String cosmology: From the early universe to today

It is well-known that Dark Matter (DM) inside a satellite galaxy orbiting a host halo experiences a tidal potential. If DM is ultra-light, given its wave-like nature, one expects it to tunnel out of the satellite — if this happens sufficiently quickly, then the satellite will not survive over cosmological timescales, severely constraining this dark matter model. In this paper, we study the effects of the inevitable quartic self-interaction of scalar Ultra-Light Dark Matter (ULDM) on the lifetimes of satellite galaxies by looking for quasi-stationary solutions with outgoing wave boundary conditions. For a satellite with some known core mass and orbital period, we find that, attractive (repulsive) self-interactions decrease (increase) the rate of tunnelling of DM out of it. In particular, for satellite galaxies with core mass ∼𝒪(107–108) M⊙ and orbital period ∼𝒪(1) Gyr, one can impose constraints on the strength of self-interactions as small as λ∼𝒪(10-92). For instance, for ULDM mass m = 10-22 eV, the existence of the Fornax dwarf galaxy necessitates attractive self-interactions with λ≲ -2.12 × 10-91.

Section: Jcap02(2024)044mentioning

confidence: 99%

ULDM self-interactions, tidal effects and tunnelling out of satellite galaxies

Dave,

Goswami

2024

“…refs. [28][29][30][31][32]. In a contracting phase, a fluid with w ≫ 1 would wipe out all other contributions to the energy density before a big crunch, which would then followed by the standard thermal history of the universe.…”

Section: Phenomenological Descriptions Of Ekpyrosismentioning

confidence: 99%

Collapsing universe before time

Shiu,

Tonioni,

Tran

2024

In this note, we prove analytic bounds on the equation of state of a cosmological fluid composed of an arbitrary number of canonical scalars evolving in a negative multi-exponential potential. Because of the negative energy, the universe is contracting and eventually undergoes a big crunch. A contracting universe is a fundamental feature of models of ekpyrosis and cyclic universes, which are a proposed alternative to cosmic inflation to solve the flatness and horizon problems. Our analytic bounds set quantitative constraints on general effective theories of ekpyrosis. When applied to specific top-down constructions, our bounds can be used to determine whether ekpyrosis could in principle be realized. We point out some possible sources of tension in realizing the ekpyrotic universe in controlled constructions of string theory.

“…They could be produced in the early Universe by several mechanisms [18,19], such as vacuum misalignment [4][5][6], thermal production [20][21][22][23], collapse of cosmic strings and domain walls [24][25][26][27][28], decay of heavier particles (e.g. moduli or inflaton coupling to axions) [29][30][31][32][33][34][35] and Hawking radiation from primordial black holes [36][37][38]. For instance, in the misalignment mechanism, the induction of nonzero QCD axion mass by non-perturbative QCD instanton effects at around the QCD phase transition T ∼ Λ QCD triggers oscillations of the axion field that could yield the required amount of the dark matter in the Universe for QCD axions in mass range m a ∼ µeV, which is our main focus here.…”

Section: Introductionmentioning

confidence: 99%

On the Galactic radio signal from stimulated decay of axion dark matter

Bhupal Dev,

Ferrer,

Okawa

2024

We study the full-sky distribution of the radio emission from the stimulated decay of axions which are assumed to compose the dark matter in the Galaxy. Besides the constant extragalactic and CMB components, the decays are stimulated by a Galactic radio emission with a spatial distribution that we empirically determine from observations. We compare the diffuse emission to the counterimages of the brightest supernovæ remnants, and take into account the effects of free-free absorption. We show that, if the dark matter halo is described by a cuspy NFW profile, the expected signal from the Galactic center is the strongest. Interestingly, the emission from the Galactic anti-center provides competitive constraints that do not depend on assumptions on the uncertain dark matter density in the inner region. Furthermore, the anti-center of the Galaxy is the brightest spot if the Galactic dark matter density follows a cored profile. The expected signal from stimulated decays of axions of mass ma ∼ 10-6 eV is within reach of the Square Kilometer Array for an axion-photon coupling gaγ ≳ (2-3) × 10-11 GeV-1.