arXiv subjects

Christopher B. Verhaaren

Publications and source records attributed to Christopher B. Verhaaren.

42 records · Page 3Linked to original sources

arXiv2016

Quirky Explanations for the Diphoton Excess

We propose two simple quirk models to explain the recently reported 750 GeV diphoton excesses at ATLAS and CMS. It is already well-known that a real singlet scalar $ϕ$ with Yukawa couplings $ϕ\bar X X$ to vector-like fermions $X$ with mass $m_X > m_ϕ/2$ can easily explain the observed signal, provided $X$ carries both SM color and electric charge. We instead consider first the possibility that the pair production of a fermion, charged under both SM gauge groups and a confining $SU(3)_v$ gauge group, is responsible. If pair produced it forms a quirky bound state, which promptly annihilates into gluons, photons, v-gluons and possibly SM fermions. This is an extremely minimal model to explain the excess, but is already in some tension with existing displaced searches, as well as dilepton and dijet resonance bounds. We therefore propose a hybrid Quirk-Scalar model, in which the fermion of the simple $ϕ\bar X X$ toy model is charged under the additional $SU(3)_v$ confining gauge group. Constraints on the new heavy fermion $X$ are then significantly relaxed. The main additional signals of this model are possible dilepton, dijet and diphoton resonances at $\sim$ 2 TeV or more from quirk annihilation, and the production of v-glueballs through quirk annihilation and $ϕ$ decay. The glueballs can give rise to spectacular signatures, including displaced vertices and events with leptons, photons and $Z$-bosons. If the Quirk-Scalar model is responsible for the 750 GeV excess it should be discovered in one of these channels with 20 or $300 \mathrm{fb}^{-1}$ of LHC run 2 data.

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arXiv2015

Putting a Stop to di-Higgs Modifications

Pair production of Higgs bosons at hadron colliders is an enticing channel to search for new physics. New colored particles that couple strongly to the Higgs, such as those most often called upon to address the hierarchy problem, provide well motivated examples in which large enhancements of the di-Higgs rate are possible, at least in principle. However, in such scenarios the di-Higgs production rate is tightly correlated with the single Higgs production rate and, since the latter is observed to be SM-like, one generally expects that only modest enhancements in di-Higgs production are allowed by the LHC Run 1 data. We examine the contribution of top squarks (stops) in a simplified supersymmetry model to di-Higgs production and find that this general expectation is indeed borne out. In particular, the allowed deviations are typically small, but there are tuned regions of parameter space where expectations based on EFT arguments break down in which order 100% enhancements to the di-Higgs production rate are possible and are simultaneously consistent with the observed single Higgs production rates. These effects are potentially observable with the high luminosity run of the LHC or at a future hadron collider.

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arXiv2015

Interactions of a Stabilized Radion and Duality

We determine the couplings of the graviscalar radion in Randall-Sundrum models to Standard Model fields propagating in the bulk of the space, taking into account effects arising from the dynamics of the Goldberger-Wise scalar that stabilizes the size of the extra dimension. The leading corrections to the radion couplings are shown to arise from direct contact interactions between the Goldberger-Wise scalar and the Standard Model fields. We obtain a detailed interpretation of the results in terms of the holographic dual of the radion, the dilaton. In doing so, we determine how the familiar identification of the parameters on the two sides of the AdS/CFT correspondence is modified in the presence of couplings of the bulk Standard Model fields to the Goldberger-Wise scalar. We find that corrections to the form of the dilaton couplings from effects associated with the stabilization of the extra dimension are suppressed by the square of the ratio of the dilaton mass to the Kaluza-Klein scale, in good agreement with results from the CFT side of the correspondence.

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arXiv2015

A Couplet from Flavored Dark Matter

We show that a couplet, a pair of closely spaced photon lines, in the X-ray spectrum is a distinctive feature of lepton flavored dark matter models for which the mass spectrum is dictated by Minimal Flavor Violation. In such a scenario, mass splittings between different dark matter flavors are determined by Standard Model Yukawa couplings and can naturally be small, allowing all three flavors to be long-lived and contribute to the observed abundance. Then, in the presence of a tiny source of flavor violation, heavier dark matter flavors can decay via a dipole transition on cosmological timescales, giving rise to three photon lines. The ratios of the line energies are completely determined in terms of the charged lepton masses, and constitute a firm prediction of this framework. For dark matter masses of order the weak scale, the couplet lies in the keV-MeV region, with a much weaker line in the eV-keV region. This scenario constitutes a potential explanation for the recent claim of the observation of a 3.5 keV line. The next generation of X-ray telescopes may have the necessary resolution to resolve the double line structure of such a couplet.

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arXiv2015

Colorless Top Partners, a 125 GeV Higgs, and the Limits on Naturalness

Theories of physics beyond the Standard Model that address the hierarchy problem generally involve top partners, new particles that cancel the quadratic divergences associated with the Yukawa coupling of the Higgs to the top quark. With extensions of the Standard Model that involve new colored particles coming under strain from collider searches, scenarios in which the top partners carry no charge under the strong interactions have become increasingly compelling. Although elusive for direct searches, these theories predict modified couplings of the Higgs boson to the Standard Model particles. This results in corrections to the Higgs production and decay rates that can be detected at the Large Hadron Collider (LHC) provided the top partners are sufficiently light, and the theory correspondingly natural. In this paper we consider three theories that address the little hierarchy problem and involve colorless top partners, specifically the Mirror Twin Higgs, Folded Supersymmetry, and the Quirky Little Higgs. For each model we investigate the current and future bounds on the top partners, and the corresponding limits on naturalness, that can be obtained from the Higgs program at the LHC. We conclude that the LHC will not be able to strongly disfavor naturalness, with mild tuning at the level of about one part in ten remaining allowed even with 3000 fb$^{-1}$ of data at 14 TeV.

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arXiv2014

Leptophilic Dark Matter and the Anomalous Magnetic Moment of the Muon

We consider renormalizable theories such that the scattering of dark matter off leptons arises at tree level, but scattering off nuclei only arises at loop. In this framework, the various dark matter candidates can be classified by their spins and by the forms of their interactions with leptons. We determine the corrections to the anomalous magnetic moment of the muon that arise from these interactions. We then consider the implications of these results for a set of simplified models of leptophilic dark matter. When a dark matter candidate reduces the existing tension between the standard model prediction of the anomalous magnetic moment and the experimental measurement, the region of parameter space favored to completely remove the discrepancy is highlighted. Conversely, when agreement is worsened, we place limits on the parameters of the corresponding simplified model. These bounds and favored regions are compared against the experimental constraints on the simplified model from direct detection and from collider searches. Although these constraints are severe, we find there do exist limited regions of parameter space in these simple theories that can explain the observed anomaly in the muon magnetic moment while remaining consistent with all experimental bounds.

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