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A. R. Raklev

Publications and source records attributed to A. R. Raklev.

At least 19 recordsLinked to original sources
arXiv2015

An Alternative Formation Model for Antideuterons from Dark Matter

Antideuterons are a potential messenger for dark matter annihilation or decay in our own galaxy, with very low backgrounds expected from astrophysical processes. The standard coalescence model of antideuteron formation, while simple to implement, is shown to be under considerable strain by recent data from the LHC. We suggest a new empirically based model, with only one free parameter, which is better able to cope with these data, and we explore the consequences of the model for dark matter searches.

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arXiv2015

R-parity violating chargino decays at the LHC

Supersymmetric models with R-parity violation (RPV) have become more popular following the lack of any excess of missing energy events at the 8 TeV LHC. To identify such models, the suggested searches generally rely on the decay products of the (effectively) lightest supersymmetric particle (LSP), with signals that depend on the identity of the LSP and the relevant RPV operators. Here we look at the prospects for detecting RPV chargino decays at the LHC and find substantial patches of parameter space in the Minimal Supersymmetric Standard Model with possibly spectacular signatures, such as three charged-lepton resonances.

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arXiv2014

Antideuteron Limits on Decaying Dark Matter with a Tuned Formation Model

We investigate the production of antideuterons from decaying dark matter, using gravitinos in supersymmetric models with trilinear R-parity violating (RPV) operators as an example. The model used for antideuteron formation is shown to induce large uncertainties in the predicted flux, comparable to uncertainties from cosmic-ray propagation models. We improve on the formation model by tuning hadronization and coalesence parameters in Monte Carlo simulations to better reproduce the hadron spectra relevant for antideuteron production. In light of current bounds on fluxes and future prospects from the AMS-II and GAPS experiments we set limits on RPV couplings as a function of the gravitino mass.

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arXiv2014

Long lived charginos in Natural SUSY?

Supersymmetric models with a small neutralino-chargino mass difference, and as a result metastable charginos, have been a popular topic of investigation in collider phenomenology, e.g. in anomaly-mediated models of supersymmetry breaking. Recently, the absence of any supersymmetric signal at the 8 TeV LHC data has led to significant interest in the so-called Natural SUSY models with light higgsinos. These models also have a naturally small neutralino-chargino mass difference. However, we show here that when relevant indirect constraints from results at the LHC and elsewhere are applied, this possibility is heavily constrained within the Minimal Supersymmetric Standard Model (MSSM): massive metastable higgsinos are not a signature of Natural SUSY.

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arXiv2011

Boosted objects: a probe of beyond the Standard Model physics

We present the report of the hadronic working group of the BOOST2010 workshop held at the University of Oxford in June 2010. The first part contains a review of the potential of hadronic decays of highly boosted particles as an aid for discovery at the LHC and a discussion of the status of tools developed to meet the challenge of reconstructing and isolating these topologies. In the second part, we present new results comparing the performance of jet grooming techniques and top tagging algorithms on a common set of benchmark channels. We also study the sensitivity of jet substructure observables to the uncertainties in Monte Carlo predictions.

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arXiv2010

New Physics at the LHC. A Les Houches Report: Physics at TeV Colliders 2009 - New Physics Working Group

We present a collection of signatures for physics beyond the standard model that need to be explored at the LHC. First, are presented various tools developed to measure new particle masses in scenarios where all decays include an unobservable particle. Second, various aspects of supersymmetric models are discussed. Third, some signatures of models of strong electroweak symmetry are discussed. In the fourth part, a special attention is devoted to high mass resonances, as the ones appearing in models with warped extra dimensions. Finally, prospects for models with a hidden sector/valley are presented. Our report, which includes brief experimental and theoretical reviews as well as original results, summarizes the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 8-26 June, 2009).

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arXiv2010

Photon, Neutrino and Charged Particle Spectra from R-violating Gravitino Decays

We study photonic, neutrino and charged particle signatures from slow decays of gravitino dark matter in supersymmetric theories where R-parity is explicitly broken by trilinear operators. Photons and (anti-)fermions from loop and tree-level processes give rise to spectra with distinct features, which, if observed, can give crucial input on the possible mass of the gravitino and the magnitude and flavour structure of R-violating operators. Within this framework, we make detailed comparisons of the theoretical predictions to the recent experimental data from PAMELA, ATIC and Fermi LAT.

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arXiv2009

Cosmic Ray Signatures from Decaying Gravitino Dark Matter

We study the charged cosmic rays arising from the slow decay of gravitino dark matter within supersymmetric scenarios with trilinear R-parity violation. It is shown that operators of the LLE type can very well account for the recent anomalies in cosmic ray electron and positron data reported by PAMELA, ATIC and Fermi LAT, without violating any other bounds. This scenario will soon be tested by the Fermi LAT data on diffuse gamma ray emission.

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arXiv2009

Constraining the MSSM with Dark Matter indirect detection data

Recently, a claim of possible evidence for Dark Matter in data from the Fermi LAT experiment was made by Goodenough and Hooper [8]. We test the Dark Matter properties consistent with their claim in terms of the MSSM by a 24-dimensional parameter scan using nested sampling, excluding all but a very small region of the MSSM. Although this claim is very preliminary, and not made by the Fermi LAT experiment, our scan shows a possible approach for the analysis of future firm evidence from an indirect detection experiment, and its potential for heavily constraining models.

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arXiv2009

Massive Metastable Charged (S)Particles at the LHC

This brief review deals with recent interest in the prospects of observing a Massive Metastable Charged Particle (MMCP) at the Large Hadron Collider (LHC), and measuring its properties there. We discuss the motivation for scenarios with MMCPs in a phenomenological context, focusing on supersymmetric models that allow us to explore the expected experimental signatures of MMCPs at the LHC. We review current bounds and give estimates of the LHC reach in terms of MMCP masses.

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arXiv2009

Neutralino Reconstruction at the LHC from Decay-frame Kinematics

Decay-frame Kinematics (DK) has previously been introduced as a technique to reconstruct neutralino masses from their three-body decays to leptons. This work is an extension to the case of two-body decays through on-shell sleptons, with Monte Carlo simulation of LHC collisions demonstrating reconstruction of neutralino masses for the SPS1a benchmark point.

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arXiv2009

Gravitino Dark Matter and the Flavour Structure of R-violating Operators

We study gravitino dark matter and slow gravitino decays within the framework of R-violating supersymmetry, with particular emphasis on the flavour dependence of the branching ratios and the allowed R-violating couplings. The dominant decay modes and final state products turn out to be very sensitive to the R-violating hierarchies. Mixing effects can be crucial in correctly deriving the relative magnitude of the various contributions, particularly for heavy flavours with phase space suppression. The study of the strength of different decay rates for the gravitino is also correlated to collider signatures expected from decays of the Next-to-Lightest Supersymmetric Particle (NLSP) and to single superparticle production.

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arXiv2008

Physics Beyond the Standard Model: Supersymmetry

This collection of studies on new physics at the LHC constitutes the report of the supersymmetry working group at the Workshop `Physics at TeV Colliders', Les Houches, France, 2007. They cover the wide spectrum of phenomenology in the LHC era, from alternative models and signatures to the extraction of relevant observables, the study of the MSSM parameter space and finally to the interplay of LHC observations with additional data expected on a similar time scale. The special feature of this collection is that while not each of the studies is explicitely performed together by theoretical and experimental LHC physicists, all of them were inspired by and discussed in this particular environment.

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arXiv2008

Collider aspects of flavour physics at high Q

This review presents flavour related issues in the production and decays of heavy states at LHC, both from the experimental side and from the theoretical side. We review top quark physics and discuss flavour aspects of several extensions of the Standard Model, such as supersymmetry, little Higgs model or models with extra dimensions. This includes discovery aspects as well as measurement of several properties of these heavy states. We also present public available computational tools related to this topic.

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arXiv2007

Radiative gravitino decays from R-parity violation

We study radiative gravitino decay within the framework of R-violating supersymmetry. For trilinear R-violating couplings that involve the third generation of fermions, or for light gravitinos, we find that the radiative loop-decay $\tilde{G} \to γν$ dominates over the tree-level ones for a wide set of parameters. We calculate the gravitino decay width and study its implications for cosmology and collider physics. Slow-decaying gravitinos are good dark matter candidates, for a range of parameters that would also predict observable R-violating signatures in colliders. In general the branching ratios are very dependent on the relative hierarchies of R-violating operators, and may provide relevant information on the flavour structure of the underlying fundamental theory.

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arXiv2007

Reconstructing Sparticle Mass Spectra using Hadronic Decays

Most sparticle decay cascades envisaged at the Large Hadron Collider (LHC) involve hadronic decays of intermediate particles. We use state-of-the art techniques based on the \kt jet algorithm to reconstruct the resulting hadronic final states for simulated LHC events in a number of benchmark supersymmetric scenarios. In particular, we show that a general method of selecting preferentially boosted massive particles such as W, Z or Higgs bosons decaying to jets, using sub-jets found by the \kt algorithm, suppresses QCD backgrounds and thereby enhances the observability of signals that would otherwise be indistinct. Consequently, measurements of the supersymmetric mass spectrum at the per-cent level can be obtained from cascades including the hadronic decays of such massive intermediate bosons.

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arXiv2006

Mass Determination in Cascade Decays Using Shape Formulas

In SUSY scenarios with invisible LSP, sparticle masses can be determined from fits to the endpoints of invariant mass distributions. Here we discuss possible improvements by using the shapes of the distributions. Positive results are found for multiple-minima situations and for mass regions where the endpoints do not contain sufficient information to obtain the masses.

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