Simone Mercuri
Vacuum to vacuum instantonic transitions modify the power spectrum of primordial gravitational waves. We evaluate the new form of the power spectrum for ordinary gravity as well as the parity violation induced in the spectrum by a modification of General Relativity known as Holst term and we outline the possible experimental consequences.
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We study the halo mass function in the presence of the kurtosis type of primordial non-Gaussianity. The kurtosis corresponds to the trispectrum as defined in Fourier space. The primordial trispectrum is commonly characterized by two parameters, $τ_{\rm NL}$ and $g_{\rm NL}$. As applications of the derived non-Gaussian mass function, we consider the effect on the abundance of void structure, the effect on early star formation and on formation of the most massive object at high redshift. We show that by comparing the effects of primordial non-Gaussianity on cluster abundance with that on void ab…
Bulk of various astronomical observations of black holes suggest that virtually all observed black holes can be of primordial origin. A modified mechanism of the primordial black hole formation is described. A universal log-normal mass spectrum with a mean mass of around $\sim 10 M_\odot$ predicted by this mechanism is strongly confirmed by the LIGO/Virgo observations of gravitational waves from coalescing binary black holes.
Modifications to the primordial power spectrum of inflationary density perturbations have been studied recently using a boundary effective field theory approach. In the approximation of a fluctuating quantum field on a fixed background, the generic effect of new physics is encoded in parameters of order H/M. Here, we point out that the back-reaction on the metric can be neglected only when these parameters obey certain bounds that may put them beyond the reach of observation.
As a simple model for unknown Planck scale physics, we assume that the quantum modes responsible for producing primordial curvature perturbations during inflation are placed in their instantaneous adiabatic vacuum when their proper momentum reaches a fixed high energy scale M. The resulting power spectrum is derived and presented in a form that exhibits the amplitude and frequency of the superimposed oscillations in terms of H/M and the slow roll parameter epsilon. The amplitude of the oscillations is proportional to the third power of H/M. We argue that these small oscillations give the lower…
The huge amounts of undetected and exotic dark matter and dark energy needed to make general relativity work on large scales argue that we should investigate modifications of gravity. The only stable, metric-based and invariant alternative to general relativity is $f(R)$ models. These models can explain primordial inflation, but they cannot dispense with either dark matter or dark energy. I advocate nonlocal modifications of gravity, not as new fundamental theories but rather as the gravitational vacuum polarization engendered by infrared quanta produced during primordial inflation. I also dis…
The production of a stochastic background of relic gravitational waves is well known in various works in the literature, where, using the so called adiabatically-amplified zero-point fluctuations process it has been shown how the standard inflationary scenario for the early universe can in principle provide a distinctive spectrum of relic gravitational waves. In this paper, it is shown that a weak modification of General Relativity produces a third massive polarization of gravitational waves and the primordial production of this polarization is analysed adapting the adiabatically-amplified zer…
We derive a general expression for the power spectra of scalar and tensor fluctuations generated during inflation given an arbitrary choice of boundary condition for the mode function at a short distance. We assume that the boundary condition is specified at a short-distance cutoff at a scale $M$ which is independent of time. Using a particular prescription for the boundary condition at momentum $p = M$, we find that the modulation to the power spectra of density and gravitational wave fluctuations is of order $(H/M)$, where $H$ is the Hubble parameter during inflation, and we argue that this …
The enhancement of the spectrum of primordial comoving curvature perturbation $\R$ can induce the production of primordial black holes (PBH) which could account for part of present day dark matter. As an example of the effects of the modification of gravity on the production of PBHs, we investigate the effects on the spectrum of $\R$ produced by the modification of gravity in the case of G-inflation, deriving the relation between the unitary gauge curvature perturbation $ζ$ and the comoving curvature perturbation $\R$, and identifying a background dependent enhancement function $\E$ which can …
General relativistic effects on photon spectrum emitted from dark matter halos around primordial black holes
本文研究了原初黑洞周围暗物质晕发射光子谱的广义相对论效应，发现引力红移导致的谱线展宽可作为独特观测特征，为混合暗物质场景提供关键证据。
A possible origin of the anomalous dip and bump in the primordial power spectrum, which are reconstructed from WMAP data corresponding to the multipole $\ell=100\sim 140$ by using the inversion method, is investigated as a consequence of modification of scalar field dynamics in the inflation era. Utilizing an analytic formula to handle higher order corrections to the slow-roll approximation, we evaluate the relation between a detailed shape of inflaton potential and a fine structure in the primordial power spectrum. We conclude that it is unlikely to generate the observed dip and bump in the p…
We propose a mechanism to evade the Lyth bound in models of inflation. We minimally extend the conventional single-field inflation model in general relativity (GR) to a theory with non-vanishing graviton mass in the very early universe. The modification primarily affects the tensor perturbation, while the scalar and vector perturbations are the same as the ones in GR with a single scalar field at least at the level of linear perturbation theory. During the reheating stage, the graviton mass oscillates coherently and leads to resonant amplification of the primordial tensor perturbation. After r…
We study the generation of a large power spectrum, necessary for primordial black hole formation, within the effective theory of single-field inflation. The mechanisms we consider include a transition into a ghost-inflation-like phase and scenarios where an exponentially growing mode is temporarily turned on. In the cases we discuss, the enhancement in the power spectrum results from either a swift change in some effective coupling or a modification of the dispersion relation for the perturbations, while the background evolution remains unchanged and approximately de Sitter throughout inflatio…
Black holes in thermal bath live shorter: implications for primordial black holes
本研究证明热浴中的黑洞辐射谱受热化修正，衰变率改变，使暴胀后形成的极轻原初黑洞寿命缩短，具有重要宇宙学意义。
Primordial Black Hole Formation in Rastall Gravity: Shifted Collapse Threshold and Exponential Abundance Sensitivity
研究Rastall引力中原始黑洞的形成，发现该参数改变了坍缩动力学，影响密度波动增长、黑洞形成临界阈值和视界交叉时的波动幅度，表明原始黑洞形成对Rastall引力扰动层面的修改具有敏感性和独立探测能力。
We investigate the propagation of primordial gravitational waves within the context of the Horndeski theories, for this, we present a generalized transfer function quantifying the sub-horizon evolution of gravitational waves modes after they enter the horizon. We compare the theoretical prediction of the modified primordial gravitational waves spectral density with the aLIGO, Einstein telescope, LISA, gLISA and DECIGO sensitivity curves. Assuming reasonable and different values for the free parameters of the theory (in agreement with the event GW170817 and stability conditions of the theory), …
We study the effects of cold dark matter on the propagation of gravitational waves of astrophysical and primordial origin. We show that the dominant effect of cold dark matter on gravitational waves from astrophysical sources is a small frequency dependent modification of the propagation speed of gravitational waves. However, the magnitude of the effect is too small to be detected in the near future. We furthermore show that the spectrum of primordial gravitational waves in principle contains detailed information about the properties of dark matter. However, depending on the wavelength, the ef…
Probing modified Hawking evaporation with gravitational waves from the primordial black hole dominated universe
本文研究黑洞“记忆负担”效应对原初黑洞再加热情景的影响，发现该效应会延长PBH主导阶段、缩小允许质量范围，并可能通过诱导引力波谱的斜率检验霍金蒸发修正。
Inflation and Primordial Perturbations in Fractal Cosmology
研究分形宇宙学框架下的膨胀动力学，通过热力学修改在宇宙视界引入分形效应，推导修改后的慢-roll参数及其演化，分析不同势能对分形维度的影响，并与普朗克2018数据对比，约束有效维度范围。
We study the implications of deformed quantum algebras for the generation of primordial perturbations from slow-roll inflation. Specifically, we assume that the quantum commutator of the inflaton's amplitude and momentum in Fourier space gets modified at energies above some threshold $M_{\star}$. We show that when the commutator is modified to be a function of the momentum only, the problem of solving for the post-inflationary spectrum of fluctuations is formally equivalent to solving a one-dimensional Schrödinger equation with a time dependent potential. Depending on the class of modification…
We clarify the features of primordial non-Gaussianities of tensor perturbations in Gao's unifying framework of scalar-tensor theories. The general Lagrangian is given in terms of the ADM variables so that the framework maintains spatial covariance and includes the Horndeski theory and Gleyzes-Langlois-Piazza-Vernizzi (GLPV) generalization as specific cases. It is shown that the GLPV generalization does not give rise to any new terms in the cubic action compared to the case of the Horndeski theory, but four new terms appear in more general theories beyond GLPV. We compute the tensor 3-point cor…
Evaporation of Primordial Black Holes in a Thermal Universe: A Thermofield Dynamics Approach
研究热环境对黑洞霍金辐射的影响，采用热场动力学方法分析原初黑洞蒸发速率的变化及其宇宙学影响。
Cosmic topology. Part IIc. Detectability with non-standard primordial power spectrum
研究探讨了非标准原始功率谱对宇宙拓扑可检测性的影响，通过Kullback-Leibler散度和机器学习算法评估拓扑检测的观测前景。
We study aspects of inflation and the possibility of enhanced production of primordial black holes (PBHs) and gravitational waves (GWs) in a string-inspired model of two axion fields coupled to Chern-Simons gravity, which results in a running-vacuum-model inflation. Fluctuations of the scale invariant spectrum, consistent with the cosmological data, are provided in this model by world-sheet (non-perturbative) instanton terms of the axion field arising from string compactification. As a result of such modulations, there is an enhanced production of PBHs and GWs in such cosmologies, which may le…
In the context of modified teleparallel gravity, we study the generation of primordial density fluctuations in a general scalar-torsion theory whose Lagrangian density is an arbitrary function $f(T,ϕ)$ of the torsion scalar $T$ and a scalar field $ϕ$, plus the kinetic term of this latter. It is well known that generic modifications of teleparallel gravity are not invariant under six-parameter local Lorentz transformations. In order to restore the local Lorentz symmetry, we have incorporated six additional degrees of freedom in the form of Goldstone modes of the symmetry breaking through a Lore…
No constraints for $f(T)$ gravity from gravitational waves induced from primordial black hole fluctuations
本文研究原初黑洞涨落诱导的引力波对$f(T)$引力的约束，发现观测允许参数下偏差可忽略，表明可行$f(T)$理论可通过PBH约束。
We present a model that attempts to fuse the inflationary era and the subsequent radiation dominated era under a unified framework so as to provide a smooth transition between the two. The model is based on a modification of the generalized Chaplygin gas. We constrain the model observationally by mapping the primordial power spectrum of the scalar perturbations to the latest data of WMAP7. We compute as well the spectrum of the primordial gravitational waves as would be measured today.
Reconstructing inflationary features on large scales using genetic algorithm
本文通过遗传算法重构暴胀模型中的特征，改进CMB观测数据拟合，发现通过修改慢-roll参数函数形式可生成更优的功率谱特征，缓解现有宇宙学矛盾。
Measuring dark matter spikes around primordial black holes with Einstein Telescope and Cosmic Explorer
本文研究未来引力波探测器对原初黑洞周围暗物质尖峰的测量能力，提出可行形成情景并预测并合率，证明一周数据即可高精度测量双星与尖峰性质，同时警示忽略暗物质超密度效应会导致参数偏差或漏检。
Primordial Gravitational Wave Birefringence in a de Sitter Background with Chern-Simons Coupling
该研究探讨了德西特背景中陈-西蒙斯耦合对引力波双折射的影响，揭示了手性修正和宇称破坏性特征，并将陈-西蒙斯场与轴子状暗物质现象学联系起来。
Parametrization of the primordial power spectrum in loop quantum cosmology
本文研究了预膨胀 bounce 阶段对宇宙扰动角功率谱的印记，提出了一个新的原初功率谱参数化方法，结合了预膨胀物理和标准宇宙学参数，通过 NO-AHD 提议优化了真空选择，展示了在高多极数下与普朗克数据的优异一致性。
Sound Speed Resonance in the Gravitational Wave Background as a probe for non-standard early universe cosmologies
研究通过引力波背景中的声速共振探测早期宇宙非标准理论，分析共振如何增强原始张量模式信号以达到可检测水平。
Primordial Black Holes and Induced Gravitational Waves from a Smooth Crossover beyond Standard Model
本工作研究超出标准模型的平滑过渡导致$w$和$c^2_{\rm s}$软化的情况，数值计算次级诱导引力波，发现其信号特征可被探测并区分纯辐射情形，且场景与PBHs构成暗物质相容，引力波能解决质量函数简并性。
We consider an inflationary scenario in the holographic braneworld with a cosmological fluid occupying the 3+1 dimensional brane located at the holographic boundary of an asymptotic ADS$_5$ bulk. The contribution of the boundary conformal field can be represented as a modification of Einstein's equations on the boundary. Using these effective Einstein equations we calculate the cosmological perturbations and derive the corresponding power spectra assuming a general $k$-essence type of inflaton. We find that the braneworld scenario affects the scalar power spectrum only in the speed of sound de…
Pattern-recognition techniques to search for gravitational waves from inspiraling, dark-dressed primordial black holes
本文提出了一种基于模式识别技术的改进方法，用于检测由暗 dresses 包裹的原始黑洞发出的引力波信号，以提高对暗物质相关信号的识别能力。
PowerFull: fast and accurate computation of the relativistic angular galaxy power spectrum including local primordial non-Gaussianity
针对大视场星系巡天中相对论与广角效应显著的问题，本研究基于总角动量形式体系提出新的广角预测参数化方案，开发出可高效计算相对论性角功率谱的PowerFull工具，证实忽略相关效应会导致原初非高斯性参数$f_\text{NL}$的推断偏差。
Different effects of the Lorentz and Gaussian bump functions on the formation of primordial black holes and secondary gravitational waves
本文研究了洛伦兹和高斯突起函数对原初黑洞和引力波形成的影响，发现洛伦兹突起能更有效地增强功率谱并产生更多原初黑洞，同时产生更高能量密度的引力波。
Effects of the inflaton potential on the primordial power spectrum in Loop Quantum Cosmology scenarios
本文在圈量子宇宙学混合方案中将暴胀子势作为微扰，解析求解动能主导、过渡及慢滚暴胀各阶段的标量涨落，并用二次势定量分析原初功率谱。
A Nonlocal Realization of MOND that Interpolates from Cosmology to Gravitationally Bound Systems
本文提出一个非局部引力修正模型，能够插值引力束缚系统与宇宙学现象之间的MOND效应。
Scalar fields with an energy density dominated by its kinetic part may have played a relevant role in the very early stages of the Universe. Compared to the standard inflationary paradigm, they may lead to modifications in observable quantities, e.g. the anisotropies found in the cosmic microwave background. Kinetically dominated regimes arise in classical fast-roll scenarios as well as in quantum bouncing cosmologies. For instance, kinetic dominance is typical in interesting preinflationary phases of Loop Quantum Cosmology. In this work, we analyze the leading-order effects that the presence …
Constraining Modified Mass-to-Horizon Cosmology Through Primordial Inflationary Observables
本研究在广义质量-视界关系修正宇宙学中分析慢滚暴胀，发现Starobinsky模型对参数n高度敏感，并通过对标量功率谱归一化施加0.960≤n≤1.040的严格约束，表明暴胀可作为广义视界热力学的灵敏探针。
The small-scale crisis, discrepancies between observations and N-body simulations, may imply suppressed matter fluctuations on subgalactic distance scales. Such a suppression could be caused by some early-universe mechanism (e.g., broken scale invariance during inflation), leading to a modification of the primordial power spectrum at the onset of the radiation-domination era. Alternatively, it may be due to nontrivial dark-matter properties (e.g., new dark-matter interactions or warm dark matter) that affect the matter power spectrum at late times, during radiation domination, after the pertur…
We investigate the new observational constraints on $f(T)$ gravity that arise from the effects of primordial gravitational waves (GWs) on the cosmic microwave background (CMB) anisotropies and the BB spectrum. We first show that on the GWs propagation in $f(T)$ gravity we obtain only an amplitude modification and not a phase one, comparing to the case of general relativity in the background of $Λ$CDM cosmology. Concerning primordial GWs we find that the more the model departs from general relativity the larger is the GW amplitude decay, and thus a possible future detection would bring the viab…
As previously discussed in (D. Sudarsky, Int.J.Mod.Phys.D20:509-552, (2011); [arXiv:0906.0315]), the inflationary account for the emergence of the seeds of cosmic structure falls short of actually explaining the generation of primordial anisotropies and inhomogeneities. This description starts from a symmetric background, and invokes symmetric dynamics, so it cannot explain asymmetries. To generate asymmetries, we present an application of the Continuous Spontaneous Localization (CSL) model of wave function collapse (P. Pearle, Phys. Rev. A 39, 2277, (1989); G. C. Ghirardi, P. Pearle and A. Ri…
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