750 GeV diphotons from supersymmetry with Dirac gauginos

Timothy Cohen, Graham D. Kribs, Ann E. Nelson, and Bryan Ostdiek

Phys. Rev. D 94, 015031 – Published 26 July 2016

Abstract

Motivated by the recent excess in the diphoton invariant mass near 750 GeV, we explore a supersymmetric extension of the Standard Model that includes the minimal set of superpartners as well as additional Dirac partner chiral superfields in the adjoint representation for each gauge group. The bino partner pseudoscalar is identified as the 750 GeV resonance, while superpotential interactions between it and the gluino (wino) partners yield production via gluon fusion (decay to photon pairs) at one-loop. The gauginos and these additional adjoint superpartners are married by a Dirac mass and must also have Majorana masses. While a large wino partner Majorana mass is necessary to explain the excess, the gluino can be approximately Dirac-like, providing benefits consistent with being both “supersoft” (loop corrections to the scalar masses from Dirac gauginos are free of logarithmic enhancements) and “supersafe” (the experimental limits on the squark/gluino masses can be relaxed due to the reduced production rate). Consistency with the measured Standard Model–like Higgs boson mass is imposed, and a numerical exploration of the parameter space is provided. Models that can account for the diphoton excess are additionally characterized by having couplings that can remain perturbative up to very high scales, while remaining consistent with experimental constraints, the Higgs boson mass, and an electroweak scale which is not excessively fine-tuned.

Received 27 May 2016

DOI:https://doi.org/10.1103/PhysRevD.94.015031

Physics Subject Headings (PhySH)

Anomalies Particle decays Supersymmetric models

Particles & Fields

Authors & Affiliations

Timothy Cohen¹, Graham D. Kribs¹, Ann E. Nelson², and Bryan Ostdiek¹

¹Institute of Theoretical Science, University of Oregon, Eugene, Oregon 97403, USA
²Department of Physics, University of Washington, Seattle, Washington 98195, USA

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Vol. 94, Iss. 1 — 1 July 2016

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Images

Figure 1
The loop diagrams which yield the $A_{B}$ production via gluon fusion (left) and the subsequent decay to pairs of photons (right).
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Figure 2
Values of $\tan β$ and $λ_{S H H}$ which produce a 125 GeV Standard Model–like Higgs boson. The decoupling limit has been assumed. The black (blue) curves have $λ_{T H H} = 0.3$ ( $λ_{T H H} = 0$ ). Two benchmark choices for the stop masses have been chosen “light stops” $m_{{\tilde{t}}_{1}} = 750 GeV$ and $m_{{\tilde{t}}_{2}} = 900 GeV$ for the solid lines, and “very light stops” $m_{{\tilde{t}}_{1}} = 400 GeV$ and $m_{{\tilde{t}}_{2}} = 450 GeV$ for the dashed lines and the stop mixing $θ_{t} = 0$ for both. Note that the second set of benchmark values implicitly assumes that the LHC limits can be avoided by e.g. having some compression between the stops and the lightest neutralino. The thick curves are the full result for $m_{h}$ . The thin lines only include the tree-level contributions and the one-loop contributions from the stops, and neglect the loop contributions from the singlet and triplet couplings with the Higgs fields in order to demonstrate the impact of these higher order effects.
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Figure 3
Shown here are contours of $\log_{10} Λ_{Landau} / GeV$ , the scale where at least one coupling becomes nonperturbative, in the $λ_{S H H}$ versus $λ_{S T T}$ plane. The (left, middle, right) panels are for $λ_{S O O} = (0.3, 0.6, 1.2)$ . The horizontal lines denote the upper bound on the coupling due to requiring compatibility with a 125 GeV Higgs mass: $m_{{\tilde{t}}_{1}} = 750 GeV$ and $m_{{\tilde{t}}_{2}} = 900 GeV$ yields the “light stops” solid line, and $m_{{\tilde{t}}_{1}} = 400 GeV$ and $m_{{\tilde{t}}_{2}} = 450 GeV$ yields the very light stops dashed line. We have fixed $λ_{T H H} = 0.3$ in this figure.
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Figure 4
The contours display $\log_{10}$ of the scale at which a supersymmetric coupling becomes nonperturbative. The left (right) panel has $λ_{S O O} = 0.6$ ( $λ_{S O O} = 1.2$ ). The blue area is capable of producing a signal rate within the $2 σ$ best fit region defined by [9]. The orange region is capable of producing a signal within $1 σ$ of the best-fit value. The red region can produce a signal that is larger than $1 σ$ above the best fit signal, such that it is straightforward to find parameters which produce the observed rate. The purple boxes and green diamonds denote benchmarks that are studied in more detail in this section, the former are chosen to emphasize naturalness while the later have Landau poles which are postponed to near the GUT scale (and also have accompanying Fig. 5). The horizontal lines denote the upper bound on the coupling due to requiring compatibility with a 125 GeV Higgs mass: $m_{{\tilde{t}}_{1}} = 750 GeV$ and $m_{{\tilde{t}}_{2}} = 900 GeV$ yields the light stops solid line, and $m_{{\tilde{t}}_{1}} = 400 GeV$ and $m_{{\tilde{t}}_{2}} = 450 GeV$ yields the very light stops dashed line. We have fixed $λ_{T H H} = 0.3$ in this figure. The minimum gluino mass considered in these plots is 1.5 TeV. The shapes are not exact, with a grid step size of 0.2, and the value at each point coming from the maximization algorithm depending on random sampling.
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Figure 5
Signal rate as a function of the lightest chargino (gluino) mass are given in the top (bottom) row. The left (right) panel has a small (large) value for the singlet-octet coupling. The $1 σ$ ( $2 σ$ ) region that is consistent with the diphoton excess [9] is shaded in orange (blue). We have fixed $λ_{T H H} = 0.3$ in this figure. These points correspond to the green diamonds in Fig. 4, and were chosen to realize models with a high scale Landau pole. Heavier masses that are compatible with the signal can be realized at the expense of a lower cutoff.
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