Impact of kinetic and potential self-interactions on scalar dark matter

Brax, Philippe; Valageas, Patrick; Cembranos, J. A. R.

doi:10.1103/physrevd.100.023526

Cited by 26 publications

(61 citation statements)

References 79 publications

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“…We have also noted that the de Broglie wavelength of the φ field with m φ ∼ 10 −14 eV is much below the kpc scale characteristic for fuzzy DM with the mass of order 10 −22 eV. However, in the presence of sizeable repulsive φ self-interactions, even much heavier fields can lead to large solitonic structures in DM dense regions in galaxies [32,58]. While we have a priori not introduced such interactions in our scenario, they will be induced at the loop level by the exchange of heavy χ fields, cf.…”

Section: Creation and Size Of φ Dm Solitonsmentioning

confidence: 69%

Co-interacting dark matter and conformally coupled light scalars

Brax,

van de Bruck,

Trojanowski

2021

Preprint

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The increasing observational pressure on the standard cosmological model motivates analyses going beyond the paradigm of the collision-less cold dark matter (DM). Since the only clear evidence for the existence of DM is based on gravitational interactions, it seems particularly fitting to study them in this sector where extensions to the standard model can be naturally introduced. A promising avenue can be obtained using modifications of the space-time metric coupled to DM and induced by the presence of a new ultra-light scalar field φ. The φ field can contribute to the DM density and can couple all the matter species universally, including additional heavy DM particles. We present a simple two-component DM model employing derivative conformal interactions between the two DM species. This can simultaneously: 1) guarantee the necessary symmetries to stabilize the dark species, 2) predict a subdominant thermal relic density of the heavy DM component, and 3) alleviate small-scale structure tensions of the cold DM scenario due to the possible co-interactions in the dark sector. The scenario is highly predictive with future observational prospects ranging from the Large Hadron Collider (LHC) to gravitational-wave searches, and can be generalized to more rich and realistic dark sector models.

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Section: Creation and Size Of φ Dm Solitonsmentioning

confidence: 69%

Co-interacting dark matter and conformally coupled light scalars

Brax,

van de Bruck,

Trojanowski

2021

Preprint

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“…where the leading term proportional to λ is consistent with the results of refs. [9,40]. And, finally, the bulk viscosity coefficient reads We are not making any assumption about the relative fraction of the energy densities.…”

Section: Jhep07(2020)059mentioning

confidence: 99%

Effective theories for a nonrelativistic field in an expanding universe: Induced self-interaction, pressure, sound speed, and viscosity

Salehian

Namjoo

Kaiser

2020

J. High Energ. Phys.

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A massive, nonrelativistic scalar field in an expanding spacetime is usually approximated by a pressureless perfect fluid, which leads to the standard conclusion that such a field can play the role of cold dark matter. In this paper, we systematically study these approximations, incorporating subleading corrections. We provide two equivalent effective descriptions of the system, each of which offers its own advantages and insights: (i) A nonrelativistic effective field theory (EFT) with which we show that the relativistic corrections induce an effective self-interaction for the nonrelativistic field. As a byproduct, our EFT also allows one to construct the exact solution, including oscillatory behavior, which is often difficult to achieve from the exact equations. (ii) An effective (imperfect) fluid description, with which we demonstrate that, for a perturbed Friedmann-Lemaître-Robertson-Walker (FLRW) universe: (a) The pressure is small but nonzero (and positive), even for a free theory with no tree-level self-interactions. (b) The sound speed of small fluctuations is also nonzero (and positive), reproducing already known leading-order results, correcting a subdominant term, and identifying a new contribution that had been omitted in previous analyses. (c) The fluctuations experience a negative effective bulk viscosity. The positive sound speed and the negative bulk viscosity act in favor of and against the growth of overdensities, respectively. The net effect may be considered a smoking gun for ultra-light dark matter.

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“…Notice that this is different from [63], where the two terms have the same order of magnitude. In the nonrelativistic regime, where we average over the fast oscillations of the scalar field, the effective interaction potential becomes [33]…”

Section: A Cosine Potentialmentioning

confidence: 99%

“…In the simplest case, called fuzzy dark matter [12,13], a massive scalar field oscillating around its vacuum expectation value (vev), and with a sufficiently low mass m ≲ 10 −21 eV, could play the role of dark matter. The resulting properties of these scalar dark-matter models are similar to the standard cold dark matter (CDM) for the formation of large-scale structures [14][15][16][17][18][19][20][21], but not for small scales, where distinctive features such as a nonvanishing speed of sound can leave different observational signatures [19,20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

Section: Introductionmentioning

confidence: 99%

“…When self-interactions are present and overcome the quantum pressure, which can happen for masses larger than 10 −21 eV, it is known that a repulsive pressure can also result from positive interaction potentials like ϕ 4 . In this case, large solitons can also form by gravitational instability and eventually stabilize when the gravitational attraction becomes balanced by the scalar self-repulsion [33][34][35][36]. In all these cases, dark matter is essentially a smooth fluid with large overdensities in the core of solitonic objects, which have galactic sizes and could play the role of galactic dark matter halos with a smooth inner region.…”

Section: Introductionmentioning

confidence: 99%

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Nonrelativistic formation of scalar clumps as a candidate for dark matter

2020

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We propose a new mechanism for the formation of dark matter clumps in the radiation era. We assume that a light scalar field is decoupled from matter and oscillates harmonically around its vacuum expectation value. We include self-interactions and consider the nonrelativistic regime. The scalar dynamics are described by a fluid approach where the fluid pressure depends on both quantum and self-interaction effects. When the squared speed of sound of the scalar fluid becomes negative, an instability arises and the fluctuations of the scalar energy-density field start growing. They eventually become nonlinear and clumps form. Subsequently, the clumps aggregate and reach a universal regime. Afterwards, they play the role of cold dark matter. We apply this mechanism first to a model with a negative quartic term stabilized by a positive self-interaction of order six, and then to axion monodromy, where a subdominant cosine potential corrects a mass term. In the first case, the squared speed of sound becomes negative when the quartic term dominates, leading to a tachyonic instability. For axion monodromy, the instability starts very slowly after the squared speed of sound first becomes negative and then oscillates around zero. Initially the density perturbations perform acoustic oscillations due to the quantum pressure. Eventually, they start growing exponentially due to a parametric resonance. The shape and the scaling laws of the clumps depend on their formation mechanism. When the tachyonic phase takes place, the core density of the clumps is uniquely determined by the energy density at the beginning of the instability. On the other hand, for axion monodromy, the core density scales with the soliton mass and radius. This difference comes from the crucial role that the quantum pressure plays in both the parametric resonance in the linear regime and in the nonlinear formation regime of static scalar solitons. In both scenarios, the scalar-field clumps span a wide range of scales and masses, running from the size of atoms to that of galactic molecular clouds, and from 10 −3 gram to thousands of solar masses. Because of finite-size effects, both from the source and the lens, these dark matter clumps are far beyond the reach of microlensing observations. We find that the formation redshift of the scalar clumps can span a large range in the radiation era; the associated background temperature can vary from 10 eV to 10 5 GeV, and the scalar-field mass from 10 −26 GeV to 10 GeV.

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Impact of kinetic and potential self-interactions on scalar dark matter

Cited by 26 publications

References 79 publications

Co-interacting dark matter and conformally coupled light scalars

Co-interacting dark matter and conformally coupled light scalars

Effective theories for a nonrelativistic field in an expanding universe: Induced self-interaction, pressure, sound speed, and viscosity

Nonrelativistic formation of scalar clumps as a candidate for dark matter

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