arXiv subjects

Jan Heisig

Publications and source records attributed to Jan Heisig.

At least 37 records · Page 2Linked to original sources

arXiv2023

Dirac leptogenesis via scatterings

Leptogenesis typically requires the introduction of heavy particles whose out-of-equilibrium decays are essential for generating a matter-antimatter asymmetry, according to one of Sakharov's conditions. We show that in Dirac leptogenesis, scatterings between the light degrees of freedom - Standard Model particles plus Dirac neutrinos - suffice to generate the asymmetry. Sakharov's conditions are satisfied because the right-handed neutrino partners are out of equilibrium. Consequently, heavy degrees of freedom never needed to be produced in the early universe, allowing for a reheating temperature below their mass scale. We solve the Boltzmann equations and discuss the viable parameter space together with observational signatures such as an increased number of effective neutrinos in the early universe as well as proton decay for some realizations.

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arXiv2023

Testing Dirac leptogenesis with the cosmic microwave background and proton decay

The nature of neutrino masses and the matter-antimatter asymmetry of our universe are two of the most important open problems in particle physics today and are notoriously difficult to test with current technology. Dirac neutrinos offer a solution through a leptogenesis mechanism that hinges on the smallness of neutrino masses and resultant non-thermalization of the right-handed neutrino partners in the early universe. We thoroughly explore possible realizations of this Dirac leptogenesis idea, revealing new windows for highly efficient asymmetry generation. In many of them, the number of relativistic degrees of freedom, $N_\text{eff}$, is severely enhanced compared to standard cosmology and offers a novel handle to constrain Dirac leptogenesis with upcoming measurements of the cosmic microwave background. Realizations involving leptoquarks even allow for low-scale post-sphaleron baryogenesis and predict proton decay. These novel aspects render Dirac leptogenesis surprisingly testable.

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arXiv2023

Indirect dark-matter detection with MadDM v3.2 -- Lines and Loops

Automated tools for the computation of particle physics' processes have become the backbone of phenomenological studies beyond the standard model. Here, we present MadDM v3.2. This release enables the fully automated computation of loop-induced dark-matter annihilation processes, relevant for indirect detection observables. Special emphasis lies on the annihilation into $γX$, where $X=γ, Z, h$ or any new particle even under the dark symmetry. These processes lead to the sharp spectral feature of monochromatic gamma lines -- a smoking-gun signature of dark matter in our Galaxy. MadDM provides the predictions for the respective fluxes near-Earth and derives constraints from the gamma-ray line searches by Fermi-LAT and HESS. As an application, we discuss the implications for the viable parameter space of a top-philic $t$-channel mediator model and the inert doublet model.

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arXiv2023

Dark matter and radiative neutrino masses in conversion-driven scotogenesis

The scotogenic model generates Majorana neutrino masses radiatively, with dark matter particles running in the loop. We explore the parameter space in which the relic density of fermionic dark matter is generated via a conversion-driven freeze-out mechanism. The necessity for small Yukawa couplings to initiate chemical decoupling for conversion processes naturally reproduces small neutrino masses as long as the active neutrinos are hierarchical. The model can also resolve the recently reported deviation in the $W$-boson mass while satisfying constraints from direct detection, charged lepton flavor violation as well as collider bounds. Parts of the parameter space lead to long-lived particle signatures to be probed at the LHC.

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arXiv2022

Bound-state effects on dark matter coannihilation: Pushing the boundaries of conversion-driven freeze-out

Bound-state formation can have a large impact on the dynamics of dark matter freeze-out in the early Universe, in particular for colored coannihilators. We present a general formalism to include an arbitrary number of excited bound states in terms of an effective annihilation cross section, taking bound-state formation, decay and transitions into account, and derive analytic approximations in the limiting cases of no or efficient transitions. Furthermore, we provide explicit expressions for radiative bound-state formation rates for states with arbitrary principal and angular quantum numbers $n,\ell$ for a mediator in the fundamental representation of $SU(3)_c$, as well as electromagnetic transition rates among them in the Coulomb approximation. We then assess the impact of bound states within a model with Majorana dark matter and a colored scalar $t$-channel mediator. We consider the regime of coannihilation as well as conversion-driven freeze-out (or coscattering), where the relic abundance is set by the freeze-out of conversion processes. We find that the region in parameter space where the latter occurs is considerably enhanced into the multi-TeV regime. For conversion-driven freeze-out, dark matter is very weakly coupled, evading direct and indirect detection constraints but leading to prominent signatures of long-lived particles that provide great prospects to be probed by dedicated searches at the upcoming LHC runs.

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arXiv2022

Lyman-$α$ constraints on freeze-in and superWIMPs

Dark matter (DM) from freeze-in or superWIMP production is well known to imprint non-cold DM signatures on cosmological observables. We derive constraints from Lyman-$α$ forest observations for both cases, basing ourselves on a reinterpretation of the existing Lyman-$α$ limits on thermal warm DM. We exclude DM masses below 15 keV for freeze-in, in good agreement with previous literature, and provide a generic lower mass bound for superWIMPs that depends on the mother particle decay width. Special emphasis is placed on the mixed scenario, where contributions from both freeze-in and superWIMP are similarly important. In this case, the imprint on cosmological observables can deviate significantly from thermal warm DM. Furthermore, we provide a modified version of the Boltzmann code CLASS, analytic expressions for the DM distributions, and fits to the DM transfer functions that account for both mechanisms of production. Moreover, we also derive generic constraints from $ΔN_\mathrm{eff}$ measurements and show that they cannot compete with those arising from Lyman-$α$ observations. For illustration, we apply the above generic limits to a coloured $t$-channel mediator DM model, in which case contributions from both freeze-in through scatterings and decays, as well as superWIMP production can be important. We map out the entire cosmologically viable parameter space, cornered by bounds from Lyman-$α$ observations, the LHC, and Big Bang Nucleosynthesis.

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arXiv2022

Leptoquark manoeuvres in the dark: a simultaneous solution of the dark matter problem and the $R_{D^{(*)}}$ anomalies

The measured branching fractions of $B$-mesons into leptonic final states derived by the LHCb collaboration hint towards the breakdown of lepton flavour universality. In this work we take at face value the so-called $R_{D^{(*)}}$ observables that are defined as the ratios of neutral $B$-meson charged-current decays into a charged $D$-meson, a charged lepton and a neutrino final state in the tau and muon channels. A well-studied and simple solution to this charged current anomaly is to introduce a scalar leptoquark $S_1$ that couples to the second and third generation of fermions. We investigate how $S_1$ can also serve as a mediator between the Standard Model and a dark sector. We study this scenario in detail and estimate the constraints arising from collider searches for leptoquarks, collider searches for missing energy signals, direct detection experiments and the dark matter relic abundance. We stress that the production of a pair of leptoquarks that decays into different final states (i.e. the commonly called "mixed" channels) provides critical information for identifying the underlying dynamics, and we exemplify this by studying the $t τb ν$ and the resonant $S_1$ plus missing energy channels. We find that direct detection data provides non-negligible constraints on the leptoquark coupling to the dark sector, which in turn affects the relic abundance. We also show that the correct relic abundance can not only arise via standard freeze-out, but also through conversion-driven freeze-out. We illustrate the rich phenomenology of the model with a few selected benchmark points, providing a broad stroke of the interesting connection between lepton flavour violation and dark matter.

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arXiv2021

Cosmological imprints of non-thermalized dark matter

Non-thermalized dark matter is a cosmologically viable alternative to the widely studied weakly interacting massive particle. We study the evolution of the dark matter phase-space distributions arising from freeze-in and superWIMP production as well as the combination of both. Utilizing our implementation in CLASS, we investigate the cosmological imprints on the matter power spectrum, constrained by Lyman-$α$ forest observations. For the explicit example of a colored $t$-channel mediator model, we explore the cosmologically allowed parameter space highlighting the interplay of Lyman-$α$ constraints with those from Big Bang Nucleosynthesis and the LHC.

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arXiv2021

Constraining new physics with SModelS version 2

We present version 2 of SModelS, a program package for the fast reinterpretation of LHC searches for new physics on the basis of simplified model results. The major novelty of the SModelS v2 series is an extended topology description with a flexible number of particle attributes, such as spin, charge, decay width, etc. This enables, in particular, the treatment of a wide range of signatures with long-lived particles. Moreover, constraints from prompt and long-lived searches can be evaluated simultaneously in the same run. The current database includes results from searches for heavy stable charged particles, disappearing tracks, displaced jets and displaced leptons, in addition to a large number of prompt searches. The capabilities of the program are demonstrated by two physics applications: constraints on long-lived charged scalars in the scotogenic model, and constraints on the electroweak-ino sector in the Minimal Supersymmetric Standard Model.

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arXiv2021

Studying dark matter with MadDM: lines and loops

Automated tools for the computation of amplitudes and cross sections have become the backbone of phenomenological studies beyond the standard model. We present the latest developments in MadDM, a calculator of dark-matter observables based on MadGraph5_aMC@NLO. The new version enables the fully automated computation of loop-induced annihilation processes, relevant for indirect detection of dark matter. Of particular interest is the direct annihilation into photons, $γγ,\, γX$. These processes lead to monochromatic gamma-ray lines that are smoking-gun signatures for dark-matter annihilation in our Galaxy. MadDM computes the predictions for the expected photon fluxes near Earth and derives constraints from the gamma-ray line searches by Fermi-LAT and HESS. As an application, we present the implications for the parameter space of the Inert Doublet Model.

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arXiv2021

Revisiting the AMS-02 antiproton excess: The role of correlated errors

Cosmic-ray antiprotons are a remarkable diagnostic tool for the study of astroparticle physics' processes in our Galaxy. While the bulk of measured antiprotons is consistent with a secondary origin, several studies have found evidence for a subdominant primary component in the AMS-02 data. In this proceedings article, we revisit the excess considering systematic errors that could affect the signal. Of particular importance are unknown correlations in the AMS-02 systematic errors, the dominant of which are associated with the cross sections for cosmic-ray absorption in the detector. We compute their correlations in a careful reevaluation of nuclear scattering data, utilizing the Glauber-Gribov theory to introduce a welcomed redundancy that we explore in a global fit. The inclusion of correlated errors has a dramatic effect on the significance of the signal. In particular, the analysis becomes more sensitive to the diffusion model at low rigidities. For a minimal extension beyond single-power-law diffusion, the global significance drops below 1$σ$ severely questioning the robustness of the finding.

astro-ph.HE↗

arXiv2021

Cosmic-ray antiprotons in the AMS-02 era: A sensitive probe of dark matter

Cosmic-ray antiprotons are a powerful tool for astroparticle physics. While the bulk of measured antiprotons is consistent with a secondary origin, the precise data of the AMS-02 experiment provides us with encouraging prospects to search for a subdominant primary component, e.g. from dark matter. In this brief review, we discuss recent limits on heavy dark matter as well as a tentative signal from annihilation of dark matter with a mass $\lesssim 100$ GeV. We emphasize the special role of systematic errors that can affect the signal. In particular, we discuss recent progress in the modeling of secondary production cross sections and correlated errors in the AMS-02 data, the dominant ones originating from uncertainties in the cross sections for cosmic-ray absorption in the detector.

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arXiv2020

Studying dark matter with MadDM 3.1: a short user guide

MadDM is an automated numerical tool for the computation of dark-matter observables for generic new physics models. We announce version 3.1 and summarize its features. Notably, the code goes beyond the mere cross-section computation for direct and indirect detection. For instance, it allows the user to compute the fully differential nuclear recoil rates as well as the energy spectra of photons, neutrinos and charged cosmic rays for arbitrary $2\to n$ annihilation processes. This short user guide equips researchers with all the relevant information required to readily perform comprehensive phenomenological studies of particle dark-matter models.

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arXiv2020

New developments in SModelS

SModelS is an automatized tool enabling the fast interpretation of simplified model results from the LHC within any model of new physics respecting a $\mathbb{Z}_2$ symmetry. In this contribution, we report on two important updates of SModelS during 2020: the extension of the SModelS' database with 13 ATLAS and 10 CMS analyses, including 5 ATLAS and 1 CMS analyses at full Run~2 luminosity, and the ability to use full likelihoods now provided by ATLAS in the form of pyhf JSON files. Moreover, we briefly explain how to use SModelS and give an overview of ongoing developments.

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arXiv2020

Dark matter or correlated errors: Systematics of the AMS-02 antiproton excess

Several studies have pointed out an excess in the AMS-02 antiproton spectrum at rigidities of 10-20 GV. Its spectral properties were found to be consistent with a dark-matter particle of mass 50-100 GeV which annihilates hadronically at roughly the thermal rate. In this work, we reinvestigate the antiproton excess including all relevant sources of systematic errors. Most importantly, we perform a realistic estimate of the correlations in the AMS-02 systematic error which could potentially "fake" a dark-matter signal. The dominant systematics in the relevant rigidity range originate from uncertainties in the cross sections for absorption of cosmic rays within the detector material. For the first time, we calculate their correlations within the full Glauber-Gribov theory of inelastic scattering. The AMS-02 correlations enter our spectral search for dark matter in the form of covariance matrices which we make publicly available for the cosmic-ray community. We find that the global significance of the antiproton excess is reduced to below 1 $σ$ once all systematics, including the derived AMS-02 error correlations, are taken into account. No significant preference for a dark-matter signal in the AMS-02 antiproton data is found in the mass range 10-10000 GeV.

astro-ph.HE↗

arXiv2020

Reinterpretation of LHC Results for New Physics: Status and Recommendations after Run 2

We report on the status of efforts to improve the reinterpretation of searches and measurements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data.

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arXiv2020

New physics searches with heavy-ion collisions at the LHC

This document summarises proposed searches for new physics accessible in the heavy-ion mode at the CERN Large Hadron Collider (LHC), both through hadronic and ultraperipheral $γγ$ interactions, and that have a competitive or, even, unique discovery potential compared to standard proton-proton collision studies. Illustrative examples include searches for new particles -- such as axion-like pseudoscalars, radions, magnetic monopoles, new long-lived particles, dark photons, and sexaquarks as dark matter candidates -- as well as new interactions, such as non-linear or non-commutative QED extensions. We argue that such interesting possibilities constitute a well-justified scientific motivation, complementing standard quark-gluon-plasma physics studies, to continue running with ions at the LHC after the Run-4, i.e. beyond 2030, including light and intermediate-mass ion species, accumulating nucleon-nucleon integrated luminosities in the accessible fb$^{-1}$ range per month.

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arXiv2020

Global fit of pseudo-Nambu-Goldstone Dark Matter

We perform a global fit within the pseudo-Nambu-Goldstone dark matter (DM) model emerging from an additional complex scalar singlet with a softly broken global U(1) symmetry. Leading to a momentum-suppressed DM-nucleon cross section at tree level, the model provides a natural explanation for the null results from direct detection experiments. Our global fit combines constraints from perturbative unitarity, DM relic abundance, Higgs invisible decay, electroweak precision observables and latest Higgs searches at colliders. The results are presented in both frequentist and Bayesian statistical frameworks. Furthermore, post-processing our samples, we include the likelihood from gamma-ray observations of $\mathit{Fermi}$-LAT dwarf spheroidal galaxies and compute the one-loop DM-nucleon cross section. We find two favoured regions characterised by their dominant annihilation channel: the Higgs funnel and annihilation into Higgs pairs. Both are compatible with current $\mathit{Fermi}$-LAT observations, and furthermore, can fit the slight excess observed in four dwarfs in a mass range between about 30-300 GeV. While the former region is hard to probe experimentally, the latter can partly be tested by current observations of cosmic-ray antiprotons as well as future gamma-ray observations.

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