42 research outputs found
Inference Based on Conditional Moment Inequalities
In this paper, we propose an instrumental variable approach to constructing confidence sets (CS's) for the true parameter in models defined by conditional moment inequalities/equalities. We show that by properly choosing instrument functions, one can transform conditional moment inequalities/equalities into unconditional ones without losing identification power. Based on the unconditional moment inequalities/equalities, we construct CS's by inverting Cramer-von Mises-type or Kolmogorov-Smirnov-type tests. Critical values are obtained using generalized moment selection (GMS) procedures. We show that the proposed CS's have correct uniform asymptotic coverage probabilities. New methods are required to establish these results because an infinite-dimensional nuisance parameter affects the asymptotic distributions. We show that the tests considered are consistent against all fixed alternatives and have power against n^{-1/2}-local alternatives to some, but not all, sequences of distributions in the null hypothesis. Monte Carlo simulations for four different models show that the methods perform well in finite samples.Asymptotic size, Asymptotic power, Conditional moment inequalities, Confidence set, Cramer-von Mises, Generalized moment selection, Kolmogorov-Smirnov, Moment inequalities
Minimal lepton flavor violating realizations of minimal seesaw models
We study the implications of the global U(1)R symmetry present in minimal
lepton flavor violating implementations of the seesaw mechanism for neutrino
masses. In the context of minimal type I seesaw scenarios with a slightly
broken U(1)R, we show that, depending on the R-charge assignments, two classes
of generic models can be identified. Models where the right-handed neutrino
masses and the lepton number breaking scale are decoupled, and models where the
parameters that slightly break the U(1)R induce a suppression in the light
neutrino mass matrix. We show that within the first class of models,
contributions of right-handed neutrinos to charged lepton flavor violating
processes are severely suppressed. Within the second class of models we study
the charged lepton flavor violating phenomenology in detail, focusing on mu to
e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable
contributions to these processes are naturally obtained for right-handed
neutrino masses at the TeV scale. We then discuss the interplay with the
effects of the right-handed neutrino interactions on primordial B - L
asymmetries, finding that sizable right-handed neutrino contributions to
charged lepton flavor violating processes are incompatible with the requirement
of generating (or even preserving preexisting) B - L asymmetries consistent
with the observed baryon asymmetry of the Universe.Comment: 21 pages, 4 figures; version 2: Discussion on possible generic models
extended, typos corrected, references added. Version matches publication in
JHE
Muon conversion to electron in nuclei in type-I seesaw models
We compute the muon to electron conversion in the type-I seesaw model, as a
function of the right-handed neutrino mixings and masses. The results are
compared with previous computations in the literature. We determine the
definite predictions resulting for the ratios between the muon to electron
conversion rate for a given nucleus and the rate of two other processes which
also involve a mu-e flavour transition: mu -> e gamma and mu -> eee. For a
quasi-degenerate mass spectrum of right-handed neutrino masses -which is the
most natural scenario leading to observable rates- those ratios depend only on
the seesaw mass scale, offering a quite interesting testing ground. In the case
of sterile neutrinos heavier than the electroweak scale, these ratios vanish
typically for a mass scale of order a few TeV. Furthermore, the analysis
performed here is also valid down to very light masses. It turns out that
planned mu -> e conversion experiments would be sensitive to masses as low as 2
MeV. Taking into account other experimental constraints, we show that future mu
-> e conversion experiments will be fully relevant to detect or constrain
sterile neutrino scenarios in the 2 GeV-1000 TeV mass range.Comment: 32 pages 14 figures, references added and some minor precisions;
results unchange
Loop corrections to dark matter direct detection in a pseudoscalar mediator dark matter model
If dark matter (DM) is a fermion and its interactions with the standard model
particles are mediated by pseudoscalar particles, the tree-level amplitude for
the DM-nucleon elastic scattering is suppressed by the momentum transfer in the
non-relativistic limit. At the loop level, on the other hand, the
spin-independent contribution to the cross section appears without such
suppression. Thus, the loop corrections are essential to discuss the
sensitivities of the direct detection experiments for the model prediction. The
one-loop corrections were investigated in the previous works. However, the
two-loop diagrams give the leading order contribution to the DM-gluon effective
operator () and have not been
correctly evaluated yet. Moreover, some interaction terms which affect the
scattering cross section were overlooked. In this paper, we show the cross
section obtained by the improved analysis and discuss the region where the
cross section becomes large.Comment: 34 pages, 11 figures, 6 tables, the version published in JHE
Direct Detection of Electroweak Dark Matter
TeV-scale dark matter is well motivated by notions of naturalness as the new
physics threshold is expected to emerge in the TeV regime. We extend the
Standard Model by adding an arbitrary SU(2) dark matter multiplet in non-chiral
representation. The pseudo-real representations can be viable DM candidates
providing that one includes a higher dimensional mass-splitting operator, which
avoids the tree-level inelastic scattering through Z-boson exchange. These
effective operators give rise to sizable contributions from Higgs mediated dark
matter interactions with quarks and gluons. A linear combination of the
effective couplings named is identified as the critical parameter in
determining the magnitude of the cross-section. When is smaller than
the critical value, the theory behaves similar to the known renormalisable
model, and the scattering rate stays below the current experimental reach.
Nevertheless, above the criticality, the contribution from the higher
dimensional operators significantly changes the phenomenology. The scattering
amplitude of pseudo-real models will be coherently enhanced, so that it would
be possible for next generation large-exposure experiments to fully probe these
multiplets. We studied the parameter space of the theory, taking into account
both indirect astrophysical and direct search constraints. It is inferred that
multi-TeV mass scale remains a viable region, quite promising for forthcoming
dark matter experiments
Graph-based learning under perturbations via total least-squares
Graphs are pervasive in different fields unveiling complex relationships between data. Two major graph-based learning tasks are topology identification and inference of signals over graphs. Among the possible models to explain data interdependencies, structural equation models (SEMs) accommodate a gamut of applications involving topology identification. Obtaining conventional SEMs though requires measurements across nodes. On the other hand, typical signal inference approaches “blindly trust” a given nominal topology. In practice however, signal or topology perturbations may be present in both tasks, due to model mismatch, outliers, outages or adversarial behavior. To cope with such perturbations, this work introduces a regularized total least-squares (TLS) approach and iterative algorithms with convergence guarantees to solve both tasks. Further generalizations are also considered relying on structured and/or weighted TLS when extra prior information on the perturbation is available. Analyses with simulated and real data corroborate the effectiveness of the novel TLS-based approaches