Supersymmetry in the shadow of photini

Additional neutral gauge fermions -- "photini" -- arise in string compactifications as superpartners of U(1) gauge fields. Unlike their vector counterparts, the photini can acquire weak-scale masses from soft SUSY breaking and lead to observable signatures at the LHC through mass mixing with the bino. In this work we investigate the collider consequences of adding photini to the neutralino sector of the MSSM. Relatively large mixing of one or more photini with the bino can lead to prompt decays of the lightest ordinary supersymmetric particle; these extra cascades transfer most of the energy of SUSY decay chains into Standard Model particles, diminishing the power of missing energy as an experimental handle for signal discrimination. We demonstrate that the missing energy in SUSY events with photini is reduced dramatically for supersymmetric spectra with MSSM neutralinos near the weak scale, and study the effects on limits set by the leading hadronic SUSY searches at ATLAS and CMS. We find that in the presence of even one light photino the limits on squark masses from hadronic searches can be reduced by 400 GeV, with comparable (though more modest) reduction of gluino mass limits. We also consider potential discovery channels such as dilepton and multilepton searches, which remain sensitive to SUSY spectra with photini and can provide an unexpected route to the discovery of supersymmetry. Although presented in the context of photini, our results apply in general to theories in which additional light neutral fermions mix with MSSM gauginos.Comment: 23 pages, 8 figures, references adde

Singlet Portal to the Hidden Sector

Ultraviolet physics typically induces a kinetic mixing between gauge singlets which is marginal and hence non-decoupling in the infrared. In singlet extensions of the minimal supersymmetric standard model, e.g. the next-to-minimal supersymmetric standard model, this furnishes a well motivated and distinctive portal connecting the visible sector to any hidden sector which contains a singlet chiral superfield. In the presence of singlet kinetic mixing, the hidden sector automatically acquires a light mass scale in the range 0.1 - 100 GeV induced by electroweak symmetry breaking. In theories with R-parity conservation, superparticles produced at the LHC invariably cascade decay into hidden sector particles. Since the hidden sector singlet couples to the visible sector via the Higgs sector, these cascades necessarily produce a Higgs boson in an order 0.01 - 1 fraction of events. Furthermore, supersymmetric cascades typically produce highly boosted, low-mass hidden sector singlets decaying visibly, albeit with displacement, into the heaviest standard model particles which are kinematically accessible. We study experimental constraints on this broad class of theories, as well as the role of singlet kinetic mixing in direct detection of hidden sector dark matter. We also present related theories in which a hidden sector singlet interacts with the visible sector through kinetic mixing with right-handed neutrinos.Comment: 12 pages, 5 figure

String Photini at the LHC

String theories with topologically complex compactification manifolds suggest the simultaneous presence of many unbroken U(1)'s without any light matter charged under them. The gauge bosons associated with these U(1)'s do not have direct observational consequences. However, in the presence of low energy supersymmetry the gauge fermions associated with these U(1)'s, the "photini", mix with the Bino and extend the MSSM neutralino sector. This leads to novel signatures at the LHC. The lightest ordinary supersymmetric particle (LOSP) can decay to any one of these photini. In turn, photini may transition into each other, leading to high lepton and jet multiplicities. Both the LOSP decays and inter-photini transitions can lead to displaced vertices. When the interphotini decays happen outside the detector, the cascades can result in different photini escaping the detector leading to multiple reconstructed masses for the invisible particle. If the LOSP is charged, it stops in the detector and decays out-of-time to photini, with the possibility that the produced final photini vary from event to event. Observation of a plenitude of photini at the LHC would be evidence that we live in a string vacuum with a topologically rich compactification manifold.Comment: 23 pages, 3 figur

Naturalness and Higgs Decays in the MSSM with a Singlet

The simplest extension of the supersymmetric standard model - the addition of one singlet superfield - can have a profound impact on the Higgs and its decays. We perform a general operator analysis of this scenario, focusing on the phenomenologically distinct scenarios that can arise, and not restricting the scope to the narrow framework of the NMSSM. We reexamine decays to four b quarks and four tau's, finding that they are still generally viable, but at the edge of LEP limits. We find a broad set of Higgs decay modes, some new, including those with four gluon final states, as well as more general six and eight parton final states. We find the phenomenology of these scenarios is dramatically impacted by operators typically ignored, specifically those arising from D-terms in the hidden sector, and those arising from weak-scale colored fields. In addition to sensitivity of m_Z, there are potential tunings of other aspects of the spectrum. In spite of this, these models can be very natural, with light stops and a Higgs as light as 82 GeV. These scenarios motivate further analyses of LEP data as well as studies of the detection capabilities of future colliders to the new decay channels presented.Comment: 3 figures, 1 appendix; version to appear in JHEP; typos fixed and additional references and acknowledgements adde

Higgs, di-Higgs and tri-Higgs production via SUSY processes at the LHC with 14 TeV

We have systematically investigated the production of a Higgs boson with a mass of about $125$ GeV in the decays of supersymmetric particles within the phenomenological MSSM (pMSSM). We find regions of parameter space that are consistent with all world data and that predict a sizeable rate of anomalous Higgs, di-Higgs and even tri-Higgs events at the 14 TeV LHC. All relevant SUSY production processes are investigated. We find that Higgs bosons can be produced in a large variety of SUSY processes, resulting in a large range of different detector signatures containing missing transverse momentum. Such Higgs events are outstanding signatures for new physics already for the early 14 TeV LHC data. SUSY processes are also important to interprete deviations found in upcoming Standard Model Higgs and di-Higgs production measurements.Comment: Version submitted to JHE

Neutrino masses in quartification schemes

The idea of quark-lepton universality at high energies has recently been explored in unified theories based upon the quartification gauge group SU(3)^4. These schemes encompass a quark-lepton exchange symmetry that results upon the introduction of leptonic colour. It has been demonstrated that in models in which the quartification gauge symmetry is broken down to the standard model gauge group, gauge coupling constant unification can be achieved, and there is no unique scenario. The same is also true when the leptonic colour gauge group is only partially broken, leaving a remnant SU(2)_\ell symmetry at the standard model level. Here we perform an analysis of the neutrino mass spectrum of such models. We show that these models do not naturally generate small Majorana neutrino masses, thus correcting an error in our earlier quartification paper, but with the addition of one singlet neutral fermion per family there is a realisation of see-saw suppressed masses for the neutrinos. We also show that these schemes are consistent with proton decay.Comment: 12 pages, minor changes. To appear in Phys. Rev.

Electromagnetic cascade masquerade: a way to mimic γ\gamma--axion-like particle mixing effects in blazar spectra

Context. Most of the studies on extragalactic {\gamma}-ray propagation performed up to now only accounted for primary gamma-ray absorption and adiabatic losses ("absorption-only model"). However, there is growing evidence that this model is oversimplified and must be modified in some way. In particular, it was found that the intensity extrapolated from the optically-thin energy range of some blazar spectra is insufficient to explain the optically-thick part of these spectra. This effect was interpreted as an indication for {\gamma}-axion-like particle (ALP) oscillation. On the other hand, there are many hints that a secondary component from electromagnetic cascades initiated by primary {\gamma}-rays or nuclei may be observed in the spectra of some blazars. Aims. We study the impact of electromagnetic cascades from primary {\gamma}-rays or protons on the physical interpretation of blazar spectra obtained with imaging Cherenkov telescopes. Methods. We use the publicly-available code ELMAG to compute observable spectra of electromagnetic cascades from primary {\gamma}-rays. For the case of primary proton, we develop a simple, fast and reasonably accurate hybrid method to calculate the observable spectrum. We perform the fitting of the observed spectral energy distributions (SEDs) with various physical models: the absorption-only model, the "electromagnetic cascade model" (for the case of primary {\gamma}-rays), and several versions of the hadronic cascade model (for the case of primary proton). We distinguish the following species of hadronic cascade models: 1) "basic hadronic model", where it is assumed that the proton beam travels undisturbed by extragalactic magnetic field and that all observable {\gamma}-rays are produced by primary protons through photohadronic processes with subsequent development of electromagnetic cascades /abridgedComment: Accepted by A&A. 25 pages, 31 figures. Corrected fig. 5, fig. 7; new explanations for fig. 6--7; several typos fixed wrt v.