17 research outputs found
Primordial Stochastic Gravitational Wave Background Anisotropies: in-in Formalization and Applications
Primordial non-Gaussianities of the scalar(tensor)-tensor-tensor type
supporting a non-trivial squeezed component are known to induce anisotropies in
the stochastic gravitational wave background. We derive the explicit form of
such anisotropies by making use, for the first time in this context, of the
in-in formalism for cosmological correlation functions. After illustrating the
general method and using it for the minimal single-field slow-roll case, we
apply it to multi-field models, providing both a tree-level and a one-loop
example. First, we make contact with previous results on anisotropies due to
the presence of an extra spin-2 field during inflation. Secondly, we calculate
the 1-loop scalar-tensor-tensor three-point function in the context of
so-called supersolid inflation. The corresponding gravitational wave anisotropy
is induced atop a gravitational signal that may be sufficiently large for
detection.Comment: 33 pages, 5 figure
Testing the early universe with anisotropies of the gravitational wave background
In this work we analyse in detail the possibility of using small and
intermediate-scale gravitational wave anisotropies to constrain the
inflationary particle content. First, we develop a phenomenological approach
focusing on anisotropies generated by primordial tensor-tensor-scalar and
purely gravitational non-Gaussianities. We highlight the quantities that play a
key role in determining the detectability of the signal. To amplify the power
of anisotropies as a probe of early universe physics, we consider
cross-correlations with CMB temperature anisotropies. We assess the size of the
signal from inflationary interactions against so-called induced anisotropies.
In order to arrive at realistic estimates, we obtain the projected constraints
on the non-linear primordial parameter for several upcoming
gravitational wave probes in the presence of the astrophysical gravitational
wave background. We further illustrate our findings by considering a concrete
inflationary realisation and use it to underscore a few subtleties in the
phenomenological analysis.Comment: 47 pages, 16 figure
Primordial gravitational waves in non-minimally coupled chromo-natural inflation
We consider inflation driven by an axion-like particle coupled to an SU(2) gauge sector via a Chern-Simons term. Known as chromo-natural inflation, this scenario is in tension with CMB observations. In order to remedy this fact and preserve both the symmetries and the intriguing gravitational wave phenomenology exhibited by the model, we explore the non-minimal coupling of the axion-inflaton to the Einstein tensor. We identify regions of parameter space corresponding to a viable cosmology at CMB scales. We also highlight the possibility of a non-trivial chiral gravitational wave signal at small scales.</p
Primordial stochastic gravitational wave background anisotropies: In-in formalization and applications
Primordial non-Gaussianities of the scalar(tensor)-tensor-tensor type supporting a non-trivial squeezed component are known to induce anisotropies in the stochastic gravitational wave background. We derive the explicit form of such anisotropies by making use, for the first time in this context, of the in-in formalism for cosmological correlation functions. After illustrating the general method and using it for the minimal single-field slow-roll case, we apply it to multi-field models, providing both a tree-level and a one-loop example. First, we make contact with previous results on anisotropies due to the presence of an extra spin-2 field during inflation. Secondly, we calculate the 1-loop scalar-tensor-tensor three-point function in the context of so-called supersolid inflation. The corresponding gravitational wave anisotropy is induced atop a gravitational signal that may be sufficiently large for detection
Enhancing gravitational wave anisotropies with peaked scalar sources
Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify in the process the relation between two different approaches to calculating GW anisotropies. We focus on GW scenarios sourced by a significantly peaked scalar spectrum, which are frequently considered in the context of primordial black holes production. We show that the resulting GW anisotropies are characterised by a distinct frequency dependence. We explore the observational consequences concentrating on a GW background enhanced in the frequency band of space-based GW detectors. We study the detectability of the signal through both cross-correlations among different space-based GW detectors, and among GW and CMB experiments
Enhancing gravitational wave anisotropies with peaked scalar sources
Gravitational wave (GW) backgrounds of cosmological origin are expected to be
nearly isotropic, with small anisotropies resembling those of the cosmic
microwave background. We analyse the case of a scalar-induced GW background and
clarify in the process the relation between two different approaches to
calculating GW anisotropies. We focus on GW scenarios sourced by a
significantly peaked scalar spectrum, which are frequently considered in the
context of primordial black holes production. We show that the resulting GW
anisotropies are characterised by a distinct frequency dependence. We explore
the observational consequences concentrating on a GW background enhanced in the
frequency band of space-based GW detectors. We study the detectability of the
signal through both cross-correlations among different space-based GW
detectors, and among GW and CMB experiments.Comment: 28 pages, 6 figure
New universal property of cosmological gravitational wave anisotropies
The anisotropies of the stochastic gravitational wave background, as produced
in the early phases of cosmological evolution, can act as a key probe of the
primordial universe particle content. We point out a new universal property of
gravitational wave anisotropies of cosmological origin: for adiabatic initial
conditions, their angular power spectrum is insensitive to the equation of
state of the cosmic fluid driving the expansion before big-bang
nucleosynthesis. Any deviation from this universal behaviour points to the
presence of non-adiabatic sources of primordial fluctuations. Such scenarios
can be tested by gravitational wave detectors operating at a frequency range
which is fully complementary to CMB experiments. In this work we prove this
general result, and we illustrate its consequences for a representative
realisation of initial conditions based on the curvaton scenario. In the case
of the simplest curvaton setup, we also find a significant cross-correlation
between gravitational wave anisotropies and the CMB temperature fluctuations.
There is a fourfold enhancement vis-\`{a}-vis the purely adiabatic scenario. We
discuss the implications of our findings for identifying the origin of the
(cosmological) gravitational wave background when, as is often the case, this
cannot be determined solely on the basis of its spectral shape.Comment: 14 pages, 4 figures. Version accepted at PR