Searching for L-violating supersymmetry at the LHC

The possibility to simulate lepton number violating supersymmetric models has been introduced into the recently updated Pythia event generator, now containing 1278 decay channels of SUSY particles into SM particles via lepton number violating interactions. This generator has been used in combination with the AtlFast detector simulation to study the impact of lepton number violation () on event topologies in the ATLAS detector, and trigger menus designed for -SUSY are proposed based on very general considerations. In addition, a rather preliminary analysis is presented on the possibility for ATLAS to observe a signal above the background in several mSUGRA scenarios, using a combination of primitive cuts and neural networks to optimize the discriminating power between signal and background events over regions of parameter space rather than at individual points. It is found that a discovery is possible roughly for TeV and TeV with an integrated luminosity of 30 fb, corresponding to one year of data taking with the LHC running at “mid-luminosity”, cms. Received: 5 October 2001 / Revised version: 20 November 2001 / Published online: 18 January 2002     

Searching for supersymmetry at LEP/LHC

For theep collider at LEP/LHC, we study the production and the signal coming from sleptons and squarks for several processes. We show how the supersymmetric signal can be extracted from the Standard Model background processes. In particular the large backgrounds due to singleW andZ production are considered. All the results are based on exact calculations of the matrix elements at tree level. Total cross sections and various kinematical distributions are presented.     

Searching for signatures of supersymmetry at B-factories

We analyze the predictions for CP asymmetries in B⁰-meson decays within the framework of the supersymmetric standard model (SSM). It is pointed out that owing to sizable new contributions to B_d⁰−B⁰_d and K⁰−K⁰ mixings, the experimentally allowed range for the CP-violating phase δ of the Cabibbo-Kobayashi-Maskawa matrix may be different from the one obtained in the standard model (SM). This has important effects on the allowed values of CP asymmetries in B⁰-meson decays and on their correlations. We calculate the ratio R of the SSM and the SM contributions to the B⁰d–B⁰_d mixing parameter x_d and discuss in detail the ranges of R and S which are consistent with the experimental values of x_d and the CP violation parameter ϵ for K⁰–K⁰ mixing. The CP asymmetries are predicted to have values different from the SM_predictions in sizable regions of parameter space. We also discuss the SSM predictions for B⁰_s–B⁰_s mixing.     

Searching for the spin-0 leptons of supersymmetry

The production and subsequent decay of spin-0 electrons and muons in e⁺e^? annihilation leads to distinctive noncoplanar e⁺e^? or μ⁺μ^? production, with missing energy carried away by photinos or goldstinos. We give the cross section predicted by supersymmetry for creating pairs of these new spin-0 particles. Present e⁺e^? annihilation experiments imply that their masses must be larger than $\text{3}\text{1}\text{2}\text{GeV}\text{/c}{}^2$, and in the near future PETRA experiments will either observe them or raise this limit to ～15 GeV/c².     

Polynomial supersymmetry for matrix Hamiltonians

We study intertwining relations for matrix non-Hermitian Hamiltonians by matrix differential operators of arbitrary order. It is established that for any intertwining operator of minimal order there is operator that intertwines the same Hamiltonians in the opposite direction and such that the products of these operators are identical polynomials of the corresponding Hamiltonians. The related polynomial algebra of supersymmetry is constructed. The problems of minimization and reducibility of a matrix intertwining operator are considered and the criteria of minimizability and reducibility are presented. It is shown that there are absolutely irreducible matrix intertwining operators, in contrast to the scalar case.     

Local supersymmetry for spinning particles

First and second order forms of the covariant action for a spinning particle are exhibited. The action consistently incorporates the necessary constraints and is invariant under both local supersymmetry and general time parameter transformations, and provides a simple one-dimensional model for the interaction between matter and supergravity. A formulation invariant under general co-ordinate transformations in superspace is also given and shown to be equivalent to the locally supersymmetric one.     

Proposed Post-LEP benchmarks for supersymmetry

We propose a new set of supersymmetric benchmark scenarios, taking into account the constraints from LEP, and cosmology. We work in the specific context of the constrained MSSM (CMSSM) with universal soft supersymetry-breaking masses and vanishing trilinear terms, assuming that R parity is conserved. We propose benchmark points that exemplify the different generic possibilities in this context, including focus-point models, points where coannihilation effects on the relic density are important, and points with rapid relic annihilation via direct-channel Higgs poles. We discuss the principal decays and signatures of the different classes of benchmark scenarios, and make initial estimates of the physics reaches of different accelerators, including the Tevatron collider, the LHC, and colliders in the sub- and multi-TeV ranges. We stress the complementarity of hadron and lepton colliders, with the latter favoured for non-strongly-interacting particles and precision measurements. We mention features that could usefully be included in future versions of supersymmetric event generators. Received: 28 June 2001 / Revised version: 12 September 2001 / Published online: 23 November 2001     

Search for supersymmetry at LHC

One of the main motivations for the experiments at the Large Hadron Collider (LHC), scheduled to start around 2006, is to search for supersymmetric particles. The region of the parameter space of the minimal supersymmetric standard model, where supersymmetry can be discovered, is investigated. We show that if supersymmetry exists at the electroweak scale, it would be easy to find signals for it at the LHC. If the LHC does find supersymmetry, this would be one of the greatest achievements in the history of theoretical physics.     

One-parameter nonrelativistic supersymmetry for microtubules

The one-parameter nonrelativistic supersymmetry of Mielnik [J. Math. Phys. 25 (1984) 3387] is applied to the simple supersymmetric model of Caticha [Phys. Rev. A 51 (1995) 4264] in the form used by Rosu [Phys. Rev. E 55 (1997) 2038] for microtubules. By this means, we introduce Montroll double-well potentials with singularities that move along the positive or negative traveling direction depending on the sign of the free parameter of Mielnik's method. Possible interpretations of the singularity are either microtubule associated proteins (motors) or structural discontinuities in the arrangement of the tubulin molecules.     

Updated post-WMAP benchmarks for supersymmetry

We update a previously-proposed set of supersymmetric benchmark scenarios, taking into account the precise constraints on the cold dark matter density obtained by combining WMAP and other cosmological data, as well as the LEP and constraints. We assume that R parity is conserved and work within the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking scalar and gaugino masses m₀ and m_1/2. In most cases, the relic density calculated for the previous benchmarks may be brought within the WMAP range by reducing slightly m₀, but in two cases more substantial changes in m₀ and m_1/2 are made. Since the WMAP constraint reduces the effective dimensionality of the CMSSM parameter space, one may study phenomenology along WMAP lines in the (m_1/2, m₀) plane that have acceptable amounts of dark matter. We discuss the production, decays and detectability of sparticles along these lines, at the LHC and at linear e ⁺ e^- colliders in the sub- and multi-TeV ranges, stressing the complementarity of hadron and lepton colliders, and with particular emphasis on the neutralino sector. Finally, we preview the accuracy with which one might be able to predict the density of supersymmetric cold dark matter using collider measurements.Received: 2 September 2003, Published online: 4 February 2004     

Fractional supersymmetry as a superposition of ordinary supersymmetry

It is shown how to derive fractional supersymmetric quantum mechanics of order k as a superposition of k-1 copies of ordinary supersymmetric quantum mechanics.     

Unconstrained supersymmetry

This is a first step towards better superfield formulations of supersymmetric field theories. The simple Wess-Zumino model (including renormalizable interactions) is formulated in terms of an unconstrained, scalar superfield, obeying a wave equation that includes the square of the super Klein-Gordon operator. This wave equation is derived from an action principle, by unconstrained variation of the superfield. The physical content of the theory is the same as for the original formulation by Wess and Zumino, and the Feynman rules are identical to those of Grisaru, Roek and Siegel. Next, super electrodynamics, including minimal interactions with a scalar matter multiplet, is given a similar treatment. There is no need, in this case, to include higher derivatives in the Lagrangian. The matter field is an unconstrained, scalar superfield, and the gauge fields are also contained in an unconstrained, scalar superfield. The scattering matrix coincides with that of the conventional form of super electrodynamics with Wess-Zumino matter fields. Supersymmetric spinorial currents are found by simple and direct application of the Noetherian method, in superfield language. Conservation laws of the formD _a J ^a =0 (resp.D _a J ^ab =0) are derived from gauge invariance (resp. supersymmetry). Extension to super Yang-Mills theories is straightforward.On leave of absence from Universidad Complutense, Madrid. Permanent address: Department of Theoretical Physics, Universidad Complutense, 28040 Madrid, Spain.     

Low-energy supersymmetry

We discuss the problem of constructing a model in which supersymmetry is unbroken down to low energies. It is suggested that the scalar partners of quarks and leptons may get their masses through radiative corrections and that the breaking of the weak interactions also occurs through radiative corrections. A toy model is constructed which illustrates these ideas.     

Secret supersymmetry

We present new non-linear realizations of the N = 1 supergravity algebra. They allow us to build interesting realistic models of the four forces of nature. These models are different from all previous ones in that particles do not appear in (broken) supersymmetric multiplets.These new non-linear realizations also permit us to construct the effective low-energy lagrangian of an arbitrary supergravity theory in which supersymmetry is spontaneously broken. We are thus able to analyze what are the model-independent low-energy effects of supergravity. We find that the number of Higgs fields and the way they couple to quark and lepton matter is a feature which distinguishes supersymmetric theories from non-supersymmetric ones.     

Search for supersymmetry in light nuclei

The supersymmetry assumption based on a system of valence interacting bosons and odd nucleons has been checked in the second half of the nuclear sd-shell. The dynamical supersymmetric hamiltonian restricted to the linear combination of chosen second-order Casimir invariants has been applied to energy levels of several nuclei organized in supermultiplets. The supersymmetry predictions for nine nuclei are in accord, to a good approximation, with experimental energy levels up to 4–7 MeV.     

Measuring supersymmetry

If new physics is found at the LHC (and the ILC) the reconstruction of the underlying theory should not be biased by assumptions about high-scale models. For the mapping of many measurements onto high-dimensional parameter spaces we introduce SFitter with its new weighted Markov chain technique. SFitter constructs an exclusive likelihood map, determines the best-fitting parameter point and produces a ranked list of the most likely parameter points. Using the example of the TeV-scale supersymmetric Lagrangian we show how a high-dimensional likelihood map will generally include degeneracies and strong correlations. SFitter allows us to study such model-parameter spaces employing Bayesian as well as frequentist constructions. We illustrate in detail how it should be possible to analyze high-dimensional new-physics parameter spaces like the TeV-scale MSSM at the LHC. A combination of LHC and ILC measurements might well be able to completely cover highly complex TeV-scale parameter spaces.     

Hidden supersymmetry

Inspired by the concept of complementarity, we present a illustrative model for the weak interactions with unbroken gauge symmetry and unbroken supersymmetry. The observable particles are bound states of some more fundamental particles. Supersymmetry is broken at the macroscopic scale of the observable particles by a discrete symmetry but remains exact at the scale of the fundamental particle and is thus hidden. This provides a link between theories at very high energies and the observed particle physics. Supersymmetric particles are confined in usual matter.     

Search for supersymmetry at LEP-2

An extensive effort to search for a hint of a supersymmetric signal was carried out by the four LEP Collaborations. All LEP data, up to centre-of-mass energy of 209 GeV, was carefully analysed with no observed SUSY signal. In an attempt to further increase the sensitivity of the search, the four groups combined some of their searches, to no avail.