35 research outputs found

### Comparing Accretion Disks and Dark Matter Spikes in Intermediate Mass Ratio Inspirals

Intermediate Mass Ratio Inspirals (IMRIs) will be observable with space-based
gravitational wave detectors such as the Laser Interferometer Space Antenna
(LISA). To this end, the environmental effects in such systems have to be
modeled and understood. These effects can include (baryonic) accretion disks
and dark matter (DM) overdensities, so called spikes. For the first time, we
model an IMRI system with both an accretion disk and a DM spike present and
compare their effects on the inspiral and the emitted gravitational wave
signal. We study the eccentricity evolution, employ the braking index and
derive the dephasing index, which turn out to be complementary observational
signatures. They allow us to disentangle the accretion disk and DM spike
effects in the IMRI system.Comment: 16 pages, 8 figures. Submitted to PRD. Code available online at
http://github.com/DMGW-Goethe/imrip

### Fermion Proca Stars: Vector Dark Matter Admixed Neutron Stars

Dark matter could accumulate around neutron stars in sufficient amounts to
affect their global properties. In this work, we study the effect of a specific
model for dark matter -- a massive and self-interacting vector (spin-1) field
-- on neutron stars. We describe the combined systems of neutron stars and
vector dark matter using Einstein-Proca theory coupled to a nuclear-matter
term, and find scaling relations between the field and metric components in the
equations of motion. We construct equilibrium solutions of the combined
systems, compute their masses and radii and also analyse their stability and
higher modes. The combined systems admit dark matter (DM) core and cloud
solutions. Core solutions compactify the neutron star component and tend to
decrease the total mass of the combined system. Cloud solutions have the
inverse effect. Electromagnetic observations of certain cloud-like
configurations would appear to violate the Buchdahl limit. This could make
Buchdahl-limit violating objects smoking gun signals for dark matter in neutron
stars. The self-interaction strength is found to significantly affect both mass
and radius. We also compare fermion Proca stars to objects where the dark
matter is modelled using a complex scalar field. We find that fermion Proca
stars tend to be more massive and geometrically larger than their scalar field
counterparts for equal boson masses and self-interaction strengths. Both
systems can produce degenerate masses and radii for different amounts of DM and
DM particle masses.Comment: 20 pages, 11 figures, superseeds arXiv:2308.1217

### On the Soft Limit of the Large Scale Structure Power Spectrum: UV Dependence

We derive a non-perturbative equation for the large scale structure power
spectrum of long-wavelength modes. Thereby, we use an operator product
expansion together with relations between the three-point function and power
spectrum in the soft limit. The resulting equation encodes the coupling to
ultraviolet (UV) modes in two time-dependent coefficients, which may be
obtained from response functions to (anisotropic) parameters, such as spatial
curvature, in a modified cosmology. We argue that both depend weakly on
fluctuations deep in the UV. As a byproduct, this implies that the renormalized
leading order coefficient(s) in the effective field theory (EFT) of large scale
structures receive most of their contribution from modes close to the
non-linear scale. Consequently, the UV dependence found in explicit
computations within standard perturbation theory stems mostly from
counter-term(s). We confront a simplified version of our non-perturbative
equation against existent numerical simulations, and find good agreement within
the expected uncertainties. Our approach can in principle be used to precisely
infer the relevance of the leading order EFT coefficient(s) using small volume
simulations in an `anisotropic separate universe' framework. Our results
suggest that the importance of these coefficient(s) is a $\sim 10 \%$ effect,
and plausibly smaller.Comment: 25+5 pages, 10 figures, comments added, matches published versio

### Neutrino mass bounds from confronting an effective model with BOSS Lyman-alpha data

We present an effective model for the one-dimensional Lyman-$\alpha$ flux
power spectrum far above the baryonic Jeans scale. The main new ingredient is
constituted by a set of two parameters that encode the impact of small, highly
non-linear scales on the one-dimensional power spectrum on large scales, where
it is measured by BOSS. We show that, by marginalizing over the model
parameters that capture the impact of the intergalactic medium, the flux power
spectrum from both simulations and observations can be described with high
precision. The model displays a degeneracy between the neutrino masses and the
(unknown, in our formalism) normalization of the flux power spectrum. This
degeneracy can be lifted by calibrating one of the model parameters with
simulation data, and using input from Planck CMB data. We demonstrate that this
approach can be used to extract bounds on the sum of neutrino masses with
comparably low numerical effort, while allowing for a conservative treatment of
uncertainties from the dynamics of the intergalactic medium. An explorative
analysis yields an upper bound of $0.16\,$eV at $95\%$ C.L. when applied to
BOSS data at $3\leq z\leq 4.2$. We also forecast that if the systematic and
statistical errors will be reduced by a factor two the upper bound will become
$0.1\,$eV at $95\%$ C.L.Comment: 27 pages, 11 figure

### On Soft Limits of Large-Scale Structure Correlation Functions

We study soft limits of correlation functions for the density and velocity
fields in the theory of structure formation. First, we re-derive the (resummed)
consistency conditions at unequal times using the eikonal approximation. These
are solely based on symmetry arguments and are therefore universal. Then, we
explore the existence of equal-time relations in the soft limit which, on the
other hand, depend on the interplay between soft and hard modes. We scrutinize
two approaches in the literature: The time-flow formalism, and a background
method where the soft mode is absorbed into a locally curved cosmology. The
latter has been recently used to set up (angular averaged) `equal-time
consistency relations'. We explicitly demonstrate that the time-flow relations
and `equal-time consistency conditions' are only fulfilled at the linear level,
and fail at next-to-leading order for an Einstein de-Sitter universe. While
applied to the velocities both proposals break down beyond leading order, we
find that the `equal-time consistency conditions' quantitatively approximates
the perturbative results for the density contrast. Thus, we generalize the
background method to properly incorporate the effect of curvature in the
density and velocity fluctuations on short scales, and discuss the reasons
behind this discrepancy. We conclude with a few comments on practical
implementations and future directions.Comment: 22 pages, extended discussion, v3: matches published versio

### Prospects for axion searches with Advanced LIGO through binary mergers

The observation of gravitational waves from a binary neutron star merger by
LIGO/VIRGO and the associated electromagnetic counterpart provides a high
precision test of orbital dynamics, and therefore a new and sensitive probe of
extra forces and new radiative degrees of freedom. Axions are one particularly
well-motivated class of extensions to the Standard Model leading to new forces
and sources of radiation, which we focus on in this paper. Using an effective
field theory (EFT) approach, we calculate the first post-Newtonian corrections
to the orbital dynamics, radiated power, and gravitational waveform for binary
neutron star mergers in the presence of an axion. This result is applicable to
many theories which add an extra massive scalar degree of freedom to General
Relativity. We then perform a detailed forecast of the potential for Advanced
LIGO to constrain the free parameters of the EFT, and map these to the mass
$m_a$ and decay constant $f_a$ of the axion. At design sensitivity, we find
that Advanced LIGO can potentially exclude axions with $m_a \lesssim 10^{-11} \
{\rm eV}$and$f_a \sim (10^{14} - 10^{17}) \ {\rm GeV}$. There are a variety
of complementary observational probes over this region of parameter space,
including the orbital decay of binary pulsars, black hole superradiance, and
laboratory searches. We comment on the synergies between these various
observables.Comment: 22 pages, 11 figures, 1 table, some equations corrected, typos fixed,
references and discussion added, to appear in PR

### Tidal Deformability of Fermion-Boson Stars: Neutron Stars Admixed with Ultra-Light Dark Matter

In this work we investigate the tidal deformability of a neutron star admixed
with dark matter, modeled as a massive, self-interacting, complex scalar field.
We derive the equations to compute the tidal deformability of the full
Einstein-Hilbert-Klein-Gordon system self-consistently, and probe the influence
of the scalar field mass and self-interaction strength on the total mass and
tidal properties of the combined system. We find that dark matter core-like
configurations lead to more compact objects with smaller tidal deformability,
and dark matter cloud-like configurations lead to larger tidal deformability.
Electromagnetic observations of certain cloud-like configurations would appear
to violate the Buchdahl limit. The self-interaction strength is found to have a
significant effect on both mass and tidal deformability. We discuss
observational constraints and the connection to anomalous detections. We also
investigate how this model compares to those with an effective bosonic equation
of state and find the interaction strength where they converge sufficiently.Comment: 14 pages, 7 figures; Accepted for publicatio

### The Time-Flow Approach as a Tool for Large-Scale Structure

We discuss how the time-flow approach of cosmological perturbation theory can be used as a tool for large-scale structure. In particular, we show that the flow equations allow to derive straightforwardly consistency relations for equal-time correlators involving both density and velocity fields and underlying different background cosmologies. Furthermore, we use the time-flow approach to proof the intricate cancellation of soft loop momenta in the power spectrum of standard perturbation theory at any loop order