Strongly Interacting Massive Particle Research Articles

SIMPly add a dark photon

Pions of a dark sector gauge group can be strongly interacting massive particle (SIMP) dark matter, produced by the freeze-out of 3 → 2 interactions, with naturally large self-interactions. We study if adding a dark photon to the set-up can do it all: i) maintain thermalization with the visible sector, ii) resonantly enhance the 3 → 2 interactions, thus allowing for a perturbative pion description, and iii) provide a velocity dependent self-interaction that can affect small scale structure formation. For Nf = 3 this minimal setup is marginally excluded, as the required kinetic mixing is too small to maintain thermal equilibrium with the SM. Adding an extra dark quark opens up parameter space, and — perhaps somewhat surprisingly — we find that all bounds can be satisfied for dark pion masses mπ ∼ 250 − 600 MeV. Dropping the small scale structure requirement iii), a viable setup is reproduced for dark charges of αd = 0.01 − 1 and a dark pion mass mπ ≥ 30 MeV. Late time annihilations are non-negligible making the SIMP dark pion a bit WIMPy.

SIMP Dark Matter

These notes summarize the zoom-course on Strongly Interacting Massive Particle (SIMP) dark matter given at the Les Houches Summer School in the summer of 2021. An alternative title for this course would be `SIMPS, Cannibals and ELDERs', where our focus is on high-point interactions amongst dark matter particles. The spirit of the course is to give students a taste of these exciting developments in dark matter, while primarily teaching tricks and methods that are tough to captivate when reading textbooks or papers. These notes are written in similar spirit: I will put emphasis on how quantities scale and how to perform back of the envelope estimates, which should serve to help you when you develop the next great dark matter idea.

A multi-component SIMP model with U(1)X\u2192 Z2 \xd7 Z3

Multi-component dark matter scenarios are studied in the model with U(1)X dark gauge symmetry that is broken into its product subgroup Z2 × Z3 á la Krauss-Wilczek mechanism. In this setup, there exist two types of dark matter fields, X and Y, distinguished by different Z2 × Z3 charges. The real and imaginary parts of the Z2-charged field, XR and XI, get different masses from the U(1)X symmetry breaking. The field Y, which is another dark matter candidate due to the unbroken Z3 symmetry, belongs to the Strongly Interacting Massive Particle (SIMP)-type dark matter. Both XI and XR may contribute to Y’s 3 → 2 annihilation processes, opening a new class of SIMP models with a local dark gauge symmetry. Depending on the mass difference between XI and XR, we have either two-component or three-component dark matter scenarios. In particular two- or three-component SIMP scenarios can be realised not only for small mass difference between X and Y, but also for large mass hierarchy between them, which is a new and unique feature of the present model. We consider both theoretical and experimental constraints, and present four case studies of the multi-component dark matter scenarios.

Strongly-interacting massive particle and dark photon in the era of the intensity frontier

A strongly interacting massive particle (SIMP) is an interesting candidate for dark matter (DM) because its self-interaction cross section can be naturally strong enough to address the astrophysical problem of small-scale structure formation. A simple model was proposed by assuming a monopole condensation, where composite SIMP comes from a "strongly interacting" U(1)$_{\rm d}$ gauge theory. In the original model, the DM relic abundance is determined by the $3\to2$ annihilation process via the Wess-Zumino-Witten term. In this letter, we discuss that the DM relic abundance is naturally determined also by a semi-annihilation process via a kinetic mixing between the hypercharge gauge boson and the dark U(1)$_{\rm d}$ gauge boson (dark photon). The dark photon can be discovered by LDMX-style missing momentum experiments in the near future.

Split SIMPs with decays

We discuss a minimal realization of the strongly interacting massive particle (SIMP) framework. The model includes a dark copy of QCD with three colors and three light flavors. A massive dark photon, kinetically mixed with the Standard Model hypercharge, maintains kinetic equilibrium between the dark and visible sectors. One of the dark mesons is necessarily unstable but long-lived, with potential impact on CMB observables. We show that an approximate “isospin” symmetry acting on the down-type quarks is an essential ingredient of the model. This symmetry stabilizes the dark matter and allows to split sufficiently the masses of the other states to suppress strongly their relic abundances. We discuss for the first time the SIMP cosmology with sizable mass splittings between all meson multiplets. We demonstrate that the SIMP mechanism remains efficient in setting the dark matter relic density, while CMB constraints on unstable relics can be robustly avoided. We also consider the phenomenological consequences of isospin breaking, including dark matter decay. Cosmological, astrophysical, and terrestrial probes are combined into a global picture of the parameter space. In addition, we outline an ultraviolet completion in the context of neutral naturalness, where confinement at the GeV scale is generic. We emphasize the general applicability of several novel features of the SIMP mechanism that we discuss here.

SIMPler realisation of scalar dark matter

With growing agony of not finding a dark matter (DM) particle in direct search experiments so far (for example in XENON1T), frameworks where the freeze-out of DM is driven by number changing processes within the dark sector itself and do not contribute to direct search, like Strongly Interacting Massive Particle (SIMP) are gaining more attention. In this analysis, we ideate a simple scalar DM framework stabilised by \U0001d4b53 symmetry to serve with a SIMP-like DM (χ) with additional light scalar mediation (ϕ) to enhance DM self interaction. We identify that a large parameter space for such DM is available from correct relic density and self interaction constraints coming from Bullet or Abell cluster data. We derive an approximate analytic solution for freeze-out of the SIMP like DM in Boltzmann equation describing 3DM → 2DM number changing process within the dark sector. We also provide a comparative analysis of the SIMP like solution with the Weakly Interacting Massive Particle (WIMP) realisation of the same model framework here.

Phenomenology of self-interacting dark matter in a matter-dominated universe

We study production of self-interacting dark matter (DM) during an early matter-dominated phase. As a benchmark scenario, we consider a model where the DM consists of singlet scalar particles coupled to the visible Standard Model (SM) sector via the Higgs portal. We consider scenarios where the initial DM abundance is set by either the usual thermal freeze-out or an alternative freeze-in mechanism, where DM was never in thermal equilibrium with the SM sector. For the first time, we take the effect of self-interactions within the hidden sector into account in determining the DM abundance, reminiscent to the Strongly Interacting Massive Particle (SIMP) scenario. In all cases, the number density of DM may change considerably compared to the standard radiation-dominated case, having important observational and experimental ramifications.

Twin Higgs model with strongly interacting massive particle dark matter

The hierarchy problem and the identity of dark matter are two of the central driving forces in particle physics. Twin Higgs models provide an elegant solution to the little hierarchy problem, while Strongly Interacting Massive Particles (SIMPs) provide an appealing dark matter candidate. Here we show that SIMPs can easily be embedded in the Twin Higgs setup, such that dark matter and the hierarchy problem can be addressed in a single framework. This also provides a natural explanation to the proximity between the confinement scale of SIMP dark matter and the strong scale of QCD.

Earth scattering of superheavy dark matter: Updated constraints from detectors old and new

Direct searches for Dark Matter (DM) are continuously improving, probing down to lower and lower DM-nucleon interaction cross sections. For strongly-interacting massive particle (SIMP) Dark Matter, however, the accessible cross section is bounded from above due to the stopping effect of the atmosphere, Earth and detector shielding. We present a careful calculation of the SIMP signal rate, focusing on super-heavy DM ($m_\chi \gtrsim 10^5 \,\,\mathrm{GeV}$) for which the standard nuclear-stopping formalism is applicable, and provide code for implementing this calculation numerically. With recent results from the low-threshold CRESST 2017 surface run, we improve the maximum cross section reach of direct detection searches by a factor of around 5000, for DM masses up to $10^8 \,\,\mathrm{GeV}$. A reanalysis of the longer-exposure, sub-surface CDMS-I results (published in 2002) improves the previous cross section reach by two orders of magnitude, for masses up to $10^{15} \,\,\mathrm{GeV}$. Along with complementary constraints from SIMP capture and annihilation in the Earth and Sun, these improved limits from direct nuclear scattering searches close a number of windows in the SIMP parameter space in the mass range $10^6$ GeV to $10^{13}$ GeV, of particular interest for heavy DM produced gravitationally at the end of inflation.

Phenomenology of ELDER dark matter

We explore the phenomenology of Elastically Decoupling Relic (ELDER) dark matter. ELDER is a thermal relic whose present density is determined primarily by the cross-section of its elastic scattering off Standard Model (SM) particles. Assuming that this scattering is mediated by a kinetically mixed dark photon, we argue that the ELDER scenario makes robust predictions for electron-recoil direct-detection experiments, as well as for dark photon searches. These predictions are independent of the details of interactions within the dark sector. Together with the closely related Strongly-Interacting Massive Particle (SIMP) scenario, the ELDER predictions provide a physically motivated, well-defined target region, which will be almost entirely accessible to the next generation of searches for sub-GeV dark matter and dark photons. We provide useful analytic approximations for various quantities of interest in the ELDER scenario, and discuss two simple renormalizable toy models which incorporate the required strong number-changing interactions among the ELDERs, as well as explicitly implement the coupling to electrons via the dark photon portal.

Axionlike particle assisted strongly interacting massive particle

We propose a new realization of strongly interacting massive particles (SIMP) as self-interacting dark matter, where SIMPs couple to the Standard Model sector through an axion-like particle. Our model gets over major obstacles accompanying the original SIMP model, such as a missing mechanism of kinetically equilibrating SIMPs with the SM plasma as well as marginal perturbativity of the chiral Lagrangian density. Remarkably, the parameter region realizing $\sigma_{\rm self}/m_{\rm DM} \simeq 0.1 \textrm{--} 1 \, {\rm cm}^{2}/{\rm g}$ is within the reach of future beam dump experiments such as the Search for Hidden Particles (SHiP) experiment.

Gravitational wave from dark sector with dark pion

In this work, we investigate the spectra of gravitational waves produced by chiral symmetry breaking in dark quantum chromodynamics (dQCD) sector. The dark pion (π) can be a dark matter candidate as weakly interacting massive particle (WIMP) or strongly interacting massive particle (SIMP). For a WIMP scenario, we introduce the dQCD sector coupled to the standard model (SM) sector with classical scale invariance and investigate the annihilation process of the dark pion via the 2π → 2 SM process. For a SIMP scenario, we investigate the 3π → 2π annihilation process of the dark pion as a SIMP using chiral perturbation theory. We find that in the WIMP scenario the gravitational wave background spectra can be observed by future space gravitational wave antennas. On the other hand, when the dark pion is the SIMP dark matter with the constraints for the chiral perturbative limit and pion-pion scattering cross section, the chiral phase transition becomes crossover and then the gravitational waves are not produced.

SIMP from a strong U(1) gauge theory with a monopole condensation

We provide a variant model of strongly interacting massive particle (SIMP), where composite dark matter comes from a strongly interacting U(1) theory. We first explain a non-Abelian version of the model with an additional singlet field, which is mixed with the Higgs field to maintain the kinetic equilibrium between the hidden and Standard Model (SM) sectors. The mixing leads to signals that would be detected by future collider experiments, direct DM detection experiments, and beam-dump experiments. Then we investigate a U(1) theory with a scalar monopole, where U(1) charged particles are confined by monopole condensation. In this model, the radial component of monopole can mix with the Higgs field, so that we do not need to introduce the additional singlet field.

SIMP model at NNLO in chiral perturbation theory

We investigate the phenomenological viability of a recently proposed class of composite dark matter models where the relic density is determined by 3 to 2 number-changing processes in the dark sector. Here the pions of the strongly interacting field theory constitute the dark matter particles. By performing a consistent next-to-leading and next-to-next-to-leading order chiral perturbative investigation we demonstrate that the leading order analysis cannot be used to draw conclusions about the viability of the model. We further show that higher order corrections substantially increase the tension with phenomenological constraints challenging the viability of the simplest realisation of the strongly interacting massive particle (SIMP) paradigm.

Astrophysical detection of heavy-particle-induced spectral shifts in muonic iron

By significantly increasing the nuclear mass, a strongly interacting massive particle (SIMP) bound to an iron nucleus would cause a characteristic change in the spectrum of muonic iron. At temperatures high enough that such atoms are completely stripped of electrons, the effect is directly observable as a $0.2%$ shift in the energies of high angular momentum states. This phenomenon provides a new test for the existence of SIMPs, which have been proposed as dark matter candidates, and as candidates for the lightest supersymmetric particle.

Search for anomalously heavy nuclei in gold and iron

There are a number of theoretical motivations for searching for anomalously heavy isotopes ${}_{Z}X$ of known elements, where Z is the nuclear charge of the anomalous nucleus X. Such nuclei could arise from the binding of a new strongly interacting massive particle (SIMP) to the nucleus of a known element, and could thus be detected as an anomalously heavy isotope of that element. SIMPs have been proposed as candidates for dark matter, and for the lightest supersymmetric particle, as well as a possible explanation for ultra high-energy cosmic rays. A search for anomalous nuclei X has been performed by analyzing several unique samples including gold nuggets collected in Australia, Arizona and North Carolina, gold foils flown on NASA's LDEF satellite, and an Fe meteorite. In each gold sample we scanned for Au isotopes with masses up to $1.67 \mathrm{TeV}{/c}^{2}$ using PRIME Lab, the Purdue accelerator mass spectrometer facility. We have also searched for anomalous Fe isotopes with masses up to $0.65 \mathrm{TeV}{/c}^{2}$ in the iron meteorite sample. We find no evidence for SIMPs in any of our samples, and our results set stringent limits on the abundance of anomalous isotopes of ordinary matter as a function of X mass.

Can the Strongly Interacting Dark Matter Be a Heating Source of Jupiter?

We show that the strongly·interacting massive particle (SIMP) with mass of 3x10 6 -10 7 GeV is astrophysically interesting as a dark matter candidate the galactic halo. The annihilation of SIMPs inside Jupiter naturally explains the intrinsic heat flux irrespective of details of the planetary models. We discuss its effect in all Jovian planets as well as in the Sun and the Earth. We also comment that such a SIMP is accommodated in a class of hadronic axion models. The dark matter (for a recent review, see, e.g., Ref. 1)) giving a large fraction of the gravitational mass of the galaxy may be composed of elementary particles. These particles must be so weakly-interacting or so few and heavy that they are not conspicuous. Many dark-matter candidates have been proposed!) and the possibil­ ities of their experimental detection have been intensively studied. 2 ) Among them the strongly-interacting dark-matters 3 ) are very interesting since they may allow the direct detection in the dark-matter search experiments on the Earth. In fact, only small regions have been left open for the strongly-interacting massive particles h (SIMPs), one with mass of 10 5 -10 7 GeV and the other with mass above 1010 GeV. 3 ) Furthermore, the recent experiment by Caldwell et a1. 4 ) has excluded some portion of the window. However the SIMP with mass of 3 X 10 6 -10 7 Ge V is still allowed. *) In this paper we point out that for the window, SIMPs are trapped in the planets and can annihilate in their centers producing possible heating energies. We indeed find that our model may explain the mysteriously large intrinsic heat flux of Jupiter 5 ) within the three standard deviations irrespective of the detailed parameters of the planet as well as the annihilation cross section. However for other Jovian planets,6),7) one must require that the SIMP's annihilation has not yet reached the steady state, since otherwise it overproduces the heating energy. In this case the predicted heat fluxes depend on details of the densities and temperatures of the planet cores and the annihilation cross section. We also examine SIMP's annihilation effects in the Earth and the Sun. The final comment is devoted to stressing that this stable SIMP is naturally accommodated in a class of hadronic axion models. Our basic assumption is that the dark halo of our galaxy 'is a cloud of the SIMPs h with the mass density Ph=OA GeV fcm