arXiv subjects

Leszek Roszkowski

Publications and source records attributed to Leszek Roszkowski.

At least 19 recordsLinked to original sources

arXiv2025

Dark photon dark matter from flattened axion potentials

Dark photons can be resonantly produced in the early universe via their coupling to an oscillating axion field. However, this mechanism typically requires large axion--dark photon couplings or some degree of fine-tuning. In this work, we present a new scenario in which efficient dark photon production arises from axion potentials that are shallower than quadratic at large field values. For moderately large initial misalignment angles, the oscillation of the axion field can trigger either efficient dark photon production or strong axion self-resonance via parametric resonance. When self-resonance dominates and disrupts the field's homogeneity, we show that oscillons -- localized, oscillating axion field configurations -- naturally form and can sustain continued dark photon production, provided the coupling is $\gtrsim \mathcal O(1)$. For dark photon mass up to three orders of magnitude below the axion mass, the produced dark photons can account for a significant fraction of the present-day dark matter. We support this scenario with numerical lattice simulations of a benchmark model. Our results further motivate experimental searches for ultralight dark photon dark matter. The simulation code is publicly available at https://github.com/hongyi18/AxionDarkPhotonSimulator.

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arXiv2025

Enhancing European Cooperation in the Search for Dark Matter

The search for dark matter is an exciting topic that is pursued in different communities over a wide range of masses and using a variety of experimental approaches. The result is a strongly correlated matrix of activities across Europe and beyond, both on the experimental and the theoretical side. We suggest to encourage and foster the collaboration of the involved institutions on technical, scientific and organisational level, in order to realise the synergies that are required to increase the impact of dark matter research and to cope with the increasing experiment sizes. The suggested network -- loosely titled "DMInfraNet" -- could be realised as a new initiative of the European strategy or be based on existing structures like iDMEu or DRD. The network can also serve as a nucleus for future joint funding proposals.

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arXiv2024

Revisiting signatures of thermal axions in nonstandard cosmologies

We revisit the formation of a thermal population of hadronic axions in nonstandard cosmologies, in light of the recent developments in obtaining continuous and smooth interaction rates for both the gluon and photon couplings. For certain cosmological histories, such as low-temperature reheating (LTR) and kination-like scenarios, the thermalization of the axion can be severely delayed to higher masses. In the case that thermal equilibrium is achieved, we improve the constraints on LTR for axion masses around the eV scale with respect to previous works and we constrain for the first time early matter-dominated (EMD) cosmologies. We also point out the possibility of having the co-existence of cold and warm dark matter populations of axions in kination-like scenarios in the eV mass range.

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arXiv2023

Indirect detection of long-lived particles in a rich dark sector with a dark vector portal

Simplified models of light new physics provide a convenient benchmark for experimental searches for new physics signatures, including dark matter (DM). However, additional detection modes can arise in less simplified and more realistic scenarios where new degrees of freedom are invoked. In this study, we introduce a non-minimal model based on a popular dark photon portal to DM where the mediator mass is obtained by interactions with the dark Higgs boson which acts as a long-lived particle. We further add to this scenario a new heavy DM species secluded from the Standard Model. In this model, which involves light and heavy particles in the dark sector, we find some new interesting phenomenological features that lead to complementary probes in intensity frontier searches for light long-lived particles, indirect detection searches for dark matter, and cosmic microwave background surveys. We also find possible non-local effects in the DM indirect detection searches that could significantly affect the usual detection strategies.

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arXiv2023

Extending preferred axion models via heavy-quark induced early matter domination

We examine the cosmological consequences of the heavy quarks in KSVZ-type axion models. We find that their presence often causes an early matter domination phase, altering the evolution of the Universe. This extends the axion mass into the region where standard cosmology leads to overproduction, and allows for a greater number of axion models with non-renormalizable terms to be viable. Quantitatively, we find that decays proceeding through effective terms of up to dimension 9 ($d=9$) remain consistent with cosmological constraints, in contrast with the result $d\leq5$ previously found in the literature. As a consequence, the heavy quarks can be much heavier and the axion mass window with the correct relic density for dark matter is extended by orders of magnitude, down to $m_a\approx 6\times 10^{-9} \,{\rm eV}$. This is achieved without resorting to fine-tuning of the initial misalignment angle, bolstering the motivation for many future axion haloscope experiments. Additionally, we explore how these models can be probed through measurements of the number of relativistic degrees of freedom at recombination.

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arXiv2023

Dark Matter Axions in the Early Universe with a Period of Increasing Temperature

We consider the production of axion dark matter through the misalignment mechanism in the context of a nonstandard cosmological history involving early matter domination by a scalar field with a time-dependent decay rate. In cases where the temperature of the Universe experiences a temporary period of increase, Hubble friction can be restored in the evolution of the axion field, resulting in the possibility of up to three "crossings" of the axion mass and the Hubble expansion rate. This has the effect of dynamically resetting the misalignment mechanism to a new initial state for a second distinct phase of oscillation. The resultant axion mass required for the present dark matter relic density is never bigger than the standard-history window and can be smaller by more than three orders of magnitude, which can be probed by upcoming experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN, targeting the axion-photon coupling. This highlights the possibility of exploring the cosmological history prior to Big Bang Nucleosynthesis through searches for axion dark matter beyond the standard window.

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arXiv2023

Dark matter production through a non-thermal flavon portal

The Froggatt-Nielsen (FN) mechanism provides an attractive way of generating the determined fermion mass hierarchy and quark mixing matrix elements in the Standard Model (SM). Here we extend it by coupling the FN field, the flavon, to a dark sector containing one or more dark matter particles which are produced non-thermally sequentially through flavon production. Non-thermal flavon production occurs efficiently via freeze-in and through field oscillations. We explore this in the regime of high-scale breaking $Λ$ of the global $U(1)_{\textrm{FN}}$ group and at the reheating temperature $T_R\ll Λ$ where the flavon remains out of equilibrium at all times. We identify phenomenologically acceptable regions of $T_R$ and the flavon mass where the relic abundance of dark matter and other cosmological constraints are satisfied. In the case of one-component dark matter we find an effective upper limit on the FN charges at high $Λ$, i.e. $Q_{\rm FN}^{\rm DM}\leq13$. In the multi-component dark sector scenario the dark matter can be the heaviest dark particle that can be effectively stable at cosmological timescales, alternatively it can be produced sequentially by decays of the heavier ones. For scenarios where dark decays occur at intermediate timescales, i.e. $t\sim 0.1- 10^{28}\,{\rm s}$, we find that existing searches can effectively probe interesting regions of parameter space. These searches include indirect probes on decays such as $γ$-ray and neutrino telescopes as well as analyses of the Cosmic Microwave Background, as well as constraints on small scale structure formation from the Lyman-$α$ forest. We comment on the future prospects of such probes, place projected sensitivities, and discuss how this scenario could accommodate the cosmological $S_8$ tension.

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arXiv2022

Simple and statistically sound recommendations for analysing physical theories

Physical theories that depend on many parameters or are tested against data from many different experiments pose unique challenges to statistical inference. Many models in particle physics, astrophysics and cosmology fall into one or both of these categories. These issues are often sidestepped with statistically unsound ad hoc methods, involving intersection of parameter intervals estimated by multiple experiments, and random or grid sampling of model parameters. Whilst these methods are easy to apply, they exhibit pathologies even in low-dimensional parameter spaces, and quickly become problematic to use and interpret in higher dimensions. In this article we give clear guidance for going beyond these procedures, suggesting where possible simple methods for performing statistically sound inference, and recommendations of readily-available software tools and standards that can assist in doing so. Our aim is to provide any physicists lacking comprehensive statistical training with recommendations for reaching correct scientific conclusions, with only a modest increase in analysis burden. Our examples can be reproduced with the code publicly available at https://doi.org/10.5281/zenodo.4322283.

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arXiv2021

New opportunities for axion dark matter searches in nonstandard cosmological models

We study axion dark matter production from a misalignment mechanism in scenarios featuring a general nonstandard cosmology. Before the onset of Big Bang nucleosynthesis, the energy density of the universe is dominated by a particle field $ϕ$ described by a general equation of state $ω$. The ensuing enhancement of the Hubble expansion rate decreases the temperature at which axions start to oscillate, opening this way the possibility for axions heavier than in the standard window. This is the case for kination, or in general for scenarios with $ω> 1/3$. However, if $ω< 1/3$, as in the case of an early matter domination, the decay of $ϕ$ injects additional entropy relative to the case of the standard model, diluting this way the preexisting axion abundance, and rendering lighter axions viable. For a misalignment angle $0.5 < θ_i < π/\sqrt{3}$, the usual axion window becomes expanded to $4 \times 10^{-9}$ eV $\lesssim m_a \lesssim 2 \times 10^{-5}$ eV for the case of an early matter domination, or to $2 \times 10^{-6}$ eV $\lesssim m_a \lesssim 10^{-2}$ eV for the case of kination. Interestingly, the coupling axion-photon in such a wider range can be probed with next generation experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN. Axion dark matter searches may therefore provide a unique tool to probe the history of the universe before Big Bang nucleosynthesis.

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arXiv2021

GUT-constrained supersymmetry and dark matter in light of the new $(g-2)_μ$ determination

The recent confirmation by the Fermilab-based Muon g-2 experiment of the $(g-2)_μ$ anomaly has important implications for allowed particle spectra in softly broken supersymmetry (SUSY) models with neutralino dark matter (DM). Generally, the DM has to be quite light, with the mass up to a few hundred GeV, and bino-dominated if it is to provide most of DM in the Universe. Otherwise, a higgsino or wino dominated DM is also allowed but only as a strongly subdominant component of at most a few percent of the total density. These general patterns can easily be found in the phenomenological models of SUSY but in GUT-constrained scenarios this proves much more challenging. In this paper we revisit the issue in the framework of some unified SUSY models with different GUT boundary conditions on the soft masses. We study the so-called non-universal gaugino model (NUGM) in which the mass of the gluino is disunified from those of the bino and the wino and an SO(10) and an SU(5) GUT-inspired models as examples. We find that in these unified frameworks the above two general patterns of DM can also be found, and thus the muon anomaly can also be accommodated, unlike in the simplest frameworks of the CMSSM or the NUHM. We show the resulting values of direct detection cross-section for points that do and do not satisfy the muon anomaly. On the other hand, it will be challenging to access those solutions at the LHC because the resulting spectra are generally very compressed.

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arXiv2021

Frozen-in fermionic singlet dark matter in non-standard cosmology with a decaying fluid

We perform a detailed study of dark matter production via freeze-in under the assumption that some fluid dominates the early Universe before depositing its energy to the plasma causing entropy injection. As a dark matter candidate we consider a fermionic singlet that is produced through its interactions with a scalar particle in the thermal plasma. The fluid alters the expansion rate of the Universe, as well as the scaling of the temperature, which significantly affects the evolution of both the number density and the mean momentum of the dark matter particle. We identify and discuss in detail the effects of the evolution of these quantities by considering several examples representing dark matter production at different stages of expansion and entropy injection. We find that, since the dark matter density is reduced when the entropy injection to the plasma continues after freeze-in, in order to reproduce its observational value an enhanced rate of dark matter production is required relative to standard cosmology. Furthermore, the impact of the assumed non-standard cosmological history on the dark matter mean momentum can result in either a relaxed or a tightened bound on the dark matter mass from large structure formation data.

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arXiv2021

Direct Detection of Dark Matter -- APPEC Committee Report

This Report provides an extensive review of the experimental programme of direct detection searches of particle dark matter. It focuses mostly on European efforts, both current and planned, but does it within a broader context of a worldwide activity in the field. It aims at identifying the virtues, opportunities and challenges associated with the different experimental approaches and search techniques. It presents scientific and technological synergies, both existing and emerging, with some other areas of particle physics, notably collider and neutrino programmes, and beyond. It addresses the issue of infrastructure in light of the growing needs and challenges of the different experimental searches. Finally, the Report makes a number of recommendations from the perspective of a long-term future of the field. They are introduced, along with some justification, in the opening Overview and Recommendations section and are next summarised at the end of the Report. Overall, we recommend that the direct search for dark matter particle interactions with a detector target should be given top priority in astroparticle physics, and in all particle physics, and beyond, as a positive measurement will provide the most unambiguous confirmation of the particle nature of dark matter in the Universe.

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arXiv2020

Extending the reach of FASER, MATHUSLA, and SHiP towards smaller lifetimes using secondary particle production

Many existing or proposed intensity-frontier search experiments look for decay signatures of light long-lived particles (LLPs), highly displaced from the interaction point, in a distant detector that is well-shielded from SM background. This approach is, however, limited to new particles with decay lengths similar to or larger than the baseline of those experiments. In this study, we discuss how this basic constraint can be overcome in BSM models that go beyond the simplest scenarios. If more than one light new particle is present in the model, an additional secondary production of LLPs may take place right in front of the detector, opening this way a new lifetime regime to be probed. We illustrate the prospects of such searches in the future experiments FASER, MATHUSLA and SHiP, for representative models, emphasizing possible connections to dark matter or an anomalous magnetic moment of muon. We also analyze additional advantages from employing dedicated neutrino detectors placed in front of the main decay volume.

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arXiv2020

Forbidden Freeze-In

We study the importance of a frozen-in dark matter production regime, where the dark matter particle is produced via kinematically forbidden decays that arise from significant thermal correction to the mass a mediator particle in the plasma.

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arXiv2020

Impact of uncertainties in the halo velocity profile on direct detection of sub-GeV dark matter

We use the state-of-the-art high-resolution cosmological simulations by IllustrisTNG to derive the velocity distribution and local density of dark matter in galaxies like our Milky Way and find a substantial spread in both quantities. Next we use our findings to examine the sensitivity to the dark matter velocity profile of underground searches using electron scattering in germanium and silicon targets. We find that sub-GeV dark matter search is strongly affected by these uncertainties, unlike nuclear recoil searches for heavier dark matter, especially in multiple electron-hole modes, for which the sensitivity to the scattering cross-section is also weaker. Therefore, by improving the sensitivity to lower ionization thresholds not only projected sensitivities will be boosted but also the dependence on the astrophysical uncertainties will become significantly reduced.

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arXiv2019

Forbidden frozen-in dark matter

We examine and point out the importance of a regime of dark matter production through the freeze-in mechanism that results from a large thermal correction to a decaying mediator particle mass from hot plasma in the early Universe. We show that mediator decays to dark matter that are kinematically forbidden at the usually considered ranges of low temperatures can be generically present at higher temperatures and actually dominate the overall dark matter production, thus leading to very distinct solutions from the standard case. We illustrate these features by considering a dark Higgs portal model where dark matter is produced via decays of a scalar field with a large thermal mass. We identify the resulting ranges of parameters that are consistent with the correct dark matter relic abundance and further apply current and expected future collider, cosmological, and astrophysical limits.

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arXiv2019

Testing dark matter with Cherenkov light -- prospects of H.E.S.S. and CTA for exploring minimal supersymmetry

We provide an updated and improved study of the prospects of the H.E.S.S. and Cherenkov Telescope Array (CTA) experiments in testing neutralino dark matter in the Minimal Supersymmetric Standard Model with nine free parameters (p9MSSM). We include all relevant experimental constraints and theoretical developments, in particular the calculation of the Sommerfeld enhancement for both present-day annihilation and the relic abundance. We perform a state-of-the-art analysis of the CTA sensitivity with a log-likelihood test ratio statistics and apply it to a numerical scan of the p9MSSM parameter space focusing on a TeV scale dark matter. We find that, assuming Einasto profile of dark matter halo in the Milky Way, H.E.S.S. has already been able to nearly reach the so-called thermal WIMP value, while CTA will go below it by providing a further improvement of at least an order of magnitude. Both H.E.S.S. and CTA are sensitive to several cases for which direct detection cross section will be below the so-called neutrino floor, with H.E.S.S. being sensitive to most of the wino region, while CTA also covering a large fraction of the ~1 TeV higgsino region. We show that CTA sensitivity will be further improved in the monochromatic photon search mode for both single-component and underabundant dark matter.

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arXiv2018

Flavor anomalies and dark matter in SUSY with an extra U(1)

Motivated by the recent anomalies in $b\rightarrow s$ transitions that emerged at LHCb, we consider a model with an $L_μ- L_τ$ gauge symmetry and additional vector-like fermions. We find that by introducing supersymmetry the model can be made consistent with the long-standing deviation in the measured value of the anomalous magnetic moment of the muon, $g-2$, and neutralino dark matter of broad mass ranges and properties. In particular, dark matter candidates include the well-known 1 TeV higgsino, which in the MSSM is typically not compatible with solutions to the $g-2$ puzzle. Moreover, its spin-independent cross section could be at the origin of the recent small excess in XENON-1T data. We apply to the model constraints arising from flavor precision measurements and direct searches at the Large Hadron Collider and show that they do not currently exclude the relevant parameter space regions.

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