119 research outputs found
Interference effects of neutral MSSM Higgs bosons with a generalised narrow-width approximation
Mixing effects in the MSSM Higgs sector can give rise to a sizeable
interference between the neutral Higgs bosons. On the other hand, factorising a
more complicated process into production and decay parts by means of the
narrow-width approximation (NWA) simplifies the calculation. The standard NWA,
however, does not account for interference terms. Therefore, we introduce a
generalisation of the NWA (gNWA) which allows for a consistent treatment of
interference effects between nearly mass-degenerate particles. Furthermore, we
apply the gNWA at the tree and 1-loop level to an example process where the
neutral Higgs bosons and are produced in the decay of a heavy
neutralino and subsequently decay into a fermion pair. The propagator
mixing is found to agree well with the approximation of Breit-Wigner
propagators times finite wave-function normalisation factors, both leading to a
significant interference contribution. The factorisation of the interference
term based on on-shell matrix elements reproduces the full interference result
within a precision of better than 1% for the considered process. The gNWA also
enables the inclusion of contributions beyond the 1-loop order into the most
precise prediction.Comment: 7 pages, 7 figures, Contribution to the proceedings of ICHEP 201
Impact of CP-violating interference effects on MSSM Higgs searches
Interference and mixing effects between neutral Higgs bosons in the MSSM with
complex parameters are shown to have a significant impact on the interpretation
of LHC searches for additional Higgs bosons. Complex MSSM parameters introduce
mixing between the CP-even and CP-odd Higgs states and generate CP-violating
interference terms. Both effects are enhanced in the case of almost degenerate
states. Employing as an example an extension of a frequently used benchmark
scenario by a non-zero phase , the interference contributions are
obtained for the production of neutral Higgs bosons in gluon-fusion and in
association with b-quarks followed by the decay into a pair of -leptons.
While the resonant mixing increases the individual cross sections for the two
heavy Higgs bosons and , strongly destructive interference effects
between the contributions involving and leave a considerable
parameter region unexcluded that would appear to be ruled out if the
interference effects were neglected.Comment: 30 pages, 7 figure
Interference effects in MSSM Higgs searches at the LHC
Complex parameters in the MSSM lead to mixing and interference between the
two heavier neutral CP-even and CP-odd Higgs states. These effects can become
very large in the case of almost degenerate states. In a CP-violating benchmark
scenario, we investigate phenomenological implications of such interferences in
view of the LHC searches for heavy Higgs bosons decaying to a pair of
-leptons and produced in gluon fusion and in association with b-quarks.
Strongly destructive effects leave parameter regions unconstrained that would
be regarded as excluded if no interference terms were taken into account.Comment: 5 pages, 2 figures; conference C16-08-03; references updated, some
clarification
Interference effects of neutral MSSM Higgs bosons with a generalised narrow-width approximation
AbstractMixing effects in the MSSM Higgs sector can give rise to a sizeable interference between the neutral Higgs bosons. On the other hand, factorising a more complicated process into production and decay parts by means of the narrow-width approximation (NWA) simplifies the calculation. The standard NWA, however, does not account for interference terms. Therefore, we introduce a generalisation of the NWA (gNWA) which allows for a consistent treatment of interference effects between nearly mass-degenerate particles. Furthermore, we apply the gNWA at the tree and 1-loop level to an example process where the neutral Higgs bosons h and H are produced in the decay of a heavy neutralino and subsequently decay into a fermion pair. The h – H propagator mixing is found to agree well with the approximation of Breit-Wigner propagators times finite wave-function normalisation factors, both leading to a significant interference contribution. The factorisation of the interference term based on on-shell matrix elements reproduces the full interference result within a precision of better than 1% for the considered process. The gNWA also enables the inclusion of contributions beyond the 1-loop order into the most precise prediction
Relaxion and light (pseudo)scalars at the HL-LHC and lepton colliders
We study the potential of future lepton colliders, running at the Z-pole and
above, and the High-Luminosity LHC to search for the relaxion and other light
scalars . We investigate the interplay of direct searches and precision
observables for both CP-even and -odd couplings. In particular, precision
measurements of exotic Z-decays, Higgs couplings, the exotic Higgs decay into a
relaxion pair and associated and production are promising
channels to yield strong bounds.Comment: 27 pages + references, 5 figures, 2 table
-violating effects on MSSM Higgs searches
We study the effects of -violating phases on the phenomenology
of the Higgs sector of the MSSM. Complex parameters in the MSSM lead to
-violating mixing between the tree-level -even and
-odd neutral Higgs states, leading to three new loop-corrected
mass eigenstates , . For scenarios where a
light Higgs boson at about 125 GeV can be identified with the observed signal
and where the other Higgs states are significantly heavier, a large admixture
of the heavy neutral Higgs bosons occurs as a generic feature if
-violating effects are taken into account. Including interference
contributions in the predictions for cross sections times branching ratios of
the Higgs bosons is essential in this case. As a first step, we present the
gluon-fusion and bottom-quark annihilation cross sections for for the
general case of arbitrary complex parameters, and we demonstrate that squark
effects strongly depend on the phases of the complex parameters. We then study
the effects of interference between and for the example of the
process . We show that large destructive
interference effects modify LHC exclusion bounds such that parts of the
parameter space that would be excluded by MSSM Higgs searches under the
assumption of -conservation open up when the possibility of
-violation in the Higgs sector is accounted for.Comment: 11 pages, 4 figures, contribution to the HiggsTools Final Meeting,
Durha
Phenomenology of relaxion-Higgs mixing
We show that the relaxion generically stops its rolling at a point that
breaks CP leading to relaxion-Higgs mixing. This opens the door to a variety of
observational probes since the possible relaxion mass spans a broad range from
sub-eV to the GeV scale. We derive constraints from current experiments (fifth
force, astrophysical and cosmological probes, beam dump, flavour, LEP and LHC)
and present projections from future experiments such as NA62, SHiP and PIXIE.
We find that a large region of the parameter space is already under the
experimental scrutiny. All the experimental constraints we derive are equally
applicable for general Higgs portal models. In addition, we show that simple
multiaxion (clockwork) UV completions suffer from a mild fine tuning problem,
which increases with the number of sites. These results favour a cut-off scale
lower than the existing theoretical bounds.Comment: 46 pages, 6 figures, v3: typos fixed, references added, version
matches the version published in JHE
Interference effects in BSM processes with a generalised narrow-width approximation
A generalisation of the narrow-width approximation (NWA) is formulated which
allows for a consistent treatment of interference effects between nearly
mass-degenerate particles in the factorisation of a more complicated process
into production and decay parts. It is demonstrated that interference effects
of this kind arising in BSM models can be very large, leading to drastic
modifications of predictions based on the standard NWA. The application of the
generalised NWA is demonstrated both at tree level and at one-loop order for an
example process where the neutral Higgs bosons and of the MSSM are
produced in the decay of a heavy neutralino and subsequently decay into a
fermion pair. The generalised NWA, based on on-shell matrix elements or their
approximations leading to simple weight factors, is shown to produce UV- and
IR-finite results which are numerically close to the result of the full process
at tree level and at one-loop order, where an agreement of better than is
found for the considered process. The most accurate prediction for this process
based on the generalised NWA, taking into account also corrections that are
formally of higher orders, is briefly discussed.Comment: 44 pages, 17 figure
- …