Last year, two separate experimental groups, Oliver H. E. Philcox et al. and Hou et al., reported claims of parityviolating signatures in the connected fourpoint correlation function of the matter overdensity field δ(t, x), which is often referred to as the galaxyfour point correlation function. The matter overdensity field parametrizes the excess of matterenergy density with respect to the homogeneous background and it’s defined as δ(t, x) ≡ (δρ(t,x)−ρ¯(t))/ ρ¯(t) , where ρ(t, x) is the energy density field and ρ¯(t) is the average density field. The fourpoint correlation function is the most simple statistic capable of detecting parity violation in the case of a scalar field. The galaxy fourpoint correlation function basically quantifies the excess of quartets of galaxies compared to a random distribution. If these measurements are confirmed, they would have two fundamental implications. First of all, the detection of a connected correlator beyond the twopoint statistic serves as possible evidence of primordial nonGaussianity. Moreover, since we know that weak forces play no role in the formation of largescale structures it would be evidence of new physics. The goal of this work is to investigate the possibility to formulate an inflationary model capable of leaving parityviolating imprints on latetimes observables. Consequently, we examine the inflationary phase within the framework of parityviolating theories of modified gravity. We need to modify the standard scenario of singlefield slowroll Inflation with standard gravitational interaction since it is parityconserving. We examine the dynamical ChernSimons (dCS) theory of modified gravity, which extends the standard inflationary model with the lowestorder parity violating coupling between the inflaton and the graviton. In this context, we demonstrate that dCS leaves a distinctive parityviolating signature in the primordial trispectrum of scalar perturbations. However, the signal is too weak to account for the observed parity violation. Thus, we explore alternative theories where, a priori, an enhancement is feasible due to gravitational waves’ birefringence, i.e. the two chiral polarizations, left and right, of the graviton propagate at different speeds. We present an original analysis of the gravitonmediated trispectrum in the case of the chiralscalar tensor theories of gravity. The gravitonmediated trispectrum is the leading parityviolating contribution to the Fourier transform of the fourpoint correlation function. The theories we analyze extend ChernSimons gravity by including parityviolating operators containing first and second derivatives of the nonminimally coupled inflaton field. We manage to generate a parityviolating signal, but we don’t observe any significant enhancement compared to the previous scenario.
Parityviolation signatures in the largescale distribution of galaxies
MORETTI, TOMMASO
2022/2023
Abstract
Last year, two separate experimental groups, Oliver H. E. Philcox et al. and Hou et al., reported claims of parityviolating signatures in the connected fourpoint correlation function of the matter overdensity field δ(t, x), which is often referred to as the galaxyfour point correlation function. The matter overdensity field parametrizes the excess of matterenergy density with respect to the homogeneous background and it’s defined as δ(t, x) ≡ (δρ(t,x)−ρ¯(t))/ ρ¯(t) , where ρ(t, x) is the energy density field and ρ¯(t) is the average density field. The fourpoint correlation function is the most simple statistic capable of detecting parity violation in the case of a scalar field. The galaxy fourpoint correlation function basically quantifies the excess of quartets of galaxies compared to a random distribution. If these measurements are confirmed, they would have two fundamental implications. First of all, the detection of a connected correlator beyond the twopoint statistic serves as possible evidence of primordial nonGaussianity. Moreover, since we know that weak forces play no role in the formation of largescale structures it would be evidence of new physics. The goal of this work is to investigate the possibility to formulate an inflationary model capable of leaving parityviolating imprints on latetimes observables. Consequently, we examine the inflationary phase within the framework of parityviolating theories of modified gravity. We need to modify the standard scenario of singlefield slowroll Inflation with standard gravitational interaction since it is parityconserving. We examine the dynamical ChernSimons (dCS) theory of modified gravity, which extends the standard inflationary model with the lowestorder parity violating coupling between the inflaton and the graviton. In this context, we demonstrate that dCS leaves a distinctive parityviolating signature in the primordial trispectrum of scalar perturbations. However, the signal is too weak to account for the observed parity violation. Thus, we explore alternative theories where, a priori, an enhancement is feasible due to gravitational waves’ birefringence, i.e. the two chiral polarizations, left and right, of the graviton propagate at different speeds. We present an original analysis of the gravitonmediated trispectrum in the case of the chiralscalar tensor theories of gravity. The gravitonmediated trispectrum is the leading parityviolating contribution to the Fourier transform of the fourpoint correlation function. The theories we analyze extend ChernSimons gravity by including parityviolating operators containing first and second derivatives of the nonminimally coupled inflaton field. We manage to generate a parityviolating signal, but we don’t observe any significant enhancement compared to the previous scenario.File  Dimensione  Formato  

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https://hdl.handle.net/20.500.12608/55396