1,720,981 research outputs found
Charged lepton flavour violation: An experimental and theoretical introduction
No full textCharged lepton flavour-violating transitions would be a clear signal of new physics beyond the Standard Model. Their search has been carried out in a variety of channels, the most sensitive being those involving a muon: However no positive evidence has been found so far. The MEG experiment has recently set the best limit on such processes by investigating the existence of the μ → eγ decay. In the next decade several experiments are planned to pursue the search for μ → eγ, μ → eee, μ → e conversion in nuclei, as well as on processes involving the t, to an unprecedented level of precision. In this review we want to give a pedagogical introduction on the theoretical motivations for such searches as well as on the experimental aspects upon which they are based
Phenomenology of SUSY SU(5) with type I+III seesaw
No full textWe consider a supersymmetric SU(5) model where two neutrino masses are obtained via a mixed type I+III seesaw mechanism induced by the component fields of a single SU(5) adjoint. We have analyzed the phenomenology of the model paying particular attention to flavour violating processes and dark matter relic density. We have found that, for a seesaw scale larger than ~GeV, Br is in the reach of the MEG experiment in sizable regions of the parameter space. On the other side, current bounds on it force Br to be well below the reach of forthcoming experiments, rendering thus the model disprovable if a positive signal is found. The same bounds still allow for a sizable positive contribution to , while the CP violation in the mixing turns out to be too small to account for the di-muon anomaly reported by the D0 collaboration. Finally, the regions where the neutralino relic density is within the WMAP bounds can be strongly modified with respect to the constrained MSSM case. In particular, a peculiar coannihilation region, bounded from above, can be realized, which allows us to put an upper bound on the dark matter mass for certain set-ups of the parameters
Gauge coupling unification, the GUT scale, and magic fields
No full textAbstractWe consider field sets that do not form complete SU(5) multiplets, but exactly preserve the one-loop MSSM prediction for α3(MZ) independently of the value of their mass. Such fields can raise the unification scale in different ways, through a delayed convergence of the gauge couplings, a fake unified running below the GUT scale, or a postponed unification after a hoax crossing at a lower scale. The α3(MZ) prediction is independent of the mass of the new fields, while the GUT scale often is not, which allows to vary the GUT scale. Such “magic” fields represent a useful tool in GUT model building. For example, they can be used to fix gauge coupling unification in certain two step breakings of the unified group, to suppress large KK thresholds in models with extra dimensions, or they can be interpreted as messengers of supersymmetry breaking in GMSB models
Consequences of a unified, anarchical model of fermion masses and mixings
Full text linkWe show that most features of the mass and mixing pattern of the second and third SM fermion families can be accounted for without making use of flavour symmetries or other types of flavour dynamics. We discuss the implications for flavour phenomenology, in particular for the tau -> mu gamma decay rate, and comment on LFV effects at colliders. We show that the model can be embedded in a full SO(10) supersymmetric GUT in 5 dimensions that preserves the successful MSSM gauge coupling unification prediction for alpha(s). Interesting features of this embedding are i) the connection of one of the hierarchy parameters with the strong coupling assumption, ii) the absence of KK threshold effects on the alpha(s) prediction at one loop, and iii) the shift of the GUT scale up to about 10(17) GeV. Proton decay is under control, also due to the larger GUT scale. A large atmospheric angle for normal hierarchical neutrinos is obtained in an unusual way
Running U(e3) and BR(mu ---> e + gamma) in SUSY-GUTs
No full textIn supersymmetric seesaw models based on SUSY-GUTs, it could happen that the neutrino PMNS mixing
angles are related to the lepton flavour violating decay rates. In particular SO(10) frameworks, the smallest
mixing angle would get directly correlated with the μ → e+
decay amplitude. Here we study this correlation
in detail considering Ue3 as a free parameter between 0 and Ue3(CHOOZ). Large radiative corrections to Ue3
present in these models, typically of the order Ue3 ∼ 10−3 (peculiar to hierarchial neutrinos), can play
a major role in enhancing the Br(μ → e +
), especially when Ue3
<
10−3. For large tan, even such small
enhancements are sufficient to bring the associated Br(μ → e+
) into realm of MEG experiment as long as
SUSY spectrum lies within the range probed by LHC. On the other hand, for some (negative) values of Ue3,
suppressions can occur in the branching ratio, due to cancellations among different contributions. From a
top-down perspective such low values of Ue3 at the weak scale might require some partial/full cancellations
between the high scale parameters of the model and the radiative corrections unless Ue3 is purely of radiative
origin at the high scale. We further emphasize that in Grand Unified theories there exist additional LFV
effects related to the running above the GUT scale, that are also independent on the low energy value of
Ue3. These new contributions can become competitive and even dominant in some regions of the parameter
space
Lepton flavour violation from SUSY-GUTs: Where do we stand for MEG, PRISM/PRIME and a super flavour factory.
No full textWe analyse the complementarity between Lepton Flavour Violation (LFV) and LHC experiments
in probing the Supersymmetric (SUSY) Grand Unified Theories (GUT) when neutrinos got a mass
via the see–saw mechanism. Our analysis is performed in an SO(10) framework, where at least one
neutrino Yukawa coupling is necessarily as large as the top Yukawa coupling. Our study thoroughly
takes into account the whole RG running, including the GUT and the right handed neutrino mass
scales, as well as the running of the observable neutrino spectrum. We find that the upcoming
(MEG, SuperKEKB) and future (PRISM/PRIME, Super Flavour factory) LFV experiments will be
able to test such SUSY framework for SUSY masses to be explored at the LHC and, in some cases,
even beyond the LHC sensitivity reach
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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