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Mark D. Goodsell

Publications and source records attributed to Mark D. Goodsell.

53 records · Page 3Linked to original sources
arXiv2016

Precision tools and models to narrow in on the 750 GeV diphoton resonance

The hints for a new resonance at 750 GeV from ATLAS and CMS have triggered a significant amount of attention. Since the simplest extensions of the standard model cannot accommodate the observation, many alternatives have been considered to explain the excess. Here we focus on several proposed renormalisable weakly-coupled models and revisit results given in the literature. We point out that physically important subtleties are often missed or neglected. To facilitate the study of the excess we have created a collection of 40 model files, selected from recent literature, for the Mathematica package SARAH. With SARAH one can generate files to perform numerical studies using the tailor-made spectrum generators FlexibleSUSY and SPheno. These have been extended to automatically include crucial higher order corrections to the diphoton and digluon decay rates for both CP-even and CP-odd scalars. Additionally, we have extended the UFO and CalcHep interfaces of SARAH, to pass the precise information about the effective vertices from the spectrum generator to a Monte-Carlo tool. Finally, as an example to demonstrate the power of the entire setup, we present a new supersymmetric model that accommodates the diphoton excess, explicitly demonstrating how a large width can be obtained. We explicitly show several steps in detail to elucidate the use of these public tools in the precision study of this model.

hep-ph↗
arXiv2015

Instanton induced Yukawa couplings from distant E3 and E(-1) instantons

We calculate non-perturbative contributions to Yukawa couplings on D3-branes at orbifold singularities due to E3 and fractional E(-1) instantons which do not intersect the visible sector branes. While distant E3 instantons on bulk cycles typically contribute to Yukawa couplings, we find that distant fractional E(-1) can also give rise to new Yukawa couplings. However, fractional E(-1) instantons only induce Yukawa couplings if they are located at a singularity which shares a collapsed homologous two-cycle with the singularity supporting the visible sector. The non-perturbative contributions to Yukawa couplings exhibit a different flavour structure than the tree-level Yukawa couplings and, as a result, they can be sources of flavour violation. This is particularly relevant for schemes of moduli stabilisation which rely on superpotential contributions from E3 instantons, such as KKLT or the Large Volume Scenario. As a byproduct of our analysis, we shed some new light on the properties of annulus diagrams with matter field insertions in stringy instanton calculus.

hep-th↗
arXiv2015

Dark matter scenarios in a constrained model with Dirac gauginos

We perform the first analysis of Dark Matter scenarios in a constrained model with Dirac Gauginos. The model under investigation is the Constrained Minimal Dirac Gaugino Supersymmetric Standard model (CMDGSSM) where the Majorana mass terms of gauginos vanish. However, $R$-symmetry is broken in the Higgs sector by an explicit and/or effective $B_μ$-term. This causes a mass splitting between Dirac states in the fermion sector and the neutralinos, which provide the dark matter candidate, become pseudo-Dirac states. We discuss two scenarios: the universal case with all scalar masses unified at the GUT scale, and the case with non-universal Higgs soft-terms. We identify different regions in the parameter space which fullfil all constraints from the dark matter abundance, the limits from SUSY and direct dark matter searches and the Higgs mass. Most of these points can be tested with the next generation of direct dark matter detection experiments.

hep-ph↗
arXiv2015

A facility to Search for Hidden Particles at the CERN SPS: the SHiP physics case

This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (Search for Hidden Particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, $τ\to 3μ$ and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the Standard Model and describe interactions between new particles and four different portals - scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the Standard Model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation

hep-ph↗
arXiv2015

Dirac Gauginos in Low Scale Supersymmetry Breaking

It has been claimed that Dirac gaugino masses are necessary for realistic models of low-scale supersymmetry breaking, and yet very little attention has been paid to the phenomenology of a light gravitino when gauginos have Dirac masses. We begin to address this deficit by investigating the couplings and phenomenology of the gravitino in the effective Lagrangian approach. We pay particular attention to the phenomenology of the scalar octets, where new decay channels open up. This leads us to propose a new simplified effective scenario including only light gluinos, sgluons and gravitinos, allowing the squarks to be heavy -- with the possible exception of the third generation. Finally, we comment on the application of our results to Fake Split Supersymmetry.

hep-ph↗
arXiv2015

Two-Loop Higgs mass calculations in supersymmetric models beyond the MSSM with SARAH and SPheno

We present an extension to the Mathematica package SARAH which allows for Higgs mass calculations at the two-loop level in a wide range of supersymmetric models beyond the MSSM. These calculations are based on the effective potential approach and include all two-loop corrections which are independent of electroweak gauge couplings. For the numerical evaluation Fortran code for SPheno is generated by SARAH. This allows the prediction of the Higgs mass in more complicated SUSY models with the same precision that most state-of-the-art spectrum generators provide for the MSSM.

hep-ph↗
arXiv2015

On the two-loop corrections to the Higgs masses in the NMSSM

We discuss the impact of the two-loop corrections to the Higgs mass in the NMSSM beyond $O(α_S(α_b + α_t))$. For this purpose we use the combination of the public tools SARAH and SPheno to include all contributions stemming from superpotential parameters. We show that the corrections in the case of a heavy singlet are often MSSM-like and reduce the predicted mass of the SM-like state by about 1 GeV as long as $λ$ is moderately large. For larger values of $λ$ the additional corrections can increase the SM-like Higgs mass. If a light singlet is present the additional corrections become more important even for smaller values of $λ$ and can even dominate the ones involving the strong interaction. In this context we point out that important effects are not reproduced quantitatively when only including $O((α_b+α_t+α_τ)^2)$ corrections known from the MSSM.

hep-ph↗
arXiv2014

A Fake Split Supersymmetry Model for the 126 GeV Higgs

We consider a scenario where supersymmetry is broken at a high energy scale, out of reach of the LHC, but leaves a few fermionic states at the TeV scale. The particle content of the low-energy effective theory is similar to that of Split Supersymmetry. However, the gauginos and higgsinos are replaced by fermions carrying the same quantum numbers but having different couplings, which we call fake gauginos and fake higgsinos. We study the prediction for the light-Higgs mass in this Fake Split SUSY Model (FSSM). We find that, in contrast to Split or high-scale supersymmetry, a 126 GeV Higgs boson is easily obtained even for arbitrarily high values of the supersymmetry scale. For a supersymmetry scale greater than roughly 100 PeV, the Higgs mass is almost independent of the supersymmetry scale and the stop mixing parameter, while the observed value is achieved for tan beta between 1.3 and 1.8 depending on the gluino mass.

hep-ph↗
arXiv2013

Hidden Photons in connection to Dark Matter

Light extra U(1) gauge bosons, so called hidden photons, which reside in a hidden sector have attracted much attention since they are a well motivated feature of many scenarios beyond the Standard Model and furthermore could mediate the interaction with hidden sector dark matter. We review limits on hidden photons from past electron beam dump experiments including two new limits from such experiments at KEK and Orsay. In addition, we study the possibility of having dark matter in the hidden sector. A simple toy model and different supersymmetric realisations are shown to provide viable dark matter candidates in the hidden sector that are in agreement with recent direct detection limits.

hep-ph↗
arXiv2013

Three- and Four-point correlators of excited bosonic twist fields

We compute three- and four-point correlation functions containing excited bosonic twist fields. Our results can be used to determine properties, such as lifetimes and production rates, of massive string excitations localised at D-brane intersections, which could be signatures of a low string scale even if the usual string resonances are inaccessible to the LHC.

hep-th↗
arXiv2012

Dirac Gauginos and the 125 GeV Higgs

We investigate the mass, production and branching ratios of a 125 GeV Higgs in models with Dirac gaugino masses. We give a discussion of naturalness, and describe how deviations from the Standard Model in the key Higgs search channels can be simply obtained. We then perform parameter scans using a SARAH package upgrade, which produces SPheno code that calculates all relevant quantities, including electroweak precision and flavour constraint data, to a level of accuracy previously impossible for this class of models. We study three different variations on the minimal Dirac gaugino extension of the (N)MSSM.

hep-ph↗
arXiv2012

Two-loop RGEs with Dirac gaugino masses

The set of renormalisation group equations to two loop order for general supersymmetric theories broken by soft and supersoft operators is completed. As an example, the explicit expressions for the RGEs in a Dirac gaugino extension of the (N)MSSM are presented.

hep-ph↗
arXiv2011

Generating mu and Bmu in models with Dirac Gauginos

We consider the extension of the Minimal Supersymmetric Standard Model by Dirac masses for the gauginos. We study the possibility that the same singlet that pairs up with the bino, to form a Dirac fermion, is used to generate mu and Bmu terms through its vacuum expectation value. For this purpose, we assume that, in the Higgs potential, the necessary R-symmetry breaking originates entirely from a superpotential term cubic in the singlet and discuss the implications for the spectrum of the model.

hep-ph↗
arXiv2007

Realistic Yukawa Couplings through Instantons in Intersecting Brane Worlds

The Yukawa couplings of the simpler models of D-branes on toroidal orientifolds suffer from the so-called ``rank one'' problem -- there is only a single non-zero mass and no mixing. We consider the one-loop contribution of E2-instantons to Yukawa couplings on intersecting D6-branes, and show that they can solve the rank one problem. In addition they have the potential to provide a geometric explanation for the hierarchies observed in the Yukawa coupling. In order to do this we provide the necessary quantities for instanton calculus in this class of background.

hep-th↗
arXiv2006

Intersecting Brane Worlds at One Loop

We develop techniques for one-loop diagrams on intersecting branes. The one-loop propagator of chiral intersection states on D6 branes is calculated exactly and its finiteness is shown to be guaranteed by RR tadpole cancellation. The result is used to demonstrate the expected softening of power law running of Yukawa couplings at the string scale. We also develop methods to calculate arbitrary N-point functions at one-loop, including those without gauge bosons in the loop. These techniques are also applicable to heterotic orbifold models.

hep-th↗
arXiv2003

The Fermionic Particle Density of Flat 1+1 Dimensional Spacetime seen by an Arbitrarily Moving Observer

A coordinate system is constructed for a general accelerating observer in 1+1 dimensions, and is used to determine the particle density of the massless Dirac vacuum for that observer. Equations are obtained for the spatial distribution and frequency distribution of massless fermions seen by this observer, in terms of the rapidity function of the observer's worldline. Examples that are considered include the uniformly accelerating observer as a limiting case, but do not always involve particle horizons. Only the low frequency limit depends on the possible presence of particle horizons. The rest of the spectrum is `almost thermal' whenever the observer's acceleration is `almost uniform'.

gr-qc↗