44 research outputs found
Soft leptogenesis in the inverse seesaw model
We consider leptogenesis induced by soft supersymmetry breaking terms ("soft
leptogenesis"), in the context of the inverse seesaw mechanism. In this model
there are lepton number (L) conserving and L-violating soft
supersymmetry-breaking B-terms involving the singlet sneutrinos which, together
with the -- generically small-- L-violating parameter responsible of the
neutrino mass, give a small mass splitting between the four singlet sneutrino
states of a single generation. In combination with the trilinear soft
supersymmetry breaking terms they also provide new CP violating phases needed
to generate a lepton asymmetry in the singlet sneutrino decays. We obtain that
in this scenario the lepton asymmetry is proportional to the L-conserving soft
supersymmetry-breaking B-term, and it is not suppressed by the L-violating
parameters. Consequently we find that, as in the standard see-saw case, this
mechanism can lead to sucessful leptogenesis only for relatively small value of
the relevant soft bilinear coupling. The right-handed neutrino masses can be
sufficiently low to elude the gravitino problem. Also the corresponding Yukawa
couplings involving the lightest of the right-handed neutrinos are constrained
to be \sum |Y_{1k}|^2\lesssim 10^{-7} which generically implies that the
neutrino mass spectrum has to be strongly hierarchical.Comment: 28 pages, 1 figure; some references added; final version to appear in
JHE
Leptogenesis from Soft Supersymmetry Breaking (Soft Leptogenesis)
Soft leptogenesis is a scenario in which the cosmic baryon asymmetry is
produced from a lepton asymmetry generated in the decays of heavy sneutrinos
(the partners of the singlet neutrinos of the seesaw) and where the relevant
sources of CP violation are the complex phases of soft supersymmetry-breaking
terms. We explain the motivations for soft leptogenesis, and review its basic
ingredients: the different CP-violating contributions, the crucial role played
by thermal corrections, and the enhancement of the efficiency from lepton
flavour effects. We also discuss the high temperature regime GeV in
which the cosmic baryon asymmetry originates from an initial asymmetry of an
anomalous -charge, and soft leptogenesis reembodies in -genesis.Comment: References updated. Some minor corrections to match the published
versio
Enhancing lepton flavour violation in the supersymmetric inverse seesaw beyond the dipole contribution
In minimal supersymmetric models the -penguin usually provides
sub-dominant contributions to charged lepton flavour violating observables. In
this study, we consider the supersymmetric inverse seesaw in which the
non-minimal particle content allows for dominant contributions of the
-penguin to several lepton flavour violating observables. In particular, and
due to the low-scale (TeV) seesaw, the penguin contribution to, for instance,
\Br(\mu \to 3e) and conversion in nuclei, allows to render some of
these observables within future sensitivity reach. Moreover, we show that in
this framework, the -penguin exhibits the same non-decoupling behaviour
which had previously been identified in flavour violating Higgs decays in the
Minimal Supersymmetric Standard Model.Comment: 29 pages, 9 figures, 4 tables; v2: minor corrections, version to
appear in JHE
Flavoured soft leptogenesis and natural values of the B term
We revisit flavour effects in soft leptogenesis relaxing the assumption of
universality for the soft supersymmetry breaking terms. We find that with
respect to the case in which the heavy sneutrinos decay with equal rates and
equal CP asymmetries for all lepton flavours, hierarchical flavour
configurations can enhance the efficiency by more than two orders of magnitude.
This translates in more than three order of magnitude with respect to the
one-flavour approximation. We verify that lepton flavour equilibration effects
related to off-diagonal soft slepton masses are ineffective for damping these
large enhancements. We show that soft leptogenesis can be successful for
unusual values of the relevant parameters, allowing for and for values of the washout parameter up to .Comment: 23 pages, 5 figures postscript, Minor changes to match the published
version in JHE
Neutrino Masses at LHC: Minimal Lepton Flavour Violation in Type-III See-saw
We study the signatures of minimal lepton flavour violation in a simple
Type-III see - saw model in which the flavour scale is given by the new fermion
triplet mass and it can be naturally light enough to be produced at the LHC. In
this model the flavour structure of the lepton number conserving couplings of
the triplet fermions to the Standard Model leptons can be reconstructed from
the neutrino mass matrix and the smallness of the neutrino mass is associated
with a tiny violation of total lepton number. Characteristic signatures of this
model include suppressed lepton number violation decays of the triplet
fermions, absence of displaced vertices in their decays and predictable lepton
flavour composition of the states produced in their decays. We study the
observability of these signals in the processes pp\rightarrow 3\ell + 2j
+\Sla{E_T} and with or taking into
account the present low energy data on neutrino physics and the corresponding
Standard Model backgrounds. Our results indicate that the new fermionic states
can be observed for masses up to 500 GeV depending on the CP violating Majorana
phase for an integrated luminosity of 30 fb. Moreover, the flavour of
the final state leptons in the above processes can shed light on the neutrino
mass ordering.Comment: 31 pages, 11 Figures, matches published versio
Minimal models with light sterile neutrinos
We study the constraints imposed by neutrino oscillation experiments on the
minimal extensions of the Standard Model (SM) with gauge singlet fermions
("right-handed neutrinos"), that can account for neutrino masses. We consider
the most general coupling to SM fields of the new fields, in particular those
that break lepton number and we do not assume any a priori hierarchy in the
mass parameters. We proceed to analyze these models starting from the lowest
level of complexity, defined by the number of extra fermionic degrees of
freedom. The simplest choice that has enough free parameters in principle (i.e.
two mass differences and two angles) to explain the confirmed solar and
atmospheric oscillations corresponds to . This minimal choice is shown
to be excluded by data. The next-to-minimal choice corresponds to . We
perform a systematic study of the full parameter space in the limit of
degenerate Majorana masses by requiring that at least two neutrino mass
differences correspond to those established by solar and atmospheric
oscillations. We identify several types of spectra that can fit long-baseline
reactor and accelerator neutrino oscillation data, but fail in explaining solar
and/or atmospheric data. The only two solutions that survive are the expected
seesaw and quasi-Dirac regions, for which we set lower and upper bounds
respectively on the Majorana mass scale. Solar data from neutral current
measurements provide essential information to constrain the quasi-Dirac region.
The possibility to accommodate the LSND/MiniBoone and reactor anomalies, and
the implications for neutrinoless double-beta decay and tritium beta decay are
briefly discussed.Comment: 32 pages, 15 figures. Misprints and a small error corrected,
references added. Conclusions unchange
Radiolabelled peptides for oncological diagnosis
Radiolabelled receptor-binding peptides targeting receptors (over)expressed on tumour cells are widely under investigation for tumour diagnosis and therapy. The concept of using radiolabelled receptor-binding peptides to target receptor-expressing tissues in vivo has stimulated a large body of research in nuclear medicine. The 111In-labelled somatostatin analogue octreotide (OctreoScan™) is the most successful radiopeptide for tumour imaging, and was the first to be approved for diagnostic use. Based on the success of these studies, other receptor-targeting peptides such as cholecystokinin/gastrin analogues, glucagon-like peptide-1, bombesin (BN), chemokine receptor CXCR4 targeting peptides, and RGD peptides are currently under development or undergoing clinical trials. In this review, we discuss some of these peptides and their analogues, with regard to their potential for radionuclide imaging of tumours
Retrospective cohort study: Risk of gastrointestinal cancer in a symptomatic cohort after a complete colonoscopy: Role of faecal immunochemical test
BACKGROUND: Faecal immunochemical test (FIT) has been recommended to assess symptomatic patients for colorectal cancer (CRC) detection. Nevertheless, some conditions could theoretically favour blood originating in proximal areas of the gastrointestinal tract passing through the colon unmetabolized. A positive FIT result could be related to other gastrointestinal cancers (GIC).
AIM: To assess the risk of GIC detection and related death in FIT-positive symptomatic patients (threshold 10 µg Hb/g faeces) without CRC.
METHODS: Post hoc cohort analysis performed within two prospective diagnostic test studies evaluating the diagnostic accuracy of different FIT analytical systems for CRC and significant colonic lesion detection. Ambulatory patients with gastrointestinal symptoms referred consecutively for colonoscopy from primary and secondary healthcare, underwent a quantitative FIT before undergoing a complete colonoscopy. Patients without CRC were divided into two groups (positive and negative FIT) using the threshold of 10 µg Hb/g of faeces and data from follow-up were retrieved from electronic medical records of the public hospitals involved in the research. We determined the cumulative risk of GIC, CRC and upper GIC. Hazard rate (HR) was calculated adjusted by age, sex and presence of significant colonic lesion.
RESULTS: We included 2709 patients without CRC and a complete baseline colonoscopy, 730 (26.9%) with FIT = 10 µgr Hb/gr. During a mean time of 45.5 ± 20.0 mo, a GIC was detected in 57 (2.1%) patients: An upper GIC in 35 (1.3%) and a CRC in 14 (0.5%). Thirty-six patients (1.3%) died due to GIC: 22 (0.8%) due to an upper GIC and 9 (0.3%) due to CRC. FIT-positive subjects showed a higher CRC risk (HR 3.8, 95%CI: 1.2-11.9) with no differences in GIC (HR 1.5, 95%CI: 0.8-2.7) or upper GIC risk (HR 1.0, 95%CI: 0.5-2.2). Patients with a positive FIT had only an increased risk of CRC-related death (HR 10.8, 95%CI: 2.1-57.1) and GIC-related death (HR 2.2, 95%CI: 1.1-4.3), with no differences in upper GIC-related death (HR 1.4, 95%CI: 0.6-3.3). An upper GIC was detected in 22 (0.8%) patients during the first year. Two variables were independently associated: anaemia (OR 5.6, 95%CI: 2.2-13.9) and age = 70 years (OR 2.7, 95%CI: 1.1-7.0).
CONCLUSION: Symptomatic patients without CRC have a moderate risk increase in upper GIC, regardless of the FIT result. Patients with a positive FIT have an increased risk of post-colonoscopy CRC