78 research outputs found
Testing the Mechanism for the LSP Stability at the LHC
The lightest supersymmetric particle (LSP) is a natural candidate for the
cold dark matter of the universe. In this Letter we discuss how to test the
mechanism responsible for the LSP stability at the LHC. We note that if
R-parity is conserved dynamically one should expect a Higgs boson which decays
mainly into two right-handed neutrinos (a "leptonic" Higgs) or into two
sfermions. The first case could exhibit spectacular lepton number violating
signals with four secondary vertices due to the long-lived nature of
right-handed neutrinos. These signals, together with the standard channels for
the discovery of SUSY, could help to establish the underlying theory at the TeV
scale.Comment: 4 pages, 3 figures, 1 table, minor corrections, published in Physics
Letters
Grand Unification and Light Color-Octet Scalars at the LHC
We study the properties and production mechanisms of color-octet scalars at
the LHC. We focus on the single production of both charged and neutral members
of an (8,2)_1/2 doublet through bottom quark initial states. These channels
provide a window to the underlying Yukawa structure of the scalar sector.
Color-octet scalars naturally appear in grand unified theories based on the
SU(5) gauge symmetry. In the context of adjoint SU(5) these fields are expected
to be light to satisfy constraints coming from unification and proton decay,
and may have TeV-scale masses. One combination of their couplings is defined by
the relation between the down-quark and charged-lepton Yukawa couplings.
Observation of these states at the LHC gives an upper bound on the proton
lifetime if they truly arise from this grand unified theory. We demonstrate
that TeV-mass scalars can be observed over background at the LHC using boosted
top quark final states, and study how well the scalar Yukawa parameters can be
measured.Comment: 22 pages, LaTeX, 5 figures; typos corrected, references adde
Dark Matter and the Seesaw Scale
We discuss the possibility of finding an upper bound on the seesaw scale using the cosmological bound on the cold dark matter relic density. We investigate a simple relation between the origin of neutrino masses and the properties of a dark matter candidate in a simple theory where the new symmetry breaking scale defines the seesaw scale. Imposing the cosmological bounds, we find an upper bound of order multi-TeV on the lepton number violation scale. We investigate the predictions for direct and indirect detection dark matter experiments and the possible signatures at the Large Hadron Collider
Minimal gauged U(1)_{B-L} model with spontaneous R-parity violation
We study the minimal gauged U(1)_{B-L} supersymmetric model and show that it
provides an attractive theory for spontaneous R-parity violation. Both
U(1)_{B-L} and R-parity are broken by the vacuum expectation value of the
right-handed sneutrino (proportional to the soft SUSY masses), thereby linking
the B-L and soft SUSY scales. In this context we find a consistent mechanism
for generating neutrino masses and a realistic mass spectrum, all without
extending the Higgs sector of the minimal supersymmetry standard model. We
discuss the most relevant collider signals and the connection between the Z'
gauge boson and R-parity violation.Comment: 4 pages, new title, to appear in Physical Review Letter
Higgs boson decays, baryon number violation, and supersymmetry at the LHC
Baryon number violating interactions could modify the signatures of supersymmetric models at the Large Hadron Collider. In this article we investigate the predictions for the Higgs mass and the Higgs decays in a simple extension of the minimal supersymmetric standard model where the local baryon and lepton numbers are spontaneously broken at the TeV scale. This theory predicts baryon number violation at the low scale which can change the current LHC bounds on the supersymmetric spectrum. Using the ATLAS and CMS bounds on the Higgs mass we show the constraints on the sfermion masses, and show the subsequent predictions for the radiative Higgs decays. We found that the Higgs decay into two photons is suppressed due to the existence of new light leptons. In this theory the stops can be very light in agreement with all experimental bounds and we make a brief discussion of the possible signals at the LHC
Gauge Theory for Baryon and Lepton Numbers with Leptoquarks
Models where the baryon (B) and lepton (L) numbers are local gauge symmetries that are spontaneously
broken at a low scale are revisited. We find new extensions of the standard model which predict
the existence of fermions that carry both baryon and lepton numbers (i.e., leptoquarks). The local baryonic
and leptonic symmetries can be broken at a scale close to the electroweak scale and we do not need to
postulate the existence of a large desert to satisfy the experimental constraints on baryon number violating
processes like proton decay
Triplet scalars and dark matter at the LHC
We investigate the predictions of a simple extension of the standard model where the Higgs sector is composed of one SU(2)L doublet and one real triplet. We discuss the general features of the model, including its vacuum structure, theoretical and phenomenological constraints, and expectations for Higgs collider studies. The model predicts the existence of a pair of light charged scalars and, for vanishing triplet vacuum expectation value, contains a cold dark matter candidate. When the latter possibility occurs, the charged scalars are long-lived, leading to a prediction of distinctive single charged track with missing transverse energy or double charged track events at the large hadron collider. The model predicts a significant excess of two-photon events compared to SM expectations due to the presence of a light charged scalar
Seesaw scale, unification, and proton decay
We investigate a simple realistic grand unified theory based on the SU(5) gauge symmetry, which predicts an upper bound on the proton decay lifetime for the channels p→K+ν¯ and p→π+ν¯, i.e., τ(p→K+ν¯)≲3.4×1035 and τ(p→π+ν¯)≲1.7×1034  years, respectively. In this context, the neutrino masses are generated through the type I and type III seesaw mechanisms, and one predicts that the field responsible for type III seesaw must be light with a mass below 500 TeV. We discuss the testability of this theory at current and future proton decay experiments
Spontaneous R-Parity Breaking and Left-Right Symmetry
We propose a simple renormalizable left-right theory where R-parity is
spontaneously broken and neutrino masses are generated through the Type I
seesaw mechanism and R-parity violation. In this theory R-parity and the gauge
symmetry are broken by the sneutrino vacuum expectation values and there is no
Majoron problem. The SU(2)_R and R-parity violation scales are determined by
the SUSY breaking scale making the model very predictive. We discuss the
spectrum and possible tests of the theory through the neutralinos, charginos,
Z^' and W_R decays at the Large Hadron Collider.Comment: 4 pages, minor corrections, title changed, to appear in Physics
Letters
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