Dark Sector Research Articles

Constraints on the dark sector from electroweak precision observables

We revisit the standard model fit to electroweak precision observables (EWPO) using the latest data and the particle data group value of the mass of the W boson. This analysis is repeated for the value reported by CDF. The constraints on the parameter space for dark photons arising from these EWPO are then evaluated for both values of the W boson mass. We also extend previous work by placing the first electroweak precision observable constraints on the coupling of dark photons to the fermionic dark matter sector.

A closer look in the mirror: reflections on the matter/dark matter coincidence

We argue that the striking similarity between the cosmic abundances of baryons and dark matter, despite their very different astrophysical behavior, strongly motivates the scenario in which dark matter resides within a rich dark sector parallel in structure to that of the standard model. The near cosmic coincidence is then explained by an approximate ℤ2 exchange symmetry between the two sectors, where dark matter consists of stable dark neutrons, with matter and dark matter asymmetries arising via parallel WIMP baryogenesis mechanisms. Taking a top-down perspective, we point out that an adequate ℤ2 symmetry necessitates solving the electroweak hierarchy problem in each sector, without our committing to a specific implementation. A higher-dimensional realization in the far UV is presented, in which the hierarchical couplings of the two sectors and the requisite ℤ2-breaking structure arise naturally from extra-dimensional localization and gauge symmetries. We trace the cosmic history, paying attention to potential pitfalls not fully considered in previous literature. Residual ℤ2-breaking can very plausibly give rise to the asymmetric reheating of the two sectors, needed to keep the cosmological abundance of relativistic dark particles below tight bounds. We show that, despite the need to keep inter-sector couplings highly suppressed after asymmetric reheating, there can naturally be order-one couplings mediated by TeV scale particles which can allow experimental probes of the dark sector at high energy colliders. Massive mediators can also induce dark matter direct detection signals, but likely at or below the neutrino floor.

Singlet Dirac dark matter streamlined

We propose a new and compact realization of singlet Dirac dark matter within the WIMP framework. Our model replaces the standard Z 2 stabilizing symmetry with a Z 6, and uses spontaneous symmetry breaking to generate the dark matter mass, resulting in a much simplified scenario for Dirac dark matter. Concretely, we extend the Standard Model (SM) with just two new particles, a Dirac fermion (the dark matter) and a real scalar, both charged under the Z 6 symmetry. After acquiring a vacuum expectation value, the scalar gives mass to the dark matter and mixes with the Higgs boson, providing the link between the dark sector and the SM particles. With only four free parameters, this new model is extremely simple and predictive. We study the dark matter density as a function of the model's free parameters and use a likelihood approach to determine its viable parameter space. Our results demonstrate that the dark matter mass can be as large as 6 TeV while remaining consistent with all known theoretical and experimental bounds. In addition, a large fraction of viable models turns out to lie within the sensitivity of future direct detection experiments, furnishing a promising way to test this appealing scenario.

Leptogenesis, dark matter and gravitational waves from discrete symmetry breaking

We analyse a model that connects the neutrino sector and the dark sector of the universe via a mediator Φ, stabilised by a discrete 𝒵 4 symmetry that breaks to a remnant 𝒵 2 upon Φ acquiring a non-zero vacuum expectation value (vϕ ). The model accounts for the observed baryon asymmetry of the universe via additional contributions to the canonical Type-I leptogenesis. The 𝒵 4 symmetry breaking scale (vϕ ) in the model not only establishes a connection between the neutrino sector and the dark sector, but could also lead to gravitational wave signals that are within the reach of current and future experimental sensitivities.

Density dependent displaced vertex signatures as a novel probe of light dark sector scalars at the LHC

Dynamical theories of dark energy predict new degrees of freedom with particular environmental sensitivity to avoid constraints on fifth forces. We show that the similar, yet complementary multi-purpose detector setup of the ATLASand CMS experiments provides a unique opportunity to place sensitivity on such scenarios in a narrow, yet relevant parameter range. Furthermore, our investigation gives rise to a novel phenomenological signature that the LHC experimentscan pursue to exploit their complementary detector design from a BSM perspective.

Finsler–Randers–Sasaki gravity and cosmology

We present for the first time a Friedmann-like construction in the framework of an osculating Finsler–Randers–Sasaki (F–R–S) geometry. In particular, we consider a vector field in the metric on a Lorentz tangent bundle, and thus the curvatures of horizontal and vertical spaces, as well as the extra contributions of torsion and non-linear connection, provide an intrinsic richer geometrical structure, with additional degrees of freedom, that lead to extra terms in the field equations. Applying these modified field equations at a cosmological setup we extract the generalized Friedmann equations for the horizontal and vertical space, showing that we obtain an effective dark energy sector arising from the richer underlying structure of the tangent bundle. Additionally, as it is common in Finsler-like constructions, we obtain an effective interaction between matter and geometry. Finally, we consider a specific model and we show that it can describe the sequence of matter and dark-energy epochs, and that the dark-energy equation of state can lie in the quintessence or phantom regimes, or cross the phantom divide.

Asymmetric reheating via inverse symmetry breaking

Asymmetric reheating is a generic requirement for models of dark sectors with light species, but its implementation is usually in tension with unique phenomenologies otherwise possible in compelling theories containing dark copies of the Standard Model. We present a simple module to implement asymmetric reheating during a Z2-breaking phase above some critical temperature. This reinvigorates the possibility of an exactly degenerate mirror sector and the striking phenomenology of composite particles oscillating into their mirror counterparts. Published by the American Physical Society 2024

First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam

We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super Proton Synchrotron with a momentum of 160 GeV/c are directed to an active target. The signal signature consists of a single scattered muon with momentum <80 GeV/c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of (1.98±0.02)×1010 muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining (mZ′,gZ′) parameter space of a new Z′ (Lμ−Lτ) vector boson which could explain the muon (g−2)μ anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments. Published by the American Physical Society 2024

Careful Accounting Could Reveal the Dark Sector

Careful Accounting Could Reveal the Dark Sector

Coupled dark sector models and cosmological tensions

Coupled dark sector models and cosmological tensions

Unveiling Dark Forces with Measurements of the Large Scale Structure of the Universe.

Cosmology offers opportunities to test dark matter independently of its interactions with the standard model. We study the imprints of long-range forces acting solely in the dark sector on the distribution of galaxies, the so-called large scale structure (LSS). We derive the strongest constraint on such forces from a combination of Planck and BOSS data. Along the way we consistently develop, for the first time, the effective field theory of LSS in the presence of new dynamics in the dark sector. We forecast that future surveys will improve the current bound by an order of magnitude.

Collider signatures of near-continuum dark matter

In this paper we study a near-continuum dark matter model, in which dark sector consists of a tower of closely spaced states with weak-scale masses. We construct a five-dimensional model which naturally realizes this spectrum. The dark matter is described by a bulk field, which interacts with the brane-localized Standard Model sector via a Z portal. We then study collider signatures of this model. Near-continuum dark matter states produced in a collider undergo cascade decays, resulting in events with high multiplicity of jets and leptons, large missing energy, and displaced vertices. A custom-built Monte Carlo tool described in this paper allows for detailed simulation of the signal events. We present results of such simulations for the case of electron-positron collisions.

Probing the universe's expansion dynamics: The linear correction scenario perspective on dark energy

In this study, we investigate the cosmological evolution of the universe, focusing on the KMMS models in a model-independent approach, particularly the scenario involving linear correction, given by E2(z)=A(z)+β(1+γB(z)), where A(z)=Ωm0(1+z)3 and B(z)=z. By analyzing recent Cosmic Chronometers (CC) and the Pantheon+ samples, we determine the best-fit values of model parameters using a Markov chain Monte Carlo analysis. Our models exhibit unique dynamics, transitioning from super-exponential to exponential expansion, with a significant shift at redshift zt=0.83−0.10+0.11 and present deceleration parameter q0=−0.69−0.17+0.17. The jerk parameter exceeds 1, indicating a faster change in acceleration than predicted by ΛCDM. The energy density parameter is consistent with Planck observations, and the dark sector evolution follows the expected thermal history. The EoS parameter approaches ωde=−1 over time, with a current value of ωde0=−1.06±0.12, aligning with the phantom phase. Our model presents a new dark energy alternative, emphasizing the importance of considering models like KMMS in understanding cosmic evolution.

Perturbative reheating and thermalization of pure Yang-Mills plasma

We investigate the thermalization of high-energy particles injected from the perturbative decay of inflaton during the pre-thermal phase of reheating in detail. In general, thermalization takes a relatively long time in a low-temperature plasma; therefore, the instantaneous thermalization approximation is not justified, even for the reheating of the Standard Model (SM) sector. We consider a pure Yang-Mills (YM) theory as an approximation of the SM sector or a possible dark sector, considering the Landau-Pomeranchuk-Migdal effect, a quantum interference effect in a finite temperature plasma. We perform the first numerical calculation to solve the time evolution of the system, including the redshift due to the expansion of the Universe, and show the details of the temperature evolution near the maximum and the behavior of the quasi-attractors at later times. The maximal temperature Tmax and time scale tmax are determined quantitatively, such as Tmax ≃ 0.05 × ΓIMPI2/mI32/5mI\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\left({\\Gamma}_I{M}_{\ extrm{PI}}^2/{m}_I^3\\right)}^{2/5}{m}_I $$\\end{document} and tmax ≃ 2 × 103 × ΓIMPI2/mI3−3/5mI−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\left({\\Gamma}_I{M}_{\ extrm{PI}}^2/{m}_I^3\\right)}^{-3/5}{m}_I^{-1} $$\\end{document} in the SM-like system, where mI and ΓI are the mass and decay rate of inflaton. We also provide a similar formula for pure SU(N) and SO(N) YM theories for general values of N and coupling constant α, including Tmax ∝ α4/5 and tmax ∝ N−2α−16/5 behaviors and their numerical coefficients. The thermalization occurs in a finite time scale, resulting in a lower maximal temperature of the Universe after inflation than that under the instantaneous thermalization approximation.

Assessing the dark degeneracy through gas mass fraction data

It is well-known that Einstein’s equations constrain only the total energy–momentum tensor of the cosmic substratum, without specifying the characteristics of its individual constituents. Consequently, cosmological models featuring distinct decompositions within the dark sector, while sharing identical values for the sum of dark components’ energy–momentum tensor, remain indistinguishable when assessed through observables based on distance measurements. Notably, it has been already demonstrated that cosmological models with dynamical descriptions of dark energy, characterized by a time-dependent equation of state (EoS), can always be mapped into a model featuring a decaying vacuum (w=−1) coupled with dark matter. We explore the possibility of breaking this degeneracy by using measurements of the gas mass fraction observed in massive and relaxed galaxy clusters. This data is particularly interesting for this purpose because it isolates the matter contribution, possibly allowing the degeneracy breaking. We study the particular case of the wCDM model with its interactive counterpart. We compare the results obtained from both descriptions with a non-parametric analysis obtained through Gaussian Process. Even though the degeneracy may be broken from the theoretical point of view, we find that current gas mass fraction data seems to be insufficient for a final conclusion about which approach is favored, even when combined with SNIa, BAO and CMB.

Testing meson portal dark sector solutions to the MiniBooNE anomaly at the Coherent CAPTAIN Mills experiment

A solution to the MiniBooNE excess invoking rare three-body decays of the charged pions and kaons to new states in the MeV mass scale was recently proposed as a dark-sector explanation. This class of solution illuminates the fact that, while the charged pions were focused in the target-mode run, their decay products were isotropically suppressed in the beam-dump-mode run in which no excess was observed. This suggests a new physics solution correlated to the mesonic sector. We investigate an extended set of phenomenological models that can explain the MiniBooNE excess as a dark sector solution, utilizing long-lived particles that might be produced in the three-body decays of the charged mesons and the two-body anomalous decays of the neutral mesons. Over a broad set of interactions with the long-lived particles, we show that these scenarios can be compatible with constraints from LSND, KARMEN, and MicroBooNE, and evaluate the sensitivity of the ongoing and future data taken by the Coherent CAPTAIN Mills experiment to a potential discovery in this parameter space. Published by the American Physical Society 2024

Absorption of fermionic dark matter via the scalar portal

The absorption of fermionic dark matter has recently been studied as a signature for the direct detection of dark matter. We construct the first UV completion of the scalar effective operator associated with this signature. We calculate the constraints on the model and demonstrate there is viable parameter space which can be probed by a next-generation experiment such as XLZD. We also consider the cosmological history of our model and show that the correct relic abundance can be obtained via freeze-out in the dark sector. However, within this minimal model, we find that the absorption signal is highly suppressed in the parameter space that yields the correct relic abundance. Published by the American Physical Society 2024

The resurgence of the G(2) group for the strong sector and the emergence of dark matter

G(2) is the smallest exceptional group and it is the simplest and viable gauge group to minimally extend the strong interaction sector: G(2) includes the group SU(3) of Quantum Chromodynamics (QCD) as a maximal subgroup and it is equipped with six additional gluons that can acquire mass via a Higgs mechanism driven by a new Higgs particle and constitute dark matter. In this article I want to describe how the exceptional G(2) group can be a physical gauge group, capable of extending the Standard Model (SM) of particles and including a versatile dark sector, which is compatible with experimental observations. In fact, due to its peculiar mathematical features, the group G(2) manifests some complex features, not properly considered in literature, which guarantee its correct use in physics, as its {3}⊕{3‾} decompositions w.r.t. SU(3) can acquire a complex structure. The resulting framework can be a solid Beyond Standard Model (BSM) solution for the dark matter (DM) problem, in the form of massive complex scalar glueballs, and it includes the proper color representations for quarks and leptons. Several quantum field theory features are discussed, like the G(2) coupling constant running and its spectrum before and after the phase transition, along with all the DM astrophysical realizations, in order to present the unexpected potential of this gauge group.

Phases of Pseudo-Nambu-Goldstone bosons

We study the vacuum dynamics of pseudo-Nambu-Goldstone bosons (pNGBs) for SO(N + 1) → SO(N) spontaneous and explicit symmetry breaking. We determine the magnitude of explicit symmetry breaking consistent with an EFT description of the effective potential at zero and finite temperatures. We expose and clarify novel additional vacuum transitions that can arise for generic pNGBs below the initial scale of SO(N + 1) → SO(N) spontaneous symmetry breaking, which may have phenomenological relevance. In this respect, two phenomenological scenarios are analyzed: thermal and supercooled dark sector pNGBs. In the thermal scenario the vacuum transition is first-order but very weak. For a supercooled dark sector we find that, depending on the sign of the explicit symmetry breaking, one can have a symmetry-restoring vacuum transition SO(N – 1) → SO(N) which can be strongly first-order, with a detectable stochastic gravitational wave background signal.

CMB spectral distortions from an axion-dark photon-photon interaction

The presence of a plethora of light spin 0 and spin 1 fields is motivated in a number of BSM scenarios, such as the axiverse. The study of the interactions of such light bosonic fields with the Standard Model has focused mostly on interactions involving only one such field, such as the axion (ϕ) coupling to photons, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi F\\widetilde{F}$$\\end{document}, or the kinetic mixing between photon and the dark photon, FFD. In this work, we continue the exploration of interactions involving two light BSM fields and the standard model, focusing on the mixed axion-photon-dark-photon interaction \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi F{\\widetilde{F}}_{D}$$\\end{document}. If either the axion or dark photon are dark matter, we show that this interaction leads to conversion of the CMB photons into a dark sector particle, leading to a distortion in the CMB spectrum. We present the details of these unique distortion signatures and the resulting constraints on the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi F{\\widetilde{F}}_{D}$$\\end{document} coupling. In particular, we find that for a wide range of masses, the constraints from these effect are stronger than on the more widely studied axion-photon coupling.