most of the kinetic energy is concentrated in the wall and almost no
turbulent fluid motions are expected since the surrounding fluid is kept mostly
at rest.Comment: 36 pages, 14 figure
Thermal production of ultrarelativistic right-handed neutrinos: Complete leading-order results
The thermal production of relativistic right-handed Majorana neutrinos is of
importance for models of thermal leptogenesis in the early Universe.
Right-handed neutrinos can be produced both by 1 2 decay or inverse decay
and by 2 -> 2 scattering processes. In a previous publication, we have studied
the production via 1 2 (inverse) decay processes. There we have shown that
multiple scattering mediated by soft gauge boson exchange also contributes to
the production rate at leading order, and gives a strong enhancement. Here we
complete the leading order calculation by adding 2 -> 2 scattering processes
involving either electroweak gauge bosons or third-generation quarks. We find
that processes with gauge interactions give the most important contributions.
We also obtain a new sum rule for the Hard Thermal Loop resummed fermion
propagator.Comment: 27 pages, 7 figures. Error in the matrix element for the
(subdominant) subprocess with s-channel fermion exchange corrected. This
changes the corresponding phase space integral and the constant c_V.
Numerically it increases the total 2 -> 2 rate by about 2 percent and the
complete rate by about 1 percent. The main results and conclusions are
unaffecte
Confusing the extragalactic neutrino flux limit with a neutrino propagation limit
We study the possible suppression of the extragalactic neutrino flux due to a
nonstandard interaction during its propagation. In particular, we study
neutrino interaction with an ultra-light scalar field dark matter. It is shown
that the extragalactic neutrino flux may be suppressed by such an interaction,
leading to a new mechanism to reduce the ultra-high energy neutrino flux. We
study both the cases of non-self-conjugate as well as self-conjugate dark
matter. In the first case, the suppression is independent of the neutrino and
dark matter masses. We conclude that care must be taken when explaining limits
on the neutrino flux through source acceleration mechanisms only, since there
could be other mechanisms for the reduction of the neutrino flux.Comment: 15 pages, 4 figures. Important changes implemented. Abstract
modified. Conclusions remain. To be published in JCA
- …