378 research outputs found
Heavy Higgs Searches: Flavour Matters
We point out that the stringent lower bounds on the masses of additional
electrically neutral and charged Higgs bosons crucially depend on the flavour
structure of their Yukawa interactions. We show that these bounds can easily be
evaded by the introduction of flavour-changing neutral currents in the Higgs
sector. As an illustration, we study the phenomenology of a two Higgs doublet
model with a Yukawa texture singling out the third family of quarks and
leptons. We combine constraints from low-energy flavour physics measurements,
LHC measurements of the 125 GeV Higgs boson rates, and LHC searches for new
heavy Higgs bosons. We propose novel LHC searches that could be performed in
the coming years to unravel the existence of these new Higgs bosons.Comment: 41 pages, 11 figures and 4 tables (v2: References added. Comment on
associated production with a top quark added. Matched published version.
Illuminating Dark Photons with High-Energy Colliders
High-energy colliders offer a unique sensitivity to dark photons, the
mediators of a broken dark U(1) gauge theory that kinetically mixes with the
Standard Model (SM) hypercharge. Dark photons can be detected in the exotic
decay of the 125 GeV Higgs boson, h -> Z Z_D -> 4l, and in Drell-Yan events, pp
-> Z_D -> ll. If the dark U(1) is broken by a hidden-sector Higgs mechanism,
then mixing between the dark and SM Higgs bosons also allows the exotic decay h
-> Z_D Z_D -> 4l. We show that the 14 TeV LHC and a 100 TeV proton-proton
collider provide powerful probes of both exotic Higgs decay channels. In the
case of kinetic mixing alone, direct Drell-Yan production offers the best
sensitivity to Z_D, and can probe epsilon >~ 9 x 10^(-4) (4 x 10^(-4)) at the
HL-LHC (100 TeV pp collider). The exotic Higgs decay h -> Z Z_D offers slightly
weaker sensitivity, but both measurements are necessary to distinguish the
kinetically mixed dark photon from other scenarios. If Higgs mixing is also
present, then the decay h -> Z_D Z_D can allow sensitivity to the Z_D for
epsilon >~ 10^(-9) - 10^(-6) (10^(-10) - 10^(-7)) for the mass range 2 m_mu <
m_(Z_D) < m_h/2 by searching for displaced dark photon decays. We also compare
the Z_D sensitivity at pp colliders to the indirect, but model-independent,
sensitivity of global fits to electroweak precision observables. We perform a
global electroweak fit of the dark photon model, substantially updating
previous work in the literature. Electroweak precision measurements at LEP,
Tevatron, and the LHC exclude epsilon as low as 3 x 10^(-2). Sensitivity can be
improved by up to a factor of ~2 with HL-LHC data, and an additional factor of
~4 with ILC/GigaZ data.Comment: 36 pages + references, 14 figures, 3 tables. Fixed typos, added
reference
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