87 research outputs found
Sensitivities of Prospective Future e+e- Colliders to Decoupled New Physics
We explore the indirect sensitivities to decoupled new physics of prospective
precision electroweak measurements, triple-gauge-coupling measurements and
Higgs physics at future colliders, with emphasis on the ILC250 and
FCC-ee. The Standard Model effective field theory (SM EFT) is adopted as a
model-independent approach for relating experimental precision projections to
the scale of new physics, and we present prospective constraints on the Wilson
coefficients of dimension-6 operators. We find that in a marginalised fit
ILC250 EWPT measurements may be sensitive to new physics scales ~TeV, and FCC-ee EWPT measurements may be sensitive to ~TeV. The prospective sensitivities of Higgs and TGC
measurements at the ILC250 (FCC-ee) are to ~TeV
(~TeV).Comment: 19 page
Associated Production Evidence against Higgs Impostors and Anomalous Couplings
There is still no proof that the new particle recently discovered by the
ATLAS and CMS Collaborations indeed has spin zero and positive parity, as
confidently expected. We show here that the energy dependence of associated
production would be much less for a boson with minimal
couplings, such as the Higgs boson of the Standard Model, than for a spin-two
particle with graviton-like couplings or a spin-zero boson with non-minimal
couplings. The signal apparently observed by the CDF
and D0 Collaborations can be used to predict the cross section for the same
signal at the LHC that should be measured under the spin-two and different
spin-zero hypotheses. The spin-two prediction exceeds by an order of magnitude
the upper limits established by the ATLAS and CMS Collaborations, which are
consistent with the minimal prediction, thereby providing {\it secunda
facie} evidence against spin-two Higgs impostors. Similar analyses of energy
dependences provide evidence against impostors, non-minimal scalar boson
couplings, including the best LHC limits on dimension-six operators. Comparing
the LHC vector boson fusion cross sections at 7 and 8 TeV in the centre of mass
provides additional but weaker evidence in favour of the identification of the
particle as a boson with minimal couplings.Comment: 15 pages, 7 figure
Prima Facie Evidence against Spin-Two Higgs Impostors
The new particle X recently discovered by the ATLAS and CMS Collaborations is
widely expected to have spin zero, but this remains to be determined. The
leading alternative is that X has spin two, presumably with graviton-like
couplings. We show that measurements of the X particle to pairs of vector
bosons constrain such scenarios. In particular, a graviton-like Higgs impostor
in scenarios with a warped extra dimension of AdS type is prima facie excluded,
principally because they predict too small a ratio between the X couplings to
WW and ZZ, compared with that to photons. The data also disfavour universal
couplings to pairs of photons and gluons, which would be predicted in a large
class of graviton-like models.Comment: 17 pages, 3 figure
The Price of an Electroweak Monopole
In a recent paper, Cho, Kim and Yoon (CKY) have proposed a version of the
SU(2) U(1) Standard Model with finite-energy monopole and dyon
solutions. The CKY model postulates that the effective U(1) gauge coupling very rapidly as the Englert-Brout-Higgs vacuum expectation value , but in a way that is incompatible with LHC measurements of the Higgs boson
decay rate. We construct generalizations of the CKY model
that are compatible with the constraint, and calculate
the corresponding values of the monopole and dyon masses. We find that the
monopole mass could be TeV, so that it could be pair-produced at the
LHC and accessible to the MoEDAL experiment.Comment: 15 pages; Two clarifying footnotes (3 and 4) added. No effect on
conclusion
The Case for Future Hadron Colliders From Decays
Recent measurements in decays are somewhat
discrepant with Standard Model predictions. They may be harbingers of new
physics at an energy scale potentially accessible to direct discovery. We
estimate the sensitivity of future hadron colliders to the possible new
particles that may be responsible for the anomalies: leptoquarks or
s. We consider luminosity upgrades for a 14 TeV LHC, a 33 TeV LHC,
and a 100 TeV collider such as the FCC-hh. Coverage of models
is excellent: for narrow particles, with perturbative couplings that may
explain the -decay results for masses up to 20 TeV, a 33 TeV 1
ab LHC is expected to cover most of the parameter space up to 8 TeV in
mass, whereas the 100 TeV FCC-hh with 10 ab will cover all of it. A
smaller portion of the leptoquark parameter space is covered by future
colliders: for example, in a di-leptoquark search, a 100 TeV 10
ab collider has a projected sensitivity up to leptoquark masses of 12
TeV (extendable to 21 TeV with a strong coupling for single leptoquark
production), whereas leptoquark masses up to 41 TeV may in principle explain
the anomalies.Comment: 24 pages, 10 figures. v2: Improved discussion and references added,
version submitted to JHE
Light-by-Light Scattering Constraint on Born-Infeld Theory
The recent measurement by ATLAS of light-by-light scattering in LHC Pb-Pb
collisions is the first direct evidence for this basic process. We find that it
requires the mass scale of a nonlinear Born-Infeld extension of QED to be
~GeV, a much stronger constraint than those derived previously. In
the case of a Born-Infeld extension of the Standard Model in which the
U(1) hypercharge gauge symmetry is realized nonlinearly, the limit on
the corresponding mass scale is ~GeV, which in turn imposes a lower
limit of ~TeV on the magnetic monopole mass in such a U(1) Born-Infeld theory.Comment: 11 pages, 4 figures, version accepted for publication in PR
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