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Journal articles on the topic 'Annihilation e⁺ e⁻'

Author: Grafiati

Published: 4 June 2021

Last updated: 18 February 2022

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1

Chan, Man Ho, and Chak Man Lee. "An excess radio signal in the Abell 4038 cluster." Monthly Notices of the Royal Astronomical Society 500, no. 4 (November 25, 2020): 5583–88. http://dx.doi.org/10.1093/mnras/staa2895.

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ABSTRACT In the past decade, various instruments, such as the Large Area Telescope (LAT) on the Fermi Gamma Ray Space Telescope, the Alpha Magnetic Spectrometer (AMS) and the Dark Matter Particle Explorer(DAMPE), have been used to detect the signals of annihilating dark matter in our Galaxy. Although some excesses of gamma rays, antiprotons and electrons/positrons have been reported and are claimed to be dark matter signals, the uncertainties of the contributions of Galactic pulsars are still too large to confirm the claims. In this paper, we report on a possible radio signal of annihilating dark matter manifested in the archival radio continuum spectral data of the Abell 4038 cluster. By assuming a thermal annihilation cross-section and comparing the dark matter annihilation model with the null hypothesis (cosmic ray emission without dark matter annihilation), we obtain very large test statistic (TS) values, TS > 45, for four popular annihilation channels, which correspond to more than 6σ statistical preference. This reveals a possible potential signal of annihilating dark matter. In particular, our results are also consistent with the recent claims of dark matter mass, m ≈ 30–50 GeV, annihilating via the $\rm b\bar{b}$ quark channel with the thermal annihilation cross-section. However, at this time, we cannot exclude the possibility that a better background cosmic ray model could explain the spectral data without recourse to dark matter annihilations.

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2

Chan, Man Ho, and Chak Man Lee. "A possible radio signal of annihilating dark matter in the Abell 4038 cluster." Monthly Notices of the Royal Astronomical Society: Letters 495, no. 1 (December 12, 2019): L124—L128. http://dx.doi.org/10.1093/mnrasl/slz185.

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ABSTRACT In the past decade, some telescopes [e.g. Fermi-Large Area Telescope (LAT), Alpha Magnetic Spectrometer(AMS), and Dark Matter Particle Explorer(DAMPE)] were launched to detect the signals of annihilating dark matter in our Galaxy. Although some excess of gamma-rays, antiprotons, and electrons/positrons have been reported and claimed as dark matter signals, the uncertainties of Galactic pulsars’ contributions are still too large to confirm the claims. In this Letter, we report a possible radio signal of annihilating dark matter manifested in the archival radio continuum spectral data of the Abell 4038 cluster. By assuming the thermal annihilation cross-section and comparing the dark matter annihilation model with the null hypothesis (cosmic ray emission without dark matter annihilation), we get very large test statistic values >45 for four popular annihilation channels, which correspond to more than 6.5σ statistical preference. This provides a very strong evidence for the existence of annihilating dark matter. In particular, our results also support the recent claims of dark matter mass m ≈ 30–50 GeV annihilating via the bb̄ quark channel with the thermal annihilation cross-section.

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3

Belotsky, K., M. Khlopov, and A. Kirillov. "Gamma-Ray Effects of Dark Forces in Dark Matter Clumps." Advances in High Energy Physics 2014 (2014): 1–6. http://dx.doi.org/10.1155/2014/651247.

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Existence of new gauge U(1) symmetry possessed by dark matter (DM) particles implies the existence of a new Coulomb-like interaction, which leads to Sommerfeld-Gamow-Sakharov enhancement of dark matter annihilation at low relative velocities. We discuss a possibility to put constraints on such dark forces of dark matter from the observational data on the gamma radiation in our Galaxy. Gamma-rays are supposed to originate from annihilation of DM particles in the small scale clumps, in which annihilation rate is supposed to be enhanced, besides higher density, due to smaller relative velocitiesvof DM particles. For possible cross sections, mass of annihilating particles, masses of clumps, and the contribution of annihilating particles in the total DM density we constrain the strength of new dark long range forces from comparison of predicted gamma-ray signal with Fermi/LAT data on unidentified point-like gamma-ray sources (PGS) as well as on diffuseγ-radiation. Both data on diffuse radiation and data on PGS put lower constraints on annihilation cross section at any dark interaction constant, where diffuse radiation provides stronger constraint at smaller clump mass. Density of annihilating DM particles is conventionally supposed to be defined by the frozen annihilation processes in early Universe.

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4

Gertsen, Anders S., Mads Koerstz, and Kurt V. Mikkelsen. "Benchmarking triplet–triplet annihilation photon upconversion schemes." Physical Chemistry Chemical Physics 20, no. 17 (2018): 12182–92. http://dx.doi.org/10.1039/c8cp00588e.

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5

Gajos, Aleksander. "Sensitivity of Discrete Symmetry Tests in the Positronium System with the J-PET Detector." Symmetry 12, no. 8 (August 1, 2020): 1268. http://dx.doi.org/10.3390/sym12081268.

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Study of certain angular correlations in the three-photon annihilations of the triplet state of positronium, the electron–positron bound state, may be used as a probe of potential CP and CPT-violating effects in the leptonic sector. We present the perspectives of CP and CPT tests using this process recorded with a novel detection system for photons in the positron annihilation energy range, the Jagiellonian Positron Emission Tomography (J-PET). We demonstrate the capability of this system to register three-photon annihilations with an unprecedented range of kinematical configurations and to measure the CPT-odd correlation between positronium spin and annihilation plane orientation with a precision improved by at least an order of magnitude with respect to present results. We also discuss the means to control and reduce detector asymmetries in order to allow J-PET to set the first measurement of the correlation between positronium spin and momentum of the most energetic annihilation photon which has never been studied to date.

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6

Lingenfelter, Richard E., and Reuven Ramaty. "Annihilation Radiation and Gamma-Ray Continuum from the Galactic Center Region." Symposium - International Astronomical Union 136 (1989): 587–605. http://dx.doi.org/10.1017/s0074180900187091.

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Observations of the time-dependent, electron-positron annihilation line radiation and gamma-ray continuum emission from the region of the Galactic Center show that there are two components to the annihilation line emission: a variable, compact source at or near the Galactic Center, and a steady, diffuse interstellar distribution. We suggest that the annihilating positrons in the compact source, observed from 1977 through 1979, result from photon-photon pair production, most likely around an accreting black hole, and that the annihilating, interstellar positrons result from the decay of radionuclei produced by thermonuclear burning in supernovae.

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7

Chajda, Ivan, and Helmut Länger. "Commutative rings whose ideal lattices are complemented." Asian-European Journal of Mathematics 12, no. 03 (May 27, 2019): 1950039. http://dx.doi.org/10.1142/s1793557119500396.

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We characterize those commutative rings [Formula: see text] whose ideal lattice [Formula: see text] endowed with the annihilation operation is an ortholattice. Moreover, we provide an analogous characterization for the annihilator lattice [Formula: see text] endowed with the annihilation operation. Since the ideal lattice of [Formula: see text] is modular, [Formula: see text] is already an orthomodular lattice provided it is an ortholattice. However, there exist also commutative rings whose ideal lattices are complemented but the complementation differs from annihilation. We present an example of such a ring and develop a procedure producing infinitely many rings with this property. Finally, we provide a sufficient condition for double annihilation to be a homomorphism from [Formula: see text] onto [Formula: see text].

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8

Durandin, Nikita A., Jussi Isokuortti, Alexander Efimov, Elina Vuorimaa-Laukkanen, Nikolai V. Tkachenko, and Timo Laaksonen. "Efficient photon upconversion at remarkably low annihilator concentrations in a liquid polymer matrix: when less is more." Chemical Communications 54, no. 99 (2018): 14029–32. http://dx.doi.org/10.1039/c8cc07592a.

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9

Stewart, A. T., C. V. Briscoe, and J. J. Steinbacher. "Positron annihilation in simple condensed gases." Canadian Journal of Physics 68, no. 12 (December 1, 1990): 1362–76. http://dx.doi.org/10.1139/p90-196.

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The angular-correlation technique of positron annihilation has been used to detect and measure the localized bubble state of positronium (Ps) in liquid Ne, Ar, Kr, H2, and N2 and in liquid and solid He at various pressures and temperatures. No bubble state was seen in liquid O2 or in solid Ne and Ar. The dynamics of bubble formation is not yet understood. In the cases where theoretical calculations, and adequate data, exist, viz. He, Ar, and H2, there is reasonable agreement for the momentum of the photons from the annihilation of positrons with the outer electrons of these atoms. The Ps annihilations from the self-trapped bubble state are reasonably well described in terms of a simple finite potential-well model.

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10

Chen, Shuoran, Fuming Chen, Pengju Han, Changqing Ye, Suqin Huang, Lei Xu, Xiaomei Wang, and Yanlin Song. "A stimuli responsive triplet–triplet annihilation upconversion system and its application as a ratiometric sensor for Fe3+ ions." RSC Advances 9, no. 62 (2019): 36410–15. http://dx.doi.org/10.1039/c9ra06524e.

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11

Salati, Pierre. "Dark matter annihilation in the universe." International Journal of Modern Physics: Conference Series 30 (January 2014): 1460256. http://dx.doi.org/10.1142/s2010194514602567.

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The astronomical dark matter is an essential component of the Universe and yet its nature is still unresolved. It could be made of neutral and massive elementary particles which are their own antimatter partners. These dark matter species undergo mutual annihilations whose effects are briefly reviewed in this article. Dark matter annihilation plays a key role at early times as it sets the relic abundance of the particles once they have decoupled from the primordial plasma. A weak annihilation cross section naturally leads to a cosmological abundance in agreement with observations. Dark matter species subsequently annihilate — or decay — during Big Bang nucleosynthesis and could play havoc with the light element abundances unless they offer a possible solution to the 7 Li problem. They could also reionize the intergalactic medium after recombination and leave visible imprints in the cosmic microwave background. But one of the most exciting aspects of the question lies in the possibility to indirectly detect the dark matter species through the rare antimatter particles — antiprotons, positrons and antideuterons — which they produce as they currently annihilate inside the galactic halo. Finally, the effects of dark matter annihilation on stars is discussed.

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12

Ye, Chen, Victor Gray, Khushbu Kushwaha, Sandeep Kumar Singh, Paul Erhart, and Karl Börjesson. "Optimizing photon upconversion by decoupling excimer formation and triplet triplet annihilation." Physical Chemistry Chemical Physics 22, no. 3 (2020): 1715–20. http://dx.doi.org/10.1039/c9cp06561j.

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Perylene is a common annihilator in triplet–triplet annihilation photon upconversion schemes. It has however a tendency for excimer formation, which can be reduced by mono-alkylation without severely compromising the TTA-UC efficiency.

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13

Lovas, I. "Annihilation." Materials Science Forum 105-110 (January 1992): 85–100. http://dx.doi.org/10.4028/www.scientific.net/msf.105-110.85.

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14

Luper-Foy, Steven. "Annihilation." Philosophical Quarterly 37, no. 148 (July 1987): 233. http://dx.doi.org/10.2307/2220396.

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15

Wilson, Reuel K., Piotr Szewc, and Ewa Hryniewicz-Yarbrough. "Annihilation." World Literature Today 68, no. 2 (1994): 397. http://dx.doi.org/10.2307/40150276.

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16

Choi, Soo-Min, Hyun Min Lee, and Min-Seok Seo. "SIMP dark matter and its cosmic abundances." EPJ Web of Conferences 168 (2018): 06009. http://dx.doi.org/10.1051/epjconf/201816806009.

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We give a review on the thermal average of the annihilation cross-sections for 3 → 2 and general higher-order processes. Thermal average of higher order annihilations highly depend on the velocity of dark matter, especially, for the case with resonance poles. We show such examples for scalar dark matter in gauged Z3 models.

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17

Zverev, Vladimir V., Mikhail N. Dubovik, and Boris N. Filippov. "3-D Simulations of Micromagnetic Transition Structures in Vortex Asymmetric Domain Walls." Solid State Phenomena 215 (April 2014): 421–26. http://dx.doi.org/10.4028/www.scientific.net/ssp.215.421.

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The three-dimensional transition structures in the vortex asymmetric domain walls existing in magnetically uniaxial soft magnetic films with in-plane anisotropy are studied by micromagnetic simulations. It is shown that interaction of closely spaced transition structures results in various dynamical scenarios including vortex-antivortex annihilations, creation and annihilation of singular (Bloch) points, and excitation of nonlinear waves.

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18

Chiba, M., J. Nakagawa, H. Tsugawa, R. Ogata, and T. Nishimura. "A detector with high detection efficiency in 4- and 5-photon-positronium annihilations." Canadian Journal of Physics 80, no. 11 (November 1, 2002): 1287–95. http://dx.doi.org/10.1139/p02-107.

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We first measured 4- and 5-photon annihilations in positronium using a multiphoton spectrometer (UNI), which consists of 32 NaI(Tl) scintillators with lead shields, each being located on a surface of an icosidodecahedron. The front face of each scintillator is placed at a distance of L = 262 mm from the center of the UNI. With this setup, the detection efficiency of 4- and 5-photon-annihilation processes are too small to get a sufficient number of events to analyze the physics. To obtain a larger detection efficiency, we must set the NaI(Tl) scintillators closer to the target. The original principle in designing the UNI was to suppress backgrounds (BG) and make them as low as possible allowing modest efficiencies for 4- and 5-photon-annihilation events, i.e., to get the highest signal-to-noise ratio (S/N). The new concept is to get the highest S/σ where σ is an error of one standard deviation of the signal including BG effects. A higher S/σ means a larger number of events with smaller BG taking into account a statistical effect. The detection efficiencies with BG effects are studied with respect to L using a detector simulator based on the EGS4 code in which 2- to 5-photon-annihilation events are generated by quantum-electrodynamic processes based on GRACE and BASES/SPRING codes. As a result, the detection efficiency and S/σ of 5-photon annihilations at L = 136 mm are 529 and 17 times larger than those at L = 262 mm, respectively. PACS Nos.: 36.10Dr, 12.20Fv, 13.10+q

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19

Ghosh, Dipak, Jaya Roy, and Ranjan Sengupta. "Scaling of the multiplicity distribution of target protons emitted in relativistic heavy-ion collisions and antiproton annihilation in nuclei." Canadian Journal of Physics 64, no. 11 (November 1, 1986): 1509–11. http://dx.doi.org/10.1139/p86-267.

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This paper reports the observation of Koba–Neilsen–Olesen-type scaling in the multiplicity distribution of medium-energy protons emitted in relativistic heavy-ion interactions and antiproton [Formula: see text] annihilations in nuclei. The data have been taken from 12C–AgBr (emulsion) interactions at 4.5 GeV∙c−1∙nucleon−1 and [Formula: see text] annihilation in emulsions at 1.4 GeV∙c−1

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20

Lynn, K. G., Bent Nielsen, and D. O. Welch. "Hydrogen interaction with oxidized Si(111) probed with positrons." Canadian Journal of Physics 67, no. 8 (August 1, 1989): 818–20. http://dx.doi.org/10.1139/p89-141.

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A variable-energy positron beam was utilized to study the interface action of hydrogen with Si(111) covered by an ultrahigh-vacuum thermally grown oxide of 2–3 nm thickness. It was observed that positrons implanted at shallow depth (<100 nm) after diffusion are trapped either at the interface between the oxide and the Si or in the oxide. The positron-annihilation characteristics of these trapped positrons are found to be very sensitive to hydrogen exposure. The momentum distribution of the annihilating positron–electron pair, as observed in the Doppler broadening of the annihilation line, broadens considerably after exposure to hydrogen. The effect recovers after annealing at [Formula: see text], suggesting a hydrogen binding at the interface of ~3 ± 0.3 eV.

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21

Panther, Fiona H., Roland M. Crocker, Ivo R. Seitenzahl, and Ashley J. Ruiter. "SN1991bg-like supernovae are a compelling source of most Galactic antimatter." Proceedings of the International Astronomical Union 11, S322 (July 2016): 176–79. http://dx.doi.org/10.1017/s1743921316011911.

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AbstractThe Milky Way Galaxy glows with the soft gamma ray emission resulting from the annihilation of ~5 × 1043 electron-positron pairs every second. The origin of this vast quantity of antimatter and the peculiar morphology of the 511keV gamma ray line resulting from this annihilation have been the subject of debate for almost half a century. Most obvious positron sources are associated with star forming regions and cannot explain the rate of positron annihilation in the Galactic bulge, which last saw star formation some 10 Gyr ago, or else violate stringent constraints on the positron injection energy. Radioactive decay of elements formed in core collapse supernovae (CCSNe) and normal Type Ia supernovae (SNe Ia) could supply positrons matching the injection energy constraints but the distribution of such potential sources does not replicate the required morphology. We show that a single class of peculiar thermonuclear supernova - SN1991bg-like supernovae (SNe 91bg) - can supply the number and distribution of positrons we see annihilating in the Galaxy through the decay of 44Ti synthesised in these events. Such 44Ti production simultaneously addresses the observed abundance of 44Ca, the 44Ti decay product, in solar system material.

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22

Matsumoto, Hajime, Eiichi Sukedai, and Hatsujiro Hashimoto. "Annihilation Behaviors of Athermal ω-Phase Crystals Due to Electron Irradiation." Microscopy and Microanalysis 6, no. 4 (July 2000): 362–67. http://dx.doi.org/10.1007/s100050010031.

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Abstract Annihilation behaviors of athermal ω-phase crystals formed by cooling at 131 K for 10.8 ks under four different electron irradiation conditions of acceleration voltages of 200 kV and 160 kV, and beam currents of approximately 20 pA/cm2 and 5 pA/cm2 were investigated using in situ dark field and HREM observation methods at 131 K. The effect of acceleration voltages on the lifetimes is recognized, i.e., in the case of approximately equal electron beam current, lifetimes at 200 kV become shorter than those at 160 kV. Also, lifetimes depend on the electron beam current at 200 kV, i.e., the higher the beam currents, the shorter the lifetimes become. However, no distinct dependence can be seen at 160 kV. Since annihilations of athermal ω-phase crystals begin after the electron irradiation for a certain period in each condition, which depends on acceleration voltages and beam currents, it is suggested that the annihilation behaviors have incubation periods.

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23

Burley, Mikel. "Anticipating Annihilation." Inquiry 49, no. 2 (April 2006): 170–85. http://dx.doi.org/10.1080/00201740600576993.

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24

Toms, Derek. "Instant annihilation." New Scientist 201, no. 2696 (February 2009): 25. http://dx.doi.org/10.1016/s0262-4079(09)60518-2.

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25

Klein, Dennis. "Micro-annihilation." Historical Reflections/Reflexions Historiques 39, no. 2 (January 1, 2013): 1–6. http://dx.doi.org/10.3167/hrrh.2013.390201.

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26

Harbour, C. "Potential annihilation." British Dental Journal 203, no. 2 (July 2007): 63. http://dx.doi.org/10.1038/bdj.2007.649.

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27

Gusterson, Hugh. "Inventing Annihilation." Social Studies of Science 36, no. 4 (August 2006): 634–40. http://dx.doi.org/10.1177/0306312706064813.

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28

Dalrymple, Theodore. "Contemplating annihilation." BMJ 334, no. 7586 (January 25, 2007): 211.1–211. http://dx.doi.org/10.1136/bmj.39101.510023.b7.

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29

Lerner, R. B. "Donne's Annihilation." Journal of Medieval and Early Modern Studies 44, no. 2 (April 1, 2014): 407–27. http://dx.doi.org/10.1215/10829636-2647346.

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30

Henke, Kim, and Janice Eigsti. "Self-annihilation." Dimensions of Critical Care Nursing 24, no. 3 (May 2005): 117–19. http://dx.doi.org/10.1097/00003465-200505000-00003.

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31

Chan, Man. "Radio Constraints of Dark Matter: A Review and Some Future Perspectives." Galaxies 9, no. 1 (January 28, 2021): 11. http://dx.doi.org/10.3390/galaxies9010011.

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In the past few decades, many studies have analyzed the data of gamma-rays, X-rays, radio waves, electrons, positrons, anti-protons, and neutrinos to search for the signal of dark matter annihilation. In particular, analyzing radio data has been one of the most important and effective ways to constrain dark matter. In this article, we review the physics and the theoretical framework of using radio data to constrain annihilating dark matter. We also review some important radio constraints of annihilating dark matter and discuss the future perspectives of using radio detection to reveal the nature of dark matter.

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32

Kira, Ibrahim A., Thomas Templin, Linda Lewandowski, Vidya Ramaswamy, Bulent Ozkan, Jamal Mohanesh, and Abdulkhaleq Hussam. "Collective and Personal Annihilation Anxiety: Measuring Annihilation Anxiety AA." Psychology 03, no. 01 (2012): 90–99. http://dx.doi.org/10.4236/psych.2012.31015.

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33

Aghai-Khozani, H., M. Corradini, R. Hayano, M. Hori, M. Leali, E. Lodi-Rizzini, V. Mascagna, et al. "Experimental technique for antiproton-nucleus annihilation cross section measurements at low energy." EPJ Web of Conferences 182 (2018): 03009. http://dx.doi.org/10.1051/epjconf/201818203009.

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The interaction of very low energy antiprotons (ps) and antineutrons (ns) with nuclei is interesting for its influence on both fundamental cosmology and nuclear physics. Measuring the annihilation cross section of antimatter on matter can help in solving the universe matter-antimatter puzzle and could give relevant hints in the definition of strong interaction model parameters as well. The ASACUSA collaboration recently measured the antiproton-carbon annihilation cross section at 5.3 MeV of kinetic energy of the incoming antiproton. The experimental apparatus consisted in a vacuum chamber containing thin foils (~0.7-1 μm) of carbon crossed by a bunched beam of antiprotons from the CERN Antiproton Decelerator (AD). The fraction of antiprotons annihilating on the target nucleons gives origin to charged pions which can be detected and counted by segmented scintillators placed outside the chamber. This work describes the experimental details of the apparatus and the technique to perform the cross section measurements.

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34

Belyanin, A. A., V. V. Kocharovskii, and Vl V. Kocharovskii. "Collective Electron-Positron Annihilation." International Astronomical Union Colloquium 128 (1992): 117–22. http://dx.doi.org/10.1017/s0002731600154903.

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AbstractThe phenomenon of collective spontaneous annihilation of a magnetized electron-positron plasma is predicted. Like the superradiance in systems with discrete energy spectra, collective annihilation leads to the generation of powerful coherent radiation with the rate of this process considerably exceeding the spontaneous annihilation and collisional relaxation rates.

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35

Zhang, Yan Hui, Dong Wang, Chang Shu He, Xing Zhong Cao, and Lin Zhang. "Effect of Heat Treatment on Positron Annihilation Lifetime of an Extruded Al-12.7Si-0.7Mg Alloy." Materials Science Forum 788 (April 2014): 258–61. http://dx.doi.org/10.4028/www.scientific.net/msf.788.258.

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Positron annihilation lifetime can reflect the information of electronic density. Therefore this technique is very sensitive to the vacancies. Therefore positron annihilation technology (PAT) is a non-destructive testing technology for the investigation on the vacancy in pure metals and alloys. The vacancy defects of as-cast pure aluminium and the extruded Al-12.7Si-0.7Mg alloy before and after heat treatment were investigated by positron annihilation lifetime spectra. The results of positron annihilation lifetime spectra show that the lifetime of free positron annihilation in the pure aluminium alloy is 155 ps. The positron annihilation lifetime of the extruded sample is longer than the lifetime in the pure aluminium due to the formation of grain boundary and dislocation during the extrusion process. The positron annihilation lifetime of the extruded sample after heat treatment is shorter than that before the heat treatment, and it is longer than that of the pure sample.

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36

ANCHISHKIN, D., and R. NARYSHKIN. "PION AND QUARK ANNIHILATION MECHANISMS OF DILEPTON PRODUCTION IN RELATIVISTIC HEAVY ION COLLISIONS." Modern Physics Letters A 20, no. 27 (September 7, 2005): 2047–55. http://dx.doi.org/10.1142/s0217732305018311.

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The medium-induced modifications of the π+π- and [Formula: see text] annihilation mechanisms of dilepton production during relativistic heavy-ion collisions are considered in the frame of a specific model. The main assumption of the model: the pions (quarks) produced during a collision are effectively confined to a finite volume due to the dense hadron environment, in which they live for a finite time scaled as the lifetime of a fireball. The effect of the contraction of the phase space of the annihilating pion (quark) states on dilepton spectra is analyzed.

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37

Murgia, Simona. "The Fermi–LAT Galactic Center Excess: Evidence of Annihilating Dark Matter?" Annual Review of Nuclear and Particle Science 70, no. 1 (October 19, 2020): 455–83. http://dx.doi.org/10.1146/annurev-nucl-101916-123029.

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The center of the Galaxy is one of the prime targets in the search for a signal of annihilating (or decaying) dark matter. If such a signal were to be detected, it would shed light on one of the biggest mysteries in physics today: What is dark matter? Fundamental properties of the particle nature of dark matter, such as its mass, annihilation cross section, and annihilation final states, could be measured for the first time. Several experiments have searched for such a signal, and some have measured excesses that are compatible with it. A long-standing and compelling excess is observed in γ-rays by the Fermi Large Area Telescope ( Fermi–LAT). This excess is consistent with a dark matter particle with a mass of approximately 50 (up to ∼200) GeV annihilating with a velocity-averaged cross section of ∼10−26 cm3 s−1. Although a dark matter origin of the excess remains viable, other interpretations are possible. In particular, there is some evidence that the excess is produced by a population of unresolved point sources of γ-rays—for example, millisecond pulsars. In this article, I review the current status of the observation of the Fermi–LAT Galactic center excess, the possible interpretations of the excess, the evidence and counterevidence for each, and the prospects for resolving its origin with future measurements.

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38

Waithe, Mary Ellen. "Adoration and Annihilation." International Philosophical Quarterly 50, no. 4 (2010): 501–8. http://dx.doi.org/10.5840/ipq201050436.

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39

Rosenbaum, Stephen. "Epicurus and Annihilation." Philosophical Quarterly 39, no. 154 (January 1989): 81. http://dx.doi.org/10.2307/2220353.

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40

Dempsey, Liam, and Byron Stoyles. "Comfort in Annihilation." Forum Philosophicum 15, no. 1 (2010): 119–40. http://dx.doi.org/10.5840/forphil201015121.

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41

Smith, Gerald A. "Antiproton annihilation spectra." Hyperfine Interactions 44, no. 1-4 (March 1989): 43–57. http://dx.doi.org/10.1007/bf02398656.

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42

Botta, E. "Antineutron–nucleus annihilation." Nuclear Physics A 692, no. 1-2 (September 2001): 39–46. http://dx.doi.org/10.1016/s0375-9474(01)01157-5.

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Tretyak, V. I. "Study of annihilation." Nuclear Physics A 692, no. 1-2 (September 2001): 379–82. http://dx.doi.org/10.1016/s0375-9474(01)01203-9.

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OUGIZAWA, Toshiaki. "Positron Annihilation Spectroscopy." Kobunshi 55, no. 9 (2006): 750–54. http://dx.doi.org/10.1295/kobunshi.55.750.

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OUGIZAWA, Toshiaki, and Makoto MURAMATSU. "Positron Annihilation SPectroscoPy." Kobunshi 51, no. 10 (2002): 831. http://dx.doi.org/10.1295/kobunshi.51.831.

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Hillis, Raymond E. "Psyche and annihilation." Psychological Perspectives 16, no. 1 (March 1985): 51–73. http://dx.doi.org/10.1080/00322928508407943.

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Maity, Tarak Nath, and Tirtha Sankar Ray. "Resonant assisted annihilation." Journal of Cosmology and Astroparticle Physics 2019, no. 11 (November 26, 2019): 033. http://dx.doi.org/10.1088/1475-7516/2019/11/033.

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Forward, Robert. "Antiproton annihilation propulsion." Journal of Propulsion and Power 1, no. 5 (September 1985): 370–74. http://dx.doi.org/10.2514/3.22811.

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Jean, Y. C., X. Lu, Y. Lou, A. Bharathi, C. S. Sundar, Y. Lyu, P. H. Hor, and C. W. Chu. "Positron annihilation inC60." Physical Review B 45, no. 20 (May 15, 1992): 12126–29. http://dx.doi.org/10.1103/physrevb.45.12126.

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Weise, W. "Antinucleon - nucleon annihilation." Nuclear Physics A 558 (June 1993): 219–33. http://dx.doi.org/10.1016/0375-9474(93)90396-f.

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