New regions in the NMSSM with a 125 GeV Higgs
Marcin Badziak
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Marek Olechowski
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Stefan Pokorski
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Open Access
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Institute of Theoretical Physics, Faculty of Physics, University of Warsaw
, ul. Hoz_a 69, PL-00-681 Warsaw,
Poland
It is pointed out that mixing eects in the CP-even scalar sector of the NMSSM can give 6{8 GeV correction to the SM-like Higgs mass in moderate or large tan regions with a small value of the singlet-higgs-higgs superelds coupling O (0:1). This eect comes mainly from the mixing of the SM-like Higgs with lighter singlet. In the same parameter range, the mixing of the heavy doublet Higgs with the singlet may strongly modify the couplings of the singlet-like and the 125 GeV scalars. Firstly, the LEP bounds on a light singlet can be evaded for a large range of its masses. Secondly, the decay rates of both scalars can show a variety of interesting patterns, depending on the lightest scalar mass. In particular, a striking signature of this mechanism can be a light scalar with strongly suppressed (enhanced) branching ratios to bb (gg, cc, ) as compared to the SM Higgs with the same mass. The decay channel is particularly promising for the search of such a scalar at the LHC. The 125 GeV scalar can, thus, be accommodated with substantially smaller than in the MSSM radiative corrections from the stop loops (and consequently, with lighter stops) also for moderate or large tan , with the mixing eects replacing the standard NMSSM mechanism of increasing the tree level Higgs mass in the low tan and large regime, and with clear experimental signatures of such a mechanism.
1 Introduction 2 4 5
CP-even scalar sector in NMSSM
2.1 The eects of the ^s h^ mixing on the Higgs mass
Production and decays of the 125 GeV Higgs
4.1 s with strongly suppressed couplings to b and
Prospects for discovery of s at the LHC
5.1 s with strongly suppressed couplings to b and
3 Singlet mixing with both doublets and the suppression of the sbb cou
pling
The discovery of a SM-like Higgs particle has recently been announced by the LHC
experiments [1, 2]. Although its properties such as the production and decay rates into dierent
channels still remain very uncertain [3{9], its mass is established to be around 125 GeV,
with only a couple of GeV uncertainty, and this puts new constraints on the BSM models.
In the minimal supersymmetric SM (MSSM) the Higgs tree-level quartic coupling is given
by the electroweak gauge coupling, so that the theory predicts a tree-level upper bound for
the Higgs mass to be equal MZ . It is well known that loop corrections, mainly from the
top-stop loop, can signicantly raise the Higgs mass in the MSSM. The mass of 125 GeV
can be accommodated (with loop corrections giving 35 GeV) for certain range of values
of the stop masses and left-right stop mixing parameter Xt = At tan . That range
varies from MSUSY pmt~1 mt~2 700 GeV for the \maximal" stop mixing Xt p6MSUSY
to MSUSY O (5 TeV) for Xt = 0 [10, 11].1 Such values of the stop mass parameters are
well consistent with the absence so far of any stop signal at the LHC but may look high
compared to the standard expectations based on the naturalness arguments. Awaiting
for more experimental progress, one may discard those, after all quite subjective
expectations, or one may hope that a light stop is still hidden in the data, and investigate the
ways of reconciling the 125 GeV Higgs mass with stop mass parameters below the values
1For a given value of the loop correction, the value of MSUSY depends also on other features of the SUSY
spectrum, especially on the gluino mass and the stop mass splitting, the top mass and on unknown
higherorder corrections to the Higgs mass. The value of MSUSY is particularly uncertain for MSUSY 1 TeV, see
e.g. refs. [12, 13].
quoted above. This necessarily requires a beyond MSSM scheme, with a larger tree-level
Higgs mass than in the MSSM. (It is useful to note that stop loop radiative corrections
mrhad = 25 (30) GeV can be reached with MSUSY 300 (400) GeV for the maximal mixing
and with MSUSY 1:5 (3) TeV for Xt = 0). In this context, NMSSM has been discussed in
the literature [14{20]. In the pre-discovery era, NMSSM was discussed mainly as a scenario
allowing for a Higgs mass signicantly above the values predicted by the MSSM [ 21{25].
The attention has been mostly focused on the new tree-level contribution to the Higgs
mass coming from the singlet-doublet-doublet coupling in the superpotential, SH uHd,
which can be signicant for low tan values and O(1) values of . More recently, already
after the discovery of the 125 GeV Higgs, the NMSSM has been discussed in the context of
ameliorating the naturalness in the stop sector [26{29] also mainly for the same range of
parameters. However, one may think that 125 GeV is close enough to the range expected in
the MSSM, so that small corrections to the tree-level mass are worth considering. This is
why it is interesting to investigate how signicant may be the eect of the singlet-doublet
mixing on the Higgs mass in th (...truncated)