Direct Annihilation Research Articles

Minimal mass of thermal dark matter and the viability of millicharged particles affecting 21-cm cosmology

Thermal freeze-out offers an attractive explanation of the dark matter density free from fine-tuning of initial conditions. For dark matter with a mass below tens of MeV, photons, electrons, and neutrinos are the only available direct Standard Model annihilation products. Using a full three-sector abundance calculation, we determine the minimal mass of dark matter, allowing for an arbitrary branching into electrons/photons and neutrinos that is compatible with current cosmological observations. The analysis takes into account the heat transfer between the various sectors from annihilation elastic scattering, representing the first fully self-consistent analysis that tracks the respective sectors’ temperatures. We thereby provide accurate thermal annihilation cross sections, particularly for velocity-dependent cases, and deduce the sensitivity of current and upcoming CMB experiments to MeV thermal dark matter. In the latter context, we also establish the fine-tuned parameter region where a tiny admixture of neutrinos in the final states rules in MeV-scale p-wave annihilating DM into electrons. Finally, we show that a sub-% millicharged dark matter with an interaction strength that interferes with 21-cm cosmology is still allowed when freeze-out is supplemented with annihilation into neutrinos. For all cases considered, we provide concrete particle physics models and supplement our findings with a discussion of other relevant experimental results. Published by the American Physical Society 2024

Rare species of dark matter

I discuss implications of rare species of particles that have larger than commonly assumed interaction and/or annihilation cross sections. Large fractions of the parameter space of such models remain unexplored. I point out a number of the most interesting consequences, such as large accumulation of such particles in the earth, direct annihilation inside large neutrino detectors, possibility to accelerate such particles using particle beams with subsequent detection using the direct detection experiments. I also discuss the de-excitations on nuclear isomers through a recoil on dark matter, as well as in-situ formation of the DM-nucleus bound states.

Hint for a Minimal Interaction Length in e+e−⟶γγ Annihilation in Total Cross Section of Center-of-Mass Energies 55-207 GeV

The measurements of the total cross section of the e+e−⟶γγγ reaction from the VENUS, TOPAS, OPAL, DELPHI, ALEPH, and L3 collaborations, collected between 1989 and 2003, are used to perform a χ2 test to validate the current quantum electrodynamics (QED) theory and search for possible deviations with the direct contact term annihilation. By observing a deviation from the QED predictions on the total cross section of the e+e−⟶γγγ reaction above s=180.0 GeV, a non-QED direct contact term is introduced following the dimension 6 effective theory to explain the deviation. In the non-QED direct contact term, a threshold energy scale Λ is included and explained to the finite interaction length in direct contact term and in consequence the size of the electron involved in the annihilation area. The experimental data of the total cross section is compared to the QED cross section by a χ2 test, which gives a best fit of the Λ to be 1576±202 GeV, corresponding to a finite interaction length of re=1.25±0.16×10−17 (cm). In the direct contact term annihilation, this interaction length is a measure of the size of an electron re. By combining all the data results from the mentioned collaborations, we have at least 2 to 3 times more statistics than every single experiment at high s region. This induces the best precision on re compared to the previous measurements.

Fuel-Driven Enzymatic Reaction Networks to Program Autonomous Thiol/Disulfide Redox Systems.

Fuel-driven dissipative formation of disulfide bonds using competing oxidative activation and reductive deactivation presents a possibly very versatile avenue for autonomous materials design. However, this is challenging to realize because of the direct annihilation of oxidizing fuel and a deactivating reducing agent. We overcome this challenge by introducing a redox-based enzymatic reaction network (ERN), enabling the dissipative disulfide formation for molecularly dissolved thiols in a fully autonomous manner. Moreover, the ERN allows for programming hydrogel lifetimes by utilizing thiol-terminated star polymers (sPEG-SH). The ERN can be customized to operate with aliphatic and aromatic thiols and should thus be broadly applicable to functional thiols.

The physics case for neutrino–neutrino collisions

Addressing the mass origin and properties of neutrinos is of strong interest to particle physics, baryogenesis and cosmology. Popular explanations involve physics beyond the standard model, for example, the dimension-5 Weinberg operator or heavy Majorana neutrinos arising from ‘seesaw’ models. The current best direct limits on the electron neutrino mass, derived from nuclei beta decay or neutrinoless double beta decay processes, are at the sub-electronvolt level. Here we propose a novel neutrino–neutrino collider where the neutrino beam is generated from TeV scale muon decays. Such collisions can happen between either neutrinos and anti-neutrinos, or neutrinos and neutrinos. We find that with a tiny integrated luminosity of about 10−5 fb−1 we can already expect to observe direct neutrino anti-neutrino annihilation, νν¯→Z , which also opens the door to explore neutrino related resonances νν¯→X . The low luminosity requirement can accommodate a relatively large emittance muon beam. Such a device would also allow for probing heavy Majorana neutrino and effective Majorana neutrino mass through ν ν → HH to a competitive level, for both electron and muon types.

The quintuplet annihilation spectrum

We extend the Effective Field Theory of Heavy Dark Matter to arbitrary odd representations of SU(2) and incorporate the effects of bound states. This formalism is then deployed to compute the gamma-ray spectrum for a 5 of SU(2): quintuplet dark matter. Except at isolated values of the quintuplet mass, the bound state contribution to hard photons with energy near the dark-matter mass is at the level of a few percent compared to that from direct annihilation. Further, compared to smaller representations, such as the triplet wino, the quintuplet can exhibit a strong variation in the shape of the spectrum as a function of mass. Using our results, we forecast the fate of the thermal quintuplet, which has a mass of ~13.6 TeV. We find that existing H.E.S.S. data should be able to significantly test the scenario, however, the final word on this canonical model of minimal dark matter will likely be left to the Cherenkov Telescope Array (CTA).

Advanced Molecular Design for Efficient Multicolor Electrochemiluminescence and Amplified Spontaneous Emission Based on Tetra‐BF2 Complexes

AbstractAdvanced organoboron dyes, incorporating tetra‐boron difluoride (tetra‐BF2) moieties, are developed, demonstrating efficient electrochemiluminescence (ECL) emissions in the green to orange regions through direct ion annihilation. By introducing diverse alkyl modifications in the molecules, luminescence color tuning is achieved via alterations in conjugation and bending angle. A photoluminescence quantum yield of 100% in dilute solutions is successfully achieved. Notably, the introduction of alkyl groups to the methine side stabilizes the radical ionic state, resulting in a high ECL efficiency of 74% through an efficient radical‐ion annihilation pathway. The key factor is that the energy of the annihilation reaction exceeds the S1 energy required for luminescence. Spin density calculations further elucidate the substituent effects on the radical ions of complexes. Moreover, the lasing properties of these materials in the solution‐processed blend films are investigated, revealing a low amplified spontaneous emission (ASE) threshold (Eth) of 6.40 ± 0.24 µJ cm−2, which is notably lower among organic laser materials. This is attributed to their large Stokes shifts and high quantum yield. The excellent ECL and ASE performances establish these materials as a valuable addition to the existing library of organoboron dyes, offering fresh insights into the development of organic solid‐state lasers.

A Monte Carlo strategy to simulate positrons and positronium in biological materials

We present an algorithm for Monte Carlo simulations of positron tracks in biological materials. The algorithm takes into account the cross-section data for elastic and inelastic collisions between positrons and molecules and processes like direct annihilation, ionization and positronium formation. In the case of positronium formation, the algorithm considers the interactions of positronium with molecules. The algorithm can be used to identify the processes that are responsible to determine the lifetime of the positrons and their annihilation mechanism (direct or through positronium formation).

Cyborgs vs. Vatniks: Hybridity, Weaponized Information, and Mediatized Reality in Recent Ukrainian War Films

Abstract Focusing on Akhtem Seitablaiev’s blockbuster Kiborhy: Heroi ne vmyraiut (Cyborgs: Heroes Never Die, 2017) and Sergei Loznitsa’s auteur production Donbass (2018), this article argues that the 2014–2022 cycle of Ukrainian war films merits critical attention as an astute record of conspicuous social transformations in pre-full-scale-invasion Ukraine and for their original perspective on the hybrid nature of modern war and its mediatization. The article uses postcolonial and cyborg theories of hybridity, Baudrillard’s concept of simulacra, and the Marxist notion of “false consciousness” to illustrate how post-Soviet, postcolonial, and post-truth aspects of war-torn Ukraine conflate in Seitablaiev’s and Loznitsa’s works to highlight the recent shift in the nature of warfare itself. As the two films unequivocally demonstrate, the latter is defined not so much by high-tech armed operations and direct annihilation of the opponent as by contactless warfare, as well as by its consequences for those directly influenced by it.

Annihilation-gamma-based diagnostic techniques for magnetically confined electron–positron pair plasma

Efforts are underway to magnetically confine electron–positron pair plasmas to study their unique behaviour, which is characterized by significant changes in plasma time and length scales, supported waves and unstable modes. However, use of conventional plasma diagnostics presents challenges with these low-density and annihilating matter–antimatter plasmas. To address this problem, we propose to develop techniques based on the distinct emission provided by annihilation. This emission exhibits two spatial correlations: the distance attenuation of isotropic sources and the back-to-back propagation of momentum-preserving 2 $\gamma$ annihilation. We present the results of our analysis of the $\gamma$ emission rate and the spatial profile of the annihilation in a magnetized pair plasma from direct pair collisions, from the formation and decay of positronium as well as from transport processes. In order to demonstrate the effectiveness of annihilation-based techniques, we tested them on annular $\gamma$ emission profiles produced by a $\beta ^+$ radioisotope on a rotating turntable. Direct and positronium-mediated annihilation result in overlapping volumetric $\gamma$ sources, and the 2 $\gamma$ emission from these volumetric sources can be tomographically reconstructed from coincident counts in multiple detectors. Transport processes result in localized annihilation where field lines intersect walls, limiters or internal magnets. These localized sources can be identified by the fractional $\gamma$ counts on spatially distributed detectors.

Searching for heavy neutral lepton and lepton number violation through VBS at high-energy muon colliders

High-energy muon collider can play as an emitter of electroweak gauge bosons and thus leads to substantial vector boson scattering (VBS) processes. In this work, we investigate the production of heavy neutral lepton (HNL) N and lepton number violation (LNV) signature through VBS at high-energy muon colliders. VBS induces LNV processes W±Z/γ → ℓ±N → ℓ±ℓ±W∓ → ℓ±ℓ±qq¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ q\\overline{q} $$\\end{document}′ with an on-shell HNL N at μ+μ− colliders. In analogy to neutrinoless double-beta decay with the HNL in t-channel, the LNV signature W+W+ → ℓ+ℓ+ can also happen via VBS at same-sign muon collider. They provide clean and robust LNV signatures to tell the nature of Majorana HNLs and thus have more advantageous benefits than direct μμ annihilation. We analyze the potential of searching for Majorana HNL and obtain the exclusion limits on mixing VℓN. Based on this same-sign lepton signature, we also obtain the sensitivity of muon collider to the Weinberg operator.

Enhanced cosmic-ray antihelium production from dark matter annihilation through light mediators

Cosmic-ray (CR) antihelium is an important probe for the indirect search of dark matter (DM) annihilation in the Galaxy. However, due to stringent constraints from the measurements of CR antiprotons and γ-rays, the flux of CR antihelium from the conventional DM direct annihilation into Standard Model final states is expected to be far below the sensitivity of the current experiments. We show that the production of antihelium can be significantly enhanced if the DM particles annihilate through light mediator particles with a mass mϕ ≈ 8 GeV close to the antihelium production threshold. After taking into account the constraints from the AMS-02 antiproton data and the Fermi-LAT γ-ray data on the spheroidal dwarf galaxies, we find that in this scenario the CR antihelium flux can be enhanced by three orders of magnitude, which makes it within the sensitivity of the ongoing AMS-02 experiment.

Nucleon Electromagnetic Form Factors Measurements at BESIII

Electromagnetic form factors provide fundamental information to reveal the internal structure and dynamincs of nucleons. Using the energy scan data collected by BESIII experiment on BEPCII collider, the Born cross section of e+e−→pp¯ and e+e−→nn¯, and the proton and neutron electromagnetic form factors are measured at center-of-mass energies between 2.0 and 3.08 GeV, through the e+e− direct annihilation process. Through the initial-state-radiation process, the proton electromagnetic form factors are also measured from the pp¯ threshold to 3.0 GeV with the large data sets collected at center-of-mass energy between 3.773 and 4.6 GeV, while the Born cross section of e+e−→pp¯ is measured up to 3.8 GeV.

Cyborgs vs. Vatniks: Hybridity, Weaponized Information, and Mediatized Reality in Recent Ukrainian War Films

Focusing on Akhtem Seitablaiev’s blockbuster Kiborhy: Heroi ne vmyraiut' (Cyborgs: Heroes Never Die, 2017) and Sergei Loznitsa’s auteur production Donbass (2018), this article argues that the latest cycle of Ukrainian war films merits critical attention as an astute record of conspicuous social transformations in today’s Ukraine and as a medium that presents an original perspective on the hybrid nature of modern war and its mediatization, the latter being a relatively new theme in war films broadly defined. The article uses post-colonial and cyborg theories of hybridity, Baudrillard’s concept of simulacra, and the Marxist notion of “false consciousness” to illustrate how post-Soviet, post-colonial, and post-truth aspects of war-torn Ukraine conflate in Seitablaev’s and Loznitsa’s works to bring to the fore a recent shift in the nature of warfare itself. As the two films unequivocally demonstrate, the latter is defined not so much by high-tech armed operations and direct annihilation of the opponent as by contactless warfare, as well as its consequences for those directly influenced by it.

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.

Study on pure annihilation type B→Vγ decays

We investigate the pure annihilation type radiative $B$ meson decays $B^0 \to \phi \gamma$ and $B_s \to \rho^0(\omega)\gamma$ in the soft-collinear effective theory. We consider three types of contributions to the decay amplitudes, including the direct annihilation topology, the contribution from the electro-magnetic penguin operator and the contribution of the neutral vector meson mixings. The numerical analysis shows that the decay amplitudes are dominated by the $\omega-\phi$ mixing effect in the $B^0 \to \phi\gamma$ and $B_s \to \omega\gamma$ modes. The corresponding decay branching ratios are enhanced about three orders of magnitudes relative to the pure annihilation type contribution in these two decay channels. The decay rate of $B_s \to \rho^0\gamma$ is much smaller than that of $B_s \to \omega\gamma$ because of the smaller $\rho^0-\phi$ mixing. The predicted branching ratios $B(B^{0}\rightarrow\phi\gamma)=(3.99^{+1.67}_{-1.46} )\times10^{-9},\,B(B_s\rightarrow\omega\gamma)=(2.01^{+0.81}_{-0.71} )\times10^{-7}$ are to be tested by the Belle-II and LHC-b experiments.

Direct Annihilation Position Classification Based on Deep Learning Using Paired Cherenkov Detectors: A Monte Carlo Study

To apply deep learning to estimate the three-dimensional interaction position of a Cherenkov detector, an experimental measurement of the true depth of interaction is needed. This requires significant time and effort. Therefore, in this study, we propose a direct annihilation position classification method based on deep learning using paired Cherenkov detectors. The proposed method does not explicitly estimate the interaction position or time-of-flight information and instead directly estimates the annihilation position from the raw data of photon information measured by paired Cherenkov detectors. We validated the feasibility of the proposed method using Monte Carlo simulation data of point sources. A total of 125 point sources were arranged three-dimensionally with 5 mm intervals, and two Cherenkov detectors were placed face-to-face, 50 mm apart. The Cherenkov detector consisted of a monolithic PbF2 crystal with a size of 40 × 40 × 10 mm3 and a photodetector with a single photon time resolution (SPTR) of 0 to 100 picosecond (ps) and readout pitch of 0 to 10 mm. The proposed method obtained a classification accuracy of 80% and spatial resolution with a root mean square error of less than 1.5 mm when the SPTR was 10 ps and the readout pitch was 3 mm.

Estimating relationship between the time over threshold and energy loss by photons in plastic scintillators used in the J-PET scanner

PurposeThe time-over-threshold (TOT) technique is being used widely due to itsimplications in developing the multi-channel readouts, mainly when fast signal processing is required. Using the TOT technique, as a measure of energy loss instead of charge integration methods, significantly reduces the signal readout costs by combining the time and energy information. Therefore, this approach can potentially be utilized in J-PET tomograph which is built from plastic scintillators characterized by fast light signals. The drawback in adopting this technique lies in the non-linear correlation between input energy loss and TOT of the signal. The main motivation behind this work is to develop the relationship between TOT and energy loss and validate it by the J-PET tomograph setup.MethodsThe experiment was performed using a 22Na beta emitter source placed in the center of the J-PET tomograph. This isotope produces photons of two different energies: 511 keV photons from the positron annihilation (direct annihilation or through the formation of a para-positronium atom or pick-off process of ortho-positronium atoms) and a 1275 keV prompt photon. This allows the study of the correlation between TOT values and energy loss for energy ranges up to 1000 keV. Since the photon interacts predominantly via Compton scattering inside the plastic scintillator, there is no direct information of the energy deposition. However, using the J-PET geometry, one can measure the scattering angle of the interacting photon. Since the 22Na source emits photons of two different energies, it is necessary to know unambiguously the energy of incident photons and their corresponding scattering angles in order to estimate energy deposition. In summary, this work presents a dedicated algorithm developed to tag photons of different energies and studying their scattering angles to calculate the energy deposition by the interacting photons.ResultsA new method was elaborated to measure the energy loss by photons interacting with plastic scintillators used in the J-PET tomograph. We find the relationship between the energy loss and TOT is non-linear and can be described by the functions TOT = A0 + A1 * ln(E dep + A2) + A3 * (ln(E dep + A2))2 and TOT = A0 - A1 * A2^{E_{dep}}phantom {dot {i}!}. In addition, we also introduced a theoretical model to calculate the TOT as a function of energy loss in plastic scintillators.ConclusionsA relationship between TOT and energy loss by photons interacting inside the plastic scintillators used in J-PET scanner is established for a deposited energy range of 100–1000 keV.

Understanding the atomistic deformation mechanisms of polycrystalline γ-TiAl under nanoindentation: Effect of lamellar structure

Molecular dynamics (MD) simulations have been performed to study the deformation behavior of polycrystalline γ-TiAl under nanoindentation. Effect of three different lamellar structure patterns is investigated respectively. Simulation results reveal that the lamellar samples are soft due to a dislocation-nucleation-controlled softening mechanism. Dislocations propagate along lamellar interface and experience no obstacle. Moreover, not only grain boundary (GB) but also lamellar interfaces can act as sliding interfaces, the additional sliding interface can also assist softening of lamellar samples. In addition, the different evolution processes of the three γ/γ interface variants are also investigated. Lamellar coarsening can be observed in the true-twin (TT) sample due to the direct migration and annihilation of TT interfaces. While the pseudo-twin (PT) and rotational-boundary (RB) interfaces cannot migrate directly but transform to each other at the origin interface planes, thus the origin lamellar spacing remains.

Some implications of the leptonic annihilation of dark matter: possible galactic radio emission signatures and the excess radio flux of extragalactic origin

We give theoretical predictions for the radio emission of a dark matter candidate annihilating into 2-lepton and 4-lepton final states. We then compare our results with the known radio measurements of the sky temperature as a function of the frequency. In particular, we calculate the radio emission for some dark matter candidates annihilating into intermediate bosons that subsequently decay into a 4-lepton channel with a thermal annihilation cross-section. We show that within the range of frequencies from 20 MHz to 5 GHz, this channel can produce a stronger signature than direct annihilation into leptons.