37 research outputs found
Lurking pseudovectors below the TeV scale
If electroweak symmetry breaking is driven by a new strongly-coupled
dynamical sector, one expects their bound states to appear at the TeV scale or
slightly below. However, electroweak precision data imposes severe constraints
on most of the existing models, putting them under strain. Conventional models
require the new composite states to come in pairs of rather heavy, close to
degenerate spin-1 resonances. In this paper I argue that spin-1 states can
actually be lighter without clashing with experimental bounds. As an example, I
consider a composite model with a light pseudovector resonance that couples to
the Standard Model gauge boson, fermion and scalar fields. I show how such a
resonance leaves basically no imprint on the NLO corrections to the Standard
Model. This happens not through parameter tuning, but rather as a consequence
of generic properties of realistic UV completions. This pseudovector is mostly
unconstrained by existing data and could be as light as 600 GeV. In the last
part of the paper I briefly discuss its most characteristic signatures for
direct detection at colliders.Comment: 8 pages, 2 figure
Standard Model prediction and new physics tests for D0 -> h+h-l+l- (h=\pi,K; l=e,\mu)
Motivated by the recent evidence for direct CP-violation in D0 -> h+h-
decays, we provide an exhaustive study of both Cabibbo-favored and
Cabibbo-suppressed (singly and doubly) D0 -> h1+h2-l+l- decays. In particular,
we study the Dalitz plot for the long-distance contributions in the
(m_{ll}^2,m_{hh}^2) parameter space. We find that near-resonant effects, i.e.,
D0 -> V(h1+h2-)l+l- with V=\rho,K*,\phi, are sizeable and even dominant (over
Bremsstrahlung) for the \mu+\mu- decay modes, bringing the branching ratios
close to the LHCb reach. We also provide a detailed study of the angular
asymmetries for such decays and identify signatures for new physics detection.
In particular, new physics signals can be neatly isolated in asymmetries
involving the semileptonic operator Q_{10}, where for typical new physics
scenarios the effects can be as sizeable as O(1%) for the doubly
Cabibbo-suppressed modes.Comment: 19 pages, 5 figures. v2 (journal version) contains the new subsection
III.B, where the potential size of new physics effects is discussed. Tables
and figures slightly changed to match the journal version. Typos corrected
and references added. Conclusions unchange