218 research outputs found
The piNNN--NNN problem. Connectedness, transition amplitudes and quasi-particle approximation
In this paper we review the present status of the piNNN--NNN problem. In
particular, we re-consider the chain-labelled approach recently proposed by us,
and identify a class of graphs, previously overlooked, which prevents the
kernel of the corresponding piNNN--NNN equations from being connected. We
propose some pproximate schemes, yielding connected-kernel equations. A
generalization of the residue method allows to relate the transition amplitudes
for the coupled piNNN--NNN system to the chain-labelled formalism. The
quasi-particle approach is extended to the present situation, where
emission/absorption of particles is allowed. The open problems for the
piNNN--NNN system in the light of the present and of previous approaches are
finally discussed
Second-Order Cosmological Perturbations from Inflation
We present the first computation of the cosmological perturbations generated
during inflation up to second order in deviations from the homogeneous
background solution. Our results, which fully account for the inflaton
self-interactions as well as for the second-order fluctuations of the
background metric, provide the exact expression for the gauge-invariant
curvature perturbation bispectrum produced during inflation in terms of the
slow-roll parameters or, alternatively, in terms of the scalar spectral
and and the tensor to adiabatic scalar amplitude ratio . The bispectrum
represents a specific non-Gaussian signature of fluctuations generated by
quantum oscillations during slow-roll inflation. However, our findings indicate
that detecting the non-Gaussianity in the cosmic microwave background
anisotropies emerging from the second-order calculation will be a challenge for
the forthcoming satellite experiments
A novel architecture for DAQ in multi-channel, large volume, long drift Liquid Argon TPC
Recently a large interest has been shown for multi-ton Liquid Argon
Time-Projection-Chambers (LAr-TPC). The physics issues are very challenging,
but the technical problem of long drifts and adequately long life-time of free
electrons are not solved at all so far. Also one should take into account the
extremely large number of channels required for such large volumes. In this
paper we propose an architecture for DAQ that is based on recent developments
in consumer electronics that made available, at a quite interesting price,
components aimed to high-resolution delta-sigma conversion. This type of ADC is
not at all popular in HEP experiments where normally signals related to events,
well defined in time (triggered), should be converted and recorded. In the
LAr-TPC however we have to deal rather with waveforms that should be converted
and recorded continuously, that is the paramount case of delta-sigma ADC
application
A decade of dark matter searches with ground-based Cherenkov telescopes
In the general scenario of Weakly Interacting Massive Particles (WIMP), dark
matter (DM) can be observed via astrophysical gamma rays because photons are
produced in various DM annihilation or decay processes, either as broad-band or
line emission, or because of the secondary processes of charged particles in
the final stages of the annihilations or the decays. The energy range of the
former processes is accessible by current ground-based Imaging Atmospheric
Cherenkov telescopes (IACTs, like H.E.S.S., MAGIC and VERITAS). The strengths
of this technique are: a) the expected DM gamma-ray spectra show peculiar
features like bumps, spikes and cutoff that make them clearly distinguishable
from the smoother astrophysical spectra, b) the expected DM spectrum is
universal and therefore by observing two or more DM targets with the same
spectrum, a clear identification (besides detection) of DM would be enabled.
The role of IACTs may gain more importance in the future as the results from
the LHC may hint to a DM particle with mass at the TeV or above, where the
IACTs sensitivity is unsurpassed by other experiments. In this contribution, a
review of the search for DM with the current generation of IACT will be
presented
Possibly Large Corrections to the Inflationary Observables
We point out that the theoretical predictions for the inflationary
observables may be generically altered by the presence of fields which are
heavier than the Hubble rate during inflation and whose dynamics is usually
neglected. They introduce corrections which may be easily larger than both the
second-order contributions in the slow-roll parameters and the accuracy
expected in the forthcoming experiments
Supersymmetry and Brane Cosmology
We consider a five-dimensional brane world scenario where the fifth dimension
is compactified on . We show that the familiar four-dimensional
cosmology on our brane is easily recovered during a primordial stage of
inflation if supersymmetry is exploited. Even if some vacuum energy density
appears localized on our three brane, heavy supersymmetric bulk fields adjust
themselves and acquire a nontrivial configuration along the extra-dimension.
This phenomenon redistributes uniformly the energy density across the bulk and
the resulting energy-momentum tensor does not display any singularity
associated to the initial localized energy density on our three-brane. No jumps
across the brane are present for the derivatives of the metric and Einstein's
equations are solved by constant solutions along the fifth dimension. Our
findings make it clear that cosmological phenomena in the supersymmetric brane
world scenario must be studied taking properly into account bulk supersymmetric
states. This comment is particularly relevant when applied to (super)gravity
since in supersymmetric brane world scenarios, even though chiral matter and
gauge fields may be restricted to live on boundaries, gravity multiplets always
propagate in the bulk
Critical Behavior in Peripheral Au + Au Collisions at 35 MeV/u
The signals theoretically predicted for the occurrence of a critical behavior
(conditional moments of charge distributions, Campi scatter plot, fluctuations
of the size of the largest fragment, power law in the charge distribution,
intermittency) have been found for peripheral events in the reaction Au+Au at
35 MeV/u. The same signals have been studied with a dynamical model which
foresees phase transition, like the Classical Molecular Dynamics
Superfield theories on S 3 and their localization
We consider the superfield formulation of supersymmetric gauge and matter field theories on a three-dimensional sphere with rigid = 2 supersymmetry, as well as with > 2. The construction is based on a supercoset SU(2 | 1)/U(1) containing S 3 as the bosonic subspace. We derive an explicit form of SU(2 | 1)/U(1) supervielbein and covariant derivatives, and use them to construct classical superfield actions for gauge and matter supermultiplets in this superbackground. We then apply superfield methods for computing one-loop partition functions of these theories and demonstrate how the localization technique works directly in the superspace
|q/p| Measurement from B0->D*l nu Partial Reconstruction
We present a new measurement of CP violation induced by B0 B0bar
oscillations, based on the full data set collected by the BaBar experiment at
the PEPII collider. We use a sample of about 6 million B0->D* l nu decays
selected with partial reconstruction of the D* meson. The charged lepton
identifies the flavor of the first B meson at its decay time, the flavor of the
other B is determined by kaon tagging. We determine the parameter dCP = 1 -
|q/p| = (0.29+-0.84+1.78/-1.61) 10^-3
On the Effective Electron Mass in Magnetar-like Fields
We show, either quantum mechanically or classically, that the variation of
the effective mass induced in a charged particle by the presence of an
ultra-strong electromagnetic field may lead to observable consequences. In
particular, we discuss how this effect may operate on electrons close to the
surface of a magnetar, a neutron star with a super-strong magnetic field of the
order of Tesla
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