Antistars in the Galaxy
A. D. Dolgov

Novosibirsk State University, Novosibirsk, Russia

20th Lomonosov Conference on Elementary Particle Physics
Moscow State University (Moscow, Russia)
19 - 25 August, 2021
Supported by the RSF Grant 20-42-09010

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Content

1

Conventional baryogenesis

2

CP violation in cosmology and possible antimatter domain

3

Possible discovery of antistars in the Galaxy.

4

Antistar dark matter.

5

A model of abundant antistar creation in galaxies.

6Conclusion

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Conventional baryogenesis
A.D. Sakharov, three principles:• Nonconservation of baryonic number.
• C and CP (explicit) violation.
• Deviation from thermal equilibrium.
”Cosmological constant”:
β = NB /Nγ = const
In simple versions of the scenario antibaryons are not created by theSakharov mechanism.
Baryogenesis could proceed without any one of the Sakharov’sconditions.

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C and CP violation in cosmology
Antimatter creation depends upon the way of charge symmetry violation:• 1. Explicit.
• 2. Spontaneous.
• 3. Dynamical.
Explicit is achieved by complex coupling constants or masses.
Spontaneous - by spontaneous symmetry breaking when a complex scalar
field acquires non-zero vacuum expectation value. The universe consists ofmatter and antimatter domain separated by walls which are to beeliminated.
Dynamical one is realized if a classical complex scalar field is somehow
realized in the early universe e.g. due to quantum instability of masslessfields at de Sitter stage (inflation), but this field disappears later leaving
no trace. No domain wall problem. Regions with different values and signsof β can be created.
In versions 2 and 3 antistars are formed but far away from stars, indifferent galaxies.
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Discovery of antistars?

S. Dupourqué, L. Tibaldo, P. Von Ballmoos, Phys.Rev.D 103 (2021) 8,083016 • e-Print: 2103.10073 [astro-ph.HE] Possible discovery of several
antistars in the Galaxy was recently reported: ”Constraints on theantistar fraction in the Solar System neighborhood from the 10-year Fermi
Large Area Telescope gamma-ray source catalog.” S. Dupourqué, L.
Tibaldo, P. Von Ballmoos, Phys.Rev.D 103 (2021) 8, 083016 • e-Print:
2103.10073 [astro-ph.HE] ”We identify in the catalog 14 antistar
candidates not associated with any objects belonging to establishedgamma-ray source classes and with a spectrum compatible withbaryon-antibaryon annihilation.”A. D. Dolgov

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Dark antimatterIn a recent publication a striking idea was put forward that dark matter
may consist of compact anti-stars: J. S. Sidhu, R.J. Scherrer, G.
Starkman, ”Antimatter as Macroscopic Dark Matter”, arXiv:2006.01200,
astro-ph.CO. Such anti-DM may be easier to spot than other forms ofmacroscopic DM.

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Antistar prediction

Existence of antistars in the Galaxy was predicted many years ago.
Mechanism of massive PBH formation with log-normal mass spectrum:
A. Dolgov and J.Silk, PRD 47 (1993) 4244 ”Baryon isocurvaturefluctuations at small scale and baryonic dark matter.
A.Dolgov, M. Kawasaki, N. Kevlishvili, Nucl.Phys. B807 (2009) 229,
”Inhomogeneous baryogenesis, cosmic antimatter, and dark matter”.
Massive PBHs allow to cure multpie inconsistencies with the standard
cosmology and astrophysics. Unusual stellar type compact objects arealso created, including abundant antistars in the Galaxy.
An evidence in favor of the mechanism: The chirp mass distributionof LIGO events very well agrees with theoretical predictions, AD, A.G.
Kuranov, N.A. Mitichkin, S. Porey, K.A. Postnov, et al JCAP 12 (2020)
017 - a strong support of the scenario.

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Bounds on antistars in the Galaxy
As argued in:
C. Bambi, A.D. Dolgov, ”Antimatter in the Milky Way”, Nucl.Phys.B
784 (2007) 132-150 • e-Print: astro-ph/0702350,
A.D. Dolgov, S.I. Blinnikov, ”Stars and Black Holes from the very
Early Universe”, Phys.Rev.D 89 (2014) 2, 021301 • e-Print: 1309.3395,
S.I. Blinnikov, A.D. Dolgov, K.A. Postnov, ”Antimatter and antistars inthe universe and in the Galaxy”, Phys.Rev.D 92 (2015) 2, 023516 •e-print: 1409.5736
an abundant density of compact anti-stars in the universe and even in theGalaxy does not violate existing observational limits. Such anti-DM may
be easier to spot than other forms of macroscopic DM.
Surface annihilation on a compact object is much less efficient thanvolume annihilation, e.g. inside gas cloud of antimatter.

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Antimatter creation by mirror matter

Antistars or antimatter cores in mirror neutron stars? Zurab Berezhiani(Jun 21, 2021) e-Print: 2106.11203 [astro-ph.HE]
The oscillation of the neutron n into mirror neutron n0 , its partner fromdark mirror sector, can gradually transform an ordinary neutron star into amixed star consisting in part of mirror dark matter. The implications of
the reverse process taking place in the mirror neutron stars depend on thesign of baryon asymmetry in mirror sector. Namely, if it is negative, aspredicted by certain baryogenesis scenarios, then n̄0 − n̄ transitions createa core of our antimatter gravitationally trapped in the mirror star interior.

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Anti-Creation Mechanism

The mechanism of massive PBH and antistar formation:
A. Dolgov and J.Silk, PRD 47 (1993) 4244 ”Baryon isocurvaturefluctuations at small scale and baryonic dark matter.
A.Dolgov, M. Kawasaki, N. Kevlishvili, Nucl.Phys. B807 (2009) 229,
”Inhomogeneous baryogenesis, cosmic antimatter, and dark matter”.
Massive PBHs allow to cure multpie inconsistencies with the standard
cosmology and astrophysics.
Unusual stellar type compact objects could also be created.
The model predicts the log-normal mass spectrum of PBH:dNdM= µ2 exp [−γ ln2 (M/M0 )],and predicts M0 ≈ 10M . A.Dolgov, K.Postnov, Why the mean mass ofprimordial black hole distribution is close to 10M . JCAP 07 (2020) 063 •e-Print: 2004.11669 . Very well agrees with observations.
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Anti-Creation Mechanism
SUSY motivated baryogenesis, Affleck and Dine (AD).
SUSY predicts existence of scalars with B 6= 0. Such bosons may condensealong flat directions of the quartic potential:
Uλ (χ) = λ|χ|4 (1 − cos 4θ)and of the mass term, Um = m 2 χ2 + m ∗ 2 χ∗ 2 :Um (χ) = m 2 |χ|2 [1 − cos (2θ + 2α)] ,where χ = |χ| exp (i θ) and m = |m|e α . If α 6= 0, C and CP are broken.
In GUT SUSY baryonic number is naturally non-conserved - non-invarianceof U(χ) w.r.t. phase rotation.

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Anti-Creation Mechanism
Initially (after inflation) χ is away from origin and, when inflation is over,starts to evolve down to equilibrium point, χ = 0, according to Newtonianmechanics:χ̈ + 3H χ̇ + U 0 (χ) = 0.
Baryonic charge of χ:Bχ = θ̇|χ|2
is analogous to mechanical angular momentum. χ decays transferredbaryonic charge to that of quarks in B-conserving process.
AD baryogenesis could lead to baryon asymmetry of order of unity, muchlarger than the observed 10−9 .
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Anti-Creation Mechanism
If m 6= 0, the angular momentum, B, is generated by a different directionof the quartic and quadratic valleys at low χ. If CP-odd phase α is small
but non-vanishing, both baryonic and antibaryonic domains might beformed with possible dominance of one of them.
Matter and antimatter domains may exist but globally B 6= 0.
Affleck-Dine field χ with CW potential coupled to inflaton Φ (AD andSilk; AD, Kawasaki, Kevlishvili):224

U = g |χ| (Φ − Φ1 ) + λ|χ| ln (|χ|2σ2)+λ1 (χ4 + h.c.) + (m 2 χ2 + h.c.).
Coupling to inflaton is the general renormalizable one.
When the window to the flat direction is open, near Φ = Φ1 , the field χslowly diffuses to large value, according to quantum diffusion equation
derived by Starobinsky, generalized to a complex field χ.
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Anti-Creation Mechanism
If the window to flat direction, when Φ ≈ Φ1 is open only during a shortperiod, cosmologically small but possibly astronomically large bubbles withhigh β could be created, occupying a small fraction of the universe, while
the rest of the universe has normal β ≈ 6 · 10−10 , created by small χ.
The mechanism of massive PBH formation quite different from all others.
The fundament of PBH creation is build at inflation by making large
isocurvature fluctuations at relatively small scales, with practicallyvanishing density perturbations.
Initial isocurvature perturbations are in chemical content of masslessquarks. Density perturbations are generated rather late after the QCD
phase transition.
The emerging universe looks like a piece of Swiss cheese, where holes arehigh baryonic density objects occupying a minor fraction of the universe
volume.
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Evolution of AD-field potential

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Evolution of AD-field

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Results of (Anti-)Creation
The outcome, depending on β = nB /nγ .
PBHs with log-normal mass spectrum - confirmed by the data!
Compact stellar-like objects, as e.g. cores of red giants.
Disperse hydrogen and helium clouds with (much) higher thanaverage nB density. Strange stars with unusual chemistry andvelocity.
β may be negative leading to creation of (compact?)
antistars which could survive annihilation with thehomogeneous baryonic background. Density is model
dependent but can be estimated using existing data on
PBHs.

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If true, the observation of antistars in the Galaxy is thediscovery of the Century.

More data are badly needed

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