We reexamine production of primordial black holes in a supercooled phase transition. While a mere overdensity associated with a surviving false-vacuum patch does not imply formation of a black hole, it is possible for such a patch to evolve and create a black hole, thanks to the gradient energy stored in the bubble wall.

United States

France

Marcos M. Flores

Japan

Alexander Kusenko

Taiwan

Misao Sasaki

Revisiting formation of primordial black holes in a supercooled first-order phase transition

Supersymmetry predicts multiple flat directions, some of which carry a net baryon or lepton number. Condensates in such directions form during inflation and later fragment into <math><mrow><mi>Q</mi></mrow></math> balls, which can become the building blocks of primordial black holes. Thus, supersymmetry can create conditions for an intermediate matter-dominated era with black holes dominating the energy density of the Universe. Unlike particle matter, black holes decay suddenly enough to result in an observable gravitational wave signal via the poltergeist mechanism. We investigate the gravitational wave signatures of supersymmetry realized at energy scales that might not be accessible to present-day colliders.

CERN

Lauren Pearce

United Kingdom

Yuber F. Perez-Gonzalez

Graham White

Testing high scale supersymmetry via second order gravitational waves

We show that the present-day dark matter abundance can be produced through a novel mechanism that involves a very rapid thermal freeze-out caused by inhomogeneous heating and successive fast cooling of small fireballs in the early Universe. The fireballs can be produced from energy deposited in small scale structure growth induced by Yukawa interactions in certain particle species. Yukawa interactions are known to cause growth of halos even during a radiation dominated era, and the same interactions facilitate cooling and collapse of the halos by the emission of scalars. Energy deposited in the Standard Model plasma at the locations of the halo collapse can heat the plasma, re-establishing thermal equilibrium. The subsequent expansion and cooling of plasma fireballs leads to freeze-out of dark matter on timescales much shorter than the Hubble time. This mechanism can produce the right abundance of dark matter for masses and annihilation cross sections previously thought to be ruled out.

Greece

Chris Kouvaris

Defrosting and Blast Freezing Dark Matter

We show that viable electroweak baryogenesis can be realized without a first-order phase transition if plasma is heated inhomogeneously by nongravitational structure formation in some particle species. Yukawa interactions can mediate relatively long-range attractive forces in the early Universe. This creates an instability and leads to growth of structure in some species even during the radiation dominated era. At temperatures below the electroweak scale, the collapsing and annihilating halos can heat up plasma in fireballs that expand and create the out-of-equilibrium high-temperature environment suitable for generating the baryon asymmetry. The plasma temperature at the time of baryogenesis can be as low as a few MeV, making it consistent with both standard and low-reheat cosmologies.

Fireball baryogenesis from early structure formation due to Yukawa forces

Black holes may form in present-day collapse of microscopic structures of dark matter. We show that, if microstructure black holes (MSBH) with mass <math><mi>m</mi><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>13</mn></mrow></msup><mtext> g</mtext></math> are produced, the spectrum of gamma rays from their evaporation agrees remarkably well with the GeV excess observed by Fermi Gamma-ray Space Telescope, while still avoiding all observational constraints. We also discuss the generic requirements for MSBHs to explain the GeV excess.

Zachary S.C. Picker

Explaining the GeV excess with exploding black holes

Dark matter in the form of axions is expected to form axion stars. Such axion stars could be discovered by microlensing events. In particular, some candidate events reported by Subaru HSC and OGLE can be explained simultaneously if the axion stars with masses of the order of the Earth mass make up about <math><mo>∼</mo><msubsup><mrow><mn>27</mn></mrow><mrow><mo>−</mo><mn>13</mn></mrow><mrow><mo>+</mo><mn>7</mn></mrow></msubsup></math> percent of dark matter. For QCD axions, this corresponds to the axion mass in the range <math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>9</mn></mrow></msup><mo>−</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>6</mn></mrow></msup></math> eV, which is consistent with the experimental constraints, as well as the cosmological anthropic window of parameters.

Sunao Sugiyama

Masahiro Takada

Possible evidence of axion stars in HSC and OGLE microlensing events

Defect characterizes the depth of factorization of terms in differential (cyclotomic) expansions of knot polynomials, i.e. of the non-perturbative Wilson averages in the Chern-Simons theory. We prove the conjecture that the defect can be alternatively described as the degree in  $$q^{\pm 2}$$  <math> <msup> <mi>q</mi> <mrow> <mo>±</mo> <mn>2</mn> </mrow> </msup> </math>   of the fundamental Alexander polynomial, which formally corresponds to the case of no colors. We also pose a question if these Alexander polynomials can be arbitrary integer polynomials of a given degree. A first attempt to answer the latter question is a preliminary analysis of antiparallel descendants of the 2-strand torus knots, which provide a nice set of examples for all values of the defect. The answer turns out to be positive in the case of defect zero knots, what can be observed already in the case of twist knots. This proved conjecture also allows us to provide a complete set of C-polynomials for the symmetrically colored Alexander polynomials for defect zero. In this case, we achieve a complete separation of representation and knot variables.

Russia

E. Lanina

A. Morozov

Defect and degree of the Alexander polynomial

The nature of dark matter is one of the most important unsolved questions in science. Some dark matter candidates do not have sufficient nongravitational interactions to be probed in laboratory or accelerator experiments. It is thus important to develop astrophysical probes which can constrain or lead to a discovery of such candidates. We illustrate this using state-of-the-art measurements of strong gravitationally lensed quasars to constrain four of the most popular sterile neutrino models, and also report the constraints for other independent methods that are comparable in procedure. First, we derive effective relations to describe the correspondence between the mass of a thermal relic warm dark matter particle and the mass of sterile neutrinos produced via Higgs decay and grand unified theory (GUT)-scale scenarios, in terms of large-scale structure and galaxy formation astrophysical effects. Second, we show that sterile neutrinos produced through the Higgs decay mechanism are allowed only for mass <math><mo>&gt;</mo><mn>26</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></math>, and GUT-scale scenario <math><mo>&gt;</mo><mn>5.3</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></math>. Third, we show that the single sterile neutrino model produced through active neutrino oscillations is allowed for mass <math><mo>&gt;</mo><mn>92</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></math>, and the three sterile neutrino minimal standard model (<math><mrow><mi>ν</mi><mi>MSM</mi></mrow></math>) for mass <math><mo>&gt;</mo><mn>16</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></math>. These are the most stringent experimental limits on these models.

Ioana A. Zelko

Tommaso Treu

Kevork N. Abazajian

Canada

Daniel Gilman

Andrew J. Benson

Simon Birrer

Anna M. Nierenberg

Constraints on Sterile Neutrino Models from Strong Gravitational Lensing, Milky Way Satellites, and the Lyman-<math><mi>α</mi></math> Forest

Scalar fields which carry charge can generally form non-topological solitons (Q-balls), if the energy in the extended configuration is less than the energy of an equivalent number of free quanta. For global Q-balls, such solitons exist whenever the potential grows slower than quadratically. We show that even in the absence of attractive interactions, finite temperature corrections can generate Q-ball solutions, as the coefficient of cubic corrections is generally negative. As an illustration of this, we consider the possibility of constructing Q-balls using the Higgs field. We first show that the finite temperature corrections would enable the existence of Higgs balls if the Standard Model symmetry was ungauged. We then consider gauged Q-balls, following [1], and demonstrate that Higgs self-interactions mediated by the Standard Model gauge bosons are sufficient to prevent the existence of these states in the actual Standard Model. However, these states can exist in a variety of extensions, as we show explicitly through an example.

Generating non-topological solitons via thermal corrections: Higgs balls

In Affleck-Dine baryogenesis, the observed baryon asymmetry of the Universe is generated through the evolution of the vacuum expectation value of a scalar condensate. This scalar condensate generically fragments into nontopological solitons (<math><mrow><mi>Q</mi></mrow></math> balls). If they are sufficiently long-lived, they lead to an early matter domination epoch, which enhances the primordial gravitational wave signal for modes that enter the horizon during this epoch. The sudden decay of the <math><mrow><mi>Q</mi></mrow></math> balls results in a rapid transition from matter to radiation domination, producing a sharp peak in the gravitational wave power spectrum. Avoiding the gravitino over-abundance problem favors scenarios where the peak frequency of the resonance is within the range of the Einstein telescope and/or DECIGO. This observable signal provides a mechanism to test Affleck-Dine baryogenesis.