171 research outputs found
The NMSSM lives: with the 750 GeV diphoton excess
We propose an NMSSM scenario that can explain the excess in the diphoton
spectrum at 750 GeV recently observed by ATLAS and CMS. We show that in a
certain limit with a very light pseudoscalar one can reproduce the experimental
results without invoking exotic matter. The 750 GeV excess is produced by two
resonant heavy Higgs bosons with masses ~750 GeV, that subsequently decay to
two light pseudoscalars. Each of these decays to collimated photon pairs that
appear as a single photon in the electromagnetic calorimeter. A mass gap
between heavy Higgses mimics a large width of the 750 GeV peak. The production
mechanism, containing a strong component via initial b quarks, ameliorates a
possible tension with 8 TeV data compared to other production modes. We also
discuss other constraints, in particular from low energy experiments. Finally,
we discuss possible methods that could distinguish our proposal from other
physics models describing the diphoton excess in the Run-II of the LHC.Comment: 24 pages, 4 figures; minor text improvements; to appear in EPJ
A resonance without resonance: scrutinizing the diphoton excess at 750 GeV
Motivated by the recent diphoton excesses reported by both ATLAS and CMS
collaborations, we suggest that a new heavy spinless particle is produced in
gluon fusion at the LHC and decays to a couple of lighter pseudoscalars which
then decay to photons. The new resonances could arise from a new strongly
interacting sector and couple to Standard Model gauge bosons only via the
corresponding Wess-Zumino-Witten anomaly. We present a detailed recast of the
newest 13 TeV data from ATLAS and CMS together with the 8 TeV data to scan the
consistency of the parameter space for those resonances.Comment: 8 pages, 4 figures, extended discussion of underlying models, new
plots with varying mass of the heavy scalar, to appear in PL
CP violation at one loop in the polarization-independent chargino production in e+e- collisions
Recently Osland and Vereshagin noticed, based on sample calculations of some
box diagrams, that in unpolarised e+e- collisions CP-odd effects in the
non-diagonal chargino-pair production process are generated at one-loop. Here
we perform a full one-loop analysis of these effects and point out that in some
cases the neglected vertex and self-energy contributions may play a dominant
role. We also show that CP asymmetries in chargino production are sensitive not
only to the phase of mu parameter in the chargino sector but also to the phase
of stop trilinear coupling A_t.Comment: 14 pages, 5 figure
Reducing the fine-tuning of gauge-mediated SUSY breaking
Despite their appealing features, models with gauge-mediated supersymmetry breaking (GMSB) typically present a high degree of fine-tuning, due to the initial absence of the top trilinear scalar couplings, At = 0. In this paper, we carefully evaluate such a tuning, showing that is worse than per mil in the minimal model. Then, we examine some existing proposals to generate At ≠0 term in this context. We find that, although the stops can be made lighter, usually the tuning does not improve (it may be even worse), with some exceptions, which involve the generation of At at one loop or tree level. We examine both possibilities and propose a conceptually simplified version of the latter; which is arguably the optimum GMSB setup (with minimal matter content), concerning the fine-tuning issue. The resulting fine-tuning is better than one per mil, still severe but similar to other minimal supersymmetric standard model constructions. We also explore the so-called “little A2t /m2 problem”, i.e. the fact that a large At -term is normally accompanied by a similar or larger sfermion mass, which typically implies an increase in the fine-tuning. Finally, we find the version of GMSB for which this ratio is optimized, which, nevertheless, does not minimize the fine-tuningThis work has been partially supported by the MICINN, Spain, under contract FPA2013-44773-P, Consolider-Ingenio CPAN CSD2007-00042, as well as MULTIDARK CSD2009-00064. We also thank the Spanish MINECO Centro de excelencia Severo Ochoa Program under Grant SEV-2012-0249. S.R. is supported by the Campus of Excellence UAM+CSIC and K.R. by the Spanish Research Council (CSIC) within the JAE-Doc progra
LHC/ILC Interplay in SUSY Searches
Combined analyses at the Large Hadron Collider and at the International
Linear Collider are important to reveal precisely the new physics model as, for
instance, supersymmetry. Examples are presented where ILC results as input for
LHC analyses could be crucial for the identification of signals as well as of
the underlying model. The synergy of both colliders leads also to rather
accurate SUSY parameter determination and powerful mass constraints even if the
scalar particles have masses in the multi-TeV range.Comment: 5 pages, contribution to the proceedings of EPS0
Normal tau polarisation as a sensitive probe of CP violation in chargino decay
CP violation in the spin-spin correlations in chargino production and
subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC.
From the normal polarisation of the tau, an asymmetry is defined to test the
CP-violating phase of the higgsino mass parameter \mu. Asymmetries of more than
\pm70% are obtained, also in scenarios with heavy first and second generation
sfermions. Bounds on the statistical significances of the CP asymmetries are
estimated. As a result, the normal tau polarisation in the chargino decay is
one of the most sensitive probes to constrain or measure the phase \phi_\mu at
the ILC, motivating further detailed experimental studies.Comment: 20 pages, 10 figures, gzipped tar fil
How low can SUSY go? Matching, monojets and compressed spectra
If supersymmetry (SUSY) has a compressed spectrum then the current mass
limits from the LHC can be drastically reduced. We consider a possible 'worst
case' scenario where the gluino and/or squarks are degenerate with the lightest
SUSY particle (LSP). The most sensitive searches for these compressed spectra
are via the final state LSPs recoiling against initial state radiation (ISR).
Therefore it is vital that the ISR is understood and possible uncertainties in
the predictions are evaluated. We use both MLM (with Pythia 6) and CKKW- L
(with Pythia 8) matching and vary matching scales and parton shower properties
to accurately determine the theoretical uncertainties in the kinematic
distributions. All current LHC SUSY and monojet analyses are employed and we
find the most constraining limits come from the CMS Razor and CMS monojet
searches. For a scenario of squarks degenerate with the LSP and decoupled
gluinos we find GeV. For gluinos degenerate with the LSP
and decoupled squarks, GeV. For equal mass squarks and
gluinos degenerate with the LSP, GeV.Comment: References added, version submitted to ep
Constraining compressed supersymmetry using leptonic signatures
We study the impact of the multi-lepton searches at the LHC on supersymmetric
models with compressed mass spectra. For such models the acceptances of the
usual search strategies are significantly reduced due to requirement of large
effective mass and missing E_T. On the other hand, lepton searches do have much
lower thresholds for missing E_T and p_T of the final state objects. Therefore,
if a model with a compressed mass spectrum allows for multi-lepton final
states, one could derive constraints using multi-lepton searches. For a class
of simplified models we study the exclusion limits using ATLAS multi-lepton
search analyses for the final states containing 2-4 electrons or muons with a
total integrated luminosity of 1-2/fb at \sqrt{s}=7 TeV. We also modify those
analyses by imposing additional cuts, so that their sensitivity to compressed
supersymmetric models increase. Using the original and modified analyses, we
show that the exclusion limits can be competitive with jet plus missing E_T
searches, providing exclusion limits up to gluino masses of 1 TeV. We also
analyse the efficiencies for several classes of events coming from different
intermediate state particles. This allows us to assess exclusion limits in
similar class of models with different cross sections and branching ratios
without requiring a Monte Carlo simulation.Comment: 18 pages, 5 figure
Combined LHC/ILC analysis of a SUSY scenario with heavy sfermions
We discuss the potential of combined analyses at the Large Hadron Collider
and the planned International Linear Collider to explore low-energy
supersymmetry in a difficult region of the parameter space characterized by
masses of the scalar SUSY particles around 2 TeV. Precision analyses of cross
sections for light chargino production and forward--backward asymmetries of
decay leptons and hadrons at the ILC, together with mass information on chi^0_2
and squarks from the LHC, allow us to determine the underlying fundamental
gaugino/higgsino MSSM parameters and to constrain the masses of the heavy,
kinematically inaccessible sparticles. No assumptions on a specific
SUSY-breaking mechanism are imposed. For this analysis the complete spin
correlations between production and decay processes are taken into account.Comment: new figure added, updated to match the published versio
Physics at the e+ e- Linear Collider
A comprehensive review of physics at an e+e- Linear Collider in the energy
range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC
results, experiments from low energy as well as astroparticle physics.The
report focuses in particular on Higgs boson, Top quark and electroweak
precision physics, but also discusses several models of beyond the Standard
Model physics such as Supersymmetry, little Higgs models and extra gauge
bosons. The connection to cosmology has been analyzed as well.Comment: 179 pages, plots and references updated, version to be published at
EPJ
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