We extend the Standard Model gauge group by a gauged
U(1)
R
R-symmetry or a gauged
U(1)′. The requirement of cancellation of anomalies is very constraining but can be achieved by adding three or four ...hidden-sector fields which are Standard Model singlets. The
U(1)
R
or
U(1)′ quantum numbers of these singlets are usually large producing a nonrenormalisable superpotential with a high power in the singlet fields. We have minimized the supergravity scalar potential and have found solutions where the vacuum expectation values of all hidden-sector singlet fields are less than the Planck mass
<z
m> = O(
M
Pl
10
)
. This produces the small supersymmetry scale of order the weak scale from only the Planck scale. The mu problem is simultaneously solved in this manner.
We propose a new method of detecting supersymmetry at LEP2 and the NLC when R-parity is violated by an
LL
E
̄
operator. We consider the processes
eγ→
ν
̃
je
k
and
eγ→
l
̃
k
ν
̄
j
which can test seven ...of the nine
LL
E
̄
-operators. A Monte Carlo analysis is performed to investigate the sensitivity to the sneutrino signal, and the 5
σ discovery contours in the
m
ν
̃
j
vs.
λ plane are presented. For an integrated luminosity of
100
pb
−1
, sneutrinos with masses up to
M
ν
̃
<170
GeV/c
2
could be discovered in the near future at LEP2. For the charged slepton production the cross-section is too low to be detectable.
We study the pair production of charginos in
e
+e
−
-collisions followed by the decay via R-parity violating
LQ
D
operators. We determine the complete matrix element squared for chargino decays via
...LQ
D
or
LL
E
operators. We find regions in MSSM parameter space where the chargino mass is 52.5 GeV and the R-parity violating decays of the charginos dominate the gauge decays to neutralinos. At LEP2 this then leads to additional 4 jet events which could explain the excess recently observed by ALEPH.
We study the possible LHC collider signatures in the next-to-minimal supersymmetric Standard Model (NMSSM). The general NMSSM consists of 29 supersymmetric (SUSY) particles which can be mass ordered ...in \(29! \simeq 9 \cdot 10^{30}\) ways. To reduce the number of hierarchies to a more manageable amount we assume a degeneracy of the sfermions of the first two generations with the same quantum numbers. Further assumptions about the neutralino and chargino masses leave 15 unrelated parameters. We check all \(15! \approx 10^{12}\) relevant mass orderings for the dominant decay chains and the corresponding collider signatures at the LHC. As preferred signatures, we consider charged leptons, missing transverse momentum, jets, and W, Z or Higgs bosons. We present the results for three different choices of the singlet to Higgs coupling \(\lambda\): (a) small: \(O(\lambda)< O(Y_{\tau})\), (b) large: \(O(\lambda)\simeq O(Y_{top},Y_b, Y_\tau)\) and (c) dominant: \(O(\lambda)>O(Y_{top})\). We compare these three scenarios with the MSSM expectations as well as among each other. We also mention a possible mass hierarchy leading to 7 jets plus 1 lepton signatures at the LHC and comment briefly on the consequence of possible R-parity violation.
In order to accommodate the observed Higgs boson mass in the CMSSM, the stops must either be very heavy or the mixing in the stop sector must be very large. Lower stop masses, possibly more ...accessible at the LHC, still give the correct Higgs mass only if the trilinear stop mixing parameter \(|A_t|\) is in the multi-TeV range. Recently it has been shown that such large stop mixing leads to an unstable electroweak vacuum which spontaneously breaks charge or colour. In this work we therefore go beyond the CMSSM and investigate the effects of including baryon number violating operators \(\lambda'' \bar{\bf U} \bar{\bf D}\bar{\bf D}\) on the stop and Higgs sectors. We find that for \(\lambda'' \simeq {\mathcal{O}}(0.3)\) light stop masses as low as 220 GeV are consistent with the observed Higgs mass as well as flavour constraints while allowing for a stable vacuum. The light stop in this scenario is often the lightest supersymmetric particle. We furthermore discuss the importance of the one-loop corrections involving R-parity violating couplings for a valid prediction of the light stop masses.
We consider the ATLAS and CMS searches for dijet resonances, as well as the ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center of mass energy. We interpret their exclusions in terms ...of bounds on the supersymmetric R-parity violating parameter space. For this we focus on resonant slepton production followed by the corresponding decay.
R -parity violating minimal supergravity model Allanach, B. C.; Dedes, A.; Dreiner, H. K.
Physical review. D, Particles, fields, gravitation, and cosmology,
06/2004, Letnik:
69, Številka:
11
Journal Article
Odprti dostop
We present the minimal supersymmetric standard model with general broken R-parity, focusing on minimal supergravity (mSUGRA). We discuss the origins of lepton number violation in supersymmetry. We ...have computed the full set of coupled one-loop renormalization group equations for the gauge couplings, the superpotential parameters and for all the soft supersymmetry breaking parameters. We provide analytic formule for the scalar potential minimization conditions which may be iterated to arbitrary precision. We compute the low-energy spectrum of the superparticles and the neutrinos as a function of the small set of parameters at the unification scale in the general basis. Specializing to mSUGRA, we use the neutrino masses to set new bounds on the R-parity violating couplings. These bounds are up-to five orders of magnitude stricter than the previously existing ones. In addition, new bounds on the R-parity violating couplings are also derived demanding a non-tachyonic sneutrino spectrum. We investigate the nature of the lightest supersymmetric particle and find extensive regions in parameter space, where it is not the neutralino. This leads to a novel set of supersymmetric signatures, which we classify.
We consider first an interesting connection between the development of physics and the Boston Red Sox. We then discuss in detail the collider phenomenology, as well as precision electroweak ...observables of a very light neutralino. We conclude by considering also the astrophysics and cosmology of a very light neutralino. We find that a massless neutralino is consistent with all present data.
Physics with e+e− linear colliders Accomando, E.; Andreazza, A.; Ballestrero, A. ...
Physics reports,
06/1998, Letnik:
299, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The physics potential of
e
+
e
− linear colliders is summarized in this report. These machines are planned to operate in the first phase at a center-of-mass energy of 500
GeV, before being scaled up ...to about 1
TeV. In the second phase of the operation, a final energy of about 2
TeV is expected. The machines will allow us to perform precision tests of the heavy particles in the Standard Model, the top quark and the electroweak bosons. They are ideal facilities for exploring the properties of Higgs particles, in particular in the intermediate mass range. New vector bosons and novel matter particles in extended gauge theories can be searched for and studied thoroughly. The machines provide unique opportunities for the discovery of particles in supersymmetric extensions of the Standard Model, the spectrum of Higgs particles, the supersymmetric partners of the electroweak gauge and Higgs bosons, and of the matter particles. High precision analyses of their properties and interactions will allow for extrapolations to energy scales close to the Planck scale where gravity becomes significant. In alternative scenarios, i.e. compositeness models, novel matter particles and interactions can be discovered and investigated in the energy range above the existing colliders up to the TeV scale. Whatever scenario is realized in Nature, the discovery potential of
e
+
e
− linear colliders and the high precision with which the properties of particles and their interactions can be analyzed, define an exciting physics program complementary to hadron machines.
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