5,337 research outputs found
Explanation of the ATLAS Z-peaked excess by squark pair production in the NMSSM
The ATLAS collaboration recently reported a excess in the
leptonic- channel. We intend to interpret this excess by
squark pair production in the Next-to-Minimal Supersymmetric Standard Model
(NMSSM). The decay chain we employ is , where and denote the
lightest and the next-to-lightest neutralinos with singlino and bino as their
dominant components respectively. Our simulations indicate that after
considering the constraints from the ATLAS searches for
signal the central value of the excess can be obtained for , and if the constraint from the CMS on- search is
further considered, more than 10 signal events are still attainable for
. Compared with the interpretation by
gluino pair production, the squark explanation allows for a significantly wider
range of as well as a less compressed SUSY mass spectrum. We
also show that the squark explanation will be readily tested at the initial
stage of the 14 TeV LHC.Comment: 19 pages, 4 figure
Twist-3 contribution to the pion electromagnetic form factor
Non-leading contribution to the pion electromagnetic form factor which comes
from the pion twist-3 wave function is analyzed in the modified hard scattering
approach (MHSA) proposed by Li and Sterman. This contribution is enhanced
significantly due to bound state effect (the twist-3 wave function is
independent of the fractional momentum carried by the parton and has a large
factor with being the pion meson mass and
being the mean u- and d-quark masses). Consequently, although it is suppressed
by the factor , the twist-3 contribution is comparable with and even
larger than the leading twist (twist-2) contribution at intermediate energy
region of being .Comment: 10 pages, 2 fgures, latex. More discussions on the Sudakov effect
added, references added. To appear in European Physical Journal C
(Zeitschrift fur Physik C
Explanation of the ATLAS Z-peaked excess in the NMSSM
Recently the ATLAS collaboration reported a excess in the
leptonic- channel. This may be interpreted in the
Next-to-Minimal Supersymmetric Standard Model (NMSSM) by gluino pair production
with the decay chain , where and denote the
lightest and the next-to-lightest neutralinos with singlino and bino as their
dominant components respectively. After exploring the relevant parameter space
of the NMSSM by considering the constraints from the ATLAS searches for signals, we conclude that the NMSSM is able to explain the excess
at level with the number of the signal events reaching its measured
central value in optimal cases, and the best explanation comes from a
compressed spectrum such as ,
and . We also check the consistency of the ATLAS results with the
null result of the CMS on- search. We find that under the CMS limits at
C.L., the event number of the ATLAS on- signal can still reach 11 in
our scenario, which is about away from the measured central value.Comment: 18 pages, 2 figure
Sneutrino DM in the NMSSM with inverse seesaw mechanism
In supersymmetric theories like the Next-to-Minimal Supersymmetric Standard
Model (NMSSM), the lightest neutralino with bino or singlino as its dominant
component is customarily taken as dark matter (DM) candidate. Since light
Higgsinos favored by naturalness can strength the couplings of the DM and thus
enhance the DM-nucleon scattering rate, the tension between naturalness and DM
direct detection results becomes more and more acute with the improved
experimental sensitivity. In this work, we extend the NMSSM by inverse seesaw
mechanism to generate neutrino mass, and show that in certain parameter space
the lightest sneutrino may act as a viable DM candidate, i.e. it can annihilate
by multi-channels to get correct relic density and meanwhile satisfy all
experimental constraints. The most striking feature of the extension is that
the DM-nucleon scattering rate can be naturally below its current experimental
bounds regardless of the higgsino mass, and hence it alleviates the tension
between naturalness and DM experiments. Other interesting features include that
the Higgs phenomenology becomes much richer than that of the original NMSSM due
to the relaxed constraints from DM physics and also due to the presence of
extra neutrinos, and that the signatures of sparticles at colliders are quite
different from those with neutralino as DM candidate.Comment: 33 page
Interpreting The 750 GeV Diphoton Excess Within Topflavor Seesaw Model
We propose to interpret the 750 GeV diphoton excess in a typical topflavor
seesaw model. The new resonance X can be identified as a CP-even scalar
emerging from a certain bi-doublet Higgs field. Such a scalar can couple to
charged scalars, fermions as well as heavy gauge bosons predicted by the model,
and consequently all of the particles contribute to the diphoton decay mode of
the X. Numerical analysis indicates that the model can predict the central
value of the diphoton excess without contradicting any constraints from 8 TeV
LHC, and among the constraints, the tightest one comes from the Z \gamma
channel, \sigma_{8 {\rm TeV}}^{Z \gamma} \lesssim 3.6 {\rm fb}, which requires
\sigma_{13 {\rm TeV}}^{\gamma \gamma} \lesssim 6 {\rm fb} in most of the
favored parameter space.Comment: Major changes, 17 pages, 4 figure, typos corrected, calculation
details adde
Exploring the Higgs Sector of a Most Natural NMSSM and its Prediction on Higgs Pair Production at the LHC
As a most natural realization of the Next-to Minimal Supersymmetry Standard
Model (NMSSM), {\lambda}-SUSY is parameterized by a large {\lambda} around one
and a low tan below 10. In this work, we first scan the parameter space
of {\lambda}-SUSY by considering various experimental constraints, including
the limitation from the Higgs data updated by the ATLAS and CMS collaborations
in the summer of 2014, then we study the properties of the Higgs bosons. We get
two characteristic features of {\lambda}-SUSY in experimentally allowed
parameter space. One is the triple self coupling of the SM-like Higgs boson may
get enhanced by a factor over 10 in comparison with its SM prediction. The
other is the pair production of the SM-like Higgs boson at the LHC may be two
orders larger than its SM prediction. All these features seems to be
unachievable in the Minimal Supersymmetric Standard Model and in the NMSSM with
a low {\lambda}. Moreover, we also find that naturalness plays an important
role in selecting the parameter space of {\lambda}-SUSY, and that the Higgs
obtained with the latest data is usually significantly smaller than
before due to the more consistency of the two collaboration measurements
- …