Constraining graviton non-Gaussianity through the CMB bispectra

Luca, Valerio De; Franciolini, Gabriele; Kehagias, Alex; Riotto, Antonio; Shiraishi, Maresuke

doi:10.1103/physrevd.100.063535

Cited by 8 publications

(6 citation statements)

References 81 publications

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“…For r = 0.064 the expected tensor non gaussianity is high being f NL (ξ 5) 157, but it decreases with r: f NL (ξ 5) 10 for r = 0.01 and f NL (ξ 5) 0.31 for r = 0.001. These values are allowed by the present bounds on primordial non gaussianity [41][42][43][44]. In figure 6 we finally plot n t as a function of ξ for the same Figure 6: The tensor tilt as a function of ξ for three different values of the tensor to scalar ratio r: r = 0.064 (green line), r = 0.01 (blue line) and r = 0.001 (red line).…”

Section: Particle Production During Inflationmentioning

confidence: 92%

Probing the inflationary background of gravitational waves from large to small scales

Giarè,

Melchiorri

2020

Preprint

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The detection of Primordial Gravitational Waves (PGWs) is one of the most important goals of modern cosmology since PGWs can both provide substantial evidence for primordial inflation and shed light on its physical nature. Small scale experiments on gravitational waves such as Ligo-Virgo and, in future, LISA and Einstein Telescope (ET), are sensitive to the stochastic background, ΩGW. So they can be used to constrain the inflationary parameters. In performing this kind of analysis, as recently done also by the Planck collaboration, the primordial spectrum of gravitational waves is usually parametrized with a power law that includes only the amplitude and the spectral tilt. In this paper, we investigate the robustness of such constraints showing that the higher-order terms in the power law approximation (i.e. the runnings of the tensor tilt), even small on the CMB scales, can lead to non-negligible corrections on small scales. We start investigating these corrections in the simplest scenario of slow-roll inflation that predicts an almost scale-invariant, slightly red tilted primordial spectrum of gravitational waves. Nevertheless also in this case, fixing the tensor to scalar ratio to r = 0.064, we estimate a correction on ΩGW of about 39% on the Ligo-Virgo scales. Then we focus on blue models of inflation analyzing the robustness of the constraints that can be obtained using small scale measurements of the stochastic background. We prove that it is effectively possible to constrain the inflationary parameters on the CMB scales with the small scale data, but also that the higher-order corrections are nonnegligible on small scales. We provide an example of this, constraining with the Ligo Virgo data a physical model of blue inflation that employs a pseudo scalar axion naturally coupled to gauge fields, both including and neglecting the spectral runnings. For the same model, we also study the future constraints from the next generation of gravitational waves experiments such as Lisa and ET. We prove that, once the higher-order corrections are considered in the analysis, future experiments can tightly constraints the spectral tilt nt improving at least of an order of magnitude the constraints.

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Section: Particle Production During Inflationmentioning

confidence: 92%

Probing the inflationary background of gravitational waves from large to small scales

Giarè,

Melchiorri

2020

Preprint

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“…Due to the gauge dependence of Ω GW , it is natural to ask which gauge is relevant in interpreting the observations. This problem is solved by De Luca et al [75] where the authors argued that, for LISA-like GW detectors, the physical quantities are measured in synchronous gauge. The authors consider the time delay of a photon travelling between the two satellites of LISA.…”

Section: Gauge Issue Of Scalar Induced Gravitational Wavesmentioning

confidence: 99%

“…In [75,76,174], the authors calculated the SIGWs in the absence of E mode but considering its derivatives where the gauge freedom are completely fixed. In this situation, the energy density of SIGWs agrees with that in Newton gauge.…”

Section: Gauge Issue Of Scalar Induced Gravitational Wavesmentioning

confidence: 99%

Probing primordial–black-hole dark matter with scalar induced gravitational waves

2019

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The possibility that primordial black holes (PBHs) represent all of the dark matter (DM) in the Universe and explain the coalescences of binary black holes detected by LIGO/Virgo has attracted a lot of attention. PBHs are generated by the enhancement of scalar perturbations which inevitably produce the induced gravitational waves (GWs). We calculate the induced GWs up to the thirdorder correction which not only enhances the amplitude of induced GWs, but also extends the cutoff frequency from 2k * to 3k * . Such effects of the third-order correction lead to an around 10% increase of the signal-to-noise ratio (SNR) for both LISA and pulsar timing array (PTA) observations, and significantly widen the mass range of PBHs in the stellar mass window accompanying detectable induced GWs for PTA observations including IPTA, FAST and SKA. On the other hand, the null detections of the induced GWs by LISA and PTA experiments will exclude the possibility that all of the DM is comprised of PBHs and the GW events detected by LIGO/Virgo are generated by PBHs.

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“…It is worth stressing that these combinations are not realized by the usual parity-conserving theories like Einstein gravity (for which the sum defined in (4.57) has to be even) and therefore they can become robust indicators of parity breaking models with odd tensor bispectra if they are detected. According to the latest forecasts and previsions (see, e.g., [90,91,111,114]), forthcoming CMB experiments focusing on the polarization field (like, e.g., the LiteBIRD mission) will be able to probe order 1 amplitudes of tensor squeezed non-Gaussianities through the measurement of the CMB angular bispectra involving the B modes. This would justify a more detailed analysis of the detection prospects of these models in CMB angular bispectra in view of next experiments focusing on the search for the B-mode polarization field of the CMB.…”

Section: Comments and Observational Prospectsmentioning

confidence: 99%

Tensor non-Gaussianity in chiral scalar-tensor theories of gravity

Bartolo,

Caloni,

Orlando

et al. 2020

Preprint

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Violation of parity symmetry in the gravitational sector, which manifests into unequal left and right circular polarization states of primordial gravitational waves, represents a way to test high-energy modifications to general relativity. In this paper we study inflation within recently proposed chiral scalar-tensor theories of gravity, that extend Chern-Simons gravity by including parity-violating operators containing first and second derivatives of the non-minimally coupled scalar (inflaton) field. Given the degeneracy between different parityviolating theories at the level of the power spectrum statistics, we make a detailed analysis of the parity violation on primordial tensor non-Gaussianity. We show, with an explicit computation, that no new contributions arise in the graviton bispectra if the couplings in the new operators are constant in a pure de Sitter phase. On the other hand, if the coupling functions are time-dependent during inflation, the tensor bispectra acquire non-vanishing contributions from the parity-breaking operators even in the exact de Sitter limit, with maximal signal in the squeezed and equilateral configurations. We also comment on the consistency relation of the three-point function of tensor modes in this class of models and discuss prospects of detecting parity-breaking signatures through Cosmic Microwave Background B-mode bispectra.

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Constraining graviton non-Gaussianity through the CMB bispectra

Cited by 8 publications

References 81 publications

Probing the inflationary background of gravitational waves from large to small scales

Probing the inflationary background of gravitational waves from large to small scales

Probing primordial–black-hole dark matter with scalar induced gravitational waves

Tensor non-Gaussianity in chiral scalar-tensor theories of gravity

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