172 research outputs found
Unified Dark Matter in Scalar Field Cosmologies
Considering the general Lagrangian of k-essence models, we study and classify
them through variables connected to the fluid equation of state parameter
w_\kappa. This allows to find solutions around which the scalar field describes
a mixture of dark matter and cosmological constant-like dark energy, an example
being the purely kinetic model proposed by Scherrer. Making the stronger
assumption that the scalar field Lagrangian is exactly constant along solutions
of the equation of motion, we find a general class of k-essence models whose
classical trajectories directly describe a unified dark matter/dark energy
(cosmological constant) fluid. While the simplest case of a scalar field with
canonical kinetic term unavoidably leads to an effective sound speed c_s=1,
thereby inhibiting the growth of matter inhomogeneities, more general
non-canonical k-essence models allow for the possibility that c_s << 1 whenever
matter dominates
Cosmic Microwave Background Anisotropies up to Second Order
These lecture notes present the computation of the full system of Boltzmann
equations describing the evolution of the photon, baryon and cold dark matter
fluids up to second order in perturbation theory, as recently studied in
(Bartolo, Matarrese & Riotto 2006, 2007). These equations allow to follow the
time evolution of the cosmic microwave background anisotropies at all angular
scales from the early epoch, when the cosmological perturbations were
generated, to the present, through the recombination era. The inclusion of
second-order contributions is mandatory when one is interested in studying
possible deviations from Gaussianity of cosmological perturbations, either of
primordial (e.g. inflationary) origin or due to their subsequent evolution.
Most of the emphasis in these lectures notes will be given to the derivation of
the relevant equations for the study of cosmic microwave background
anisotropies and to their analytical solutions
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
Spectroscopy of Low Energy Neutrinos from the Sun
Two methods are discussed for the solar neutrino spectroscopy in the sub-MeV
region: absorption in a loaded liquid scintillator and elastic scattering in a
TPC. The different neutrino oscillation solutions predict a strong effect in
this energy region where the largest fraction (\sim 98%) of solar neutrinos
lies. Both projects have reached the stage where they have to prove their
capability to attain a background low enough for solar neutrino detection
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
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
B-mode polarization of the CMB from the second-order photon quadrupole
We study a new contribution to the polarization of the Cosmic Microwave
Background induced at the epoch of recombination by the second-order quadrupole
moment of the photon distribution. At second order in perturbation theory the
quadrupole moment is not suppressed by the inverse of the optical depth in the
tight coupling limit, as it happens at first order in perturbation theory. We
concentrate on the B-mode CMB polarization and find that such a novel
contribution constitutes a contamination in the detection of the primordial
tensor modes if the tensor to scalar ratio r is smaller than a few x 10^{-5}.
The magnitude of the effect is larger than the B-mode due to secondary
vector/tensor perturbations and the analogous effect generated during the
reionization epoch, while it is smaller than the contamination produced by the
conversion of polarization of type E into type B, by weak gravitational
lensing. However the lensing signal can be cleaned, making the secondary modes
discussed here the actual contamination limiting the detection of small
amplitude primordial gravitational waves if r is below \simeq 10^{-5}
|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
Order and anarchy hand in hand in 5D SO(10)
We update a five-dimensional SO(10) grand unified model of fermion masses and mixing angles originally proposed by Kitano and Li. In our setup Yukawa couplings are anarchical and quark and lepton sectors are diversified by the profiles of the fermion zero modes in the extra dimension. The breaking of SO(10) down to SU(5)×U(1) X provides the key parameter that distinguishes the profiles of the different SU(5) components inside the same 16 representation. With respect to the original version of the model, we extend the Higgs sector to explicitly solve the doublet-triplet splitting problem through the missing partner mechanism and we perform a fit to an idealized set of data. By scanning the Yukawa couplings of the model we find that, for large tan β , both normal and inverted ordered neutrino spectrum can be accommodated. However, while the case of inverted order requires a severe fine tuning of the Yukawa parameters, the normal ordering is compatible with an anarchical distribution of Yukawa couplings. Thus, in a natural portion of the parameter space, the model predicts a normal ordered neutrino spectrum, the lightest neutrino mass below 5 meV, and | m ββ | in the range 0.1-5 meV. No particular preference is found for the Dirac CP phase in the lepton sector while the right-handed neutrino masses are too small to explain the baryon asymmetry of the universe through thermal leptogenesis
An Equivalent Gauge and the Equivalence Theorem
I describe a novel covariant formulation of massive gauge theories in which the longitudinal polarization vectors do not grow with the energy. Therefore in the present formalism, differently from the ordinary one, the energy and coupling power-counting is completely transparent at the level of individual Feynman diagrams, with obvious advantages both at the conceptual and practical level
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