Search

We show that the static tidal Love number of Schwarzschild black holes in four dimensions and in the vacuum vanishes at any order in the external tidal force. We also identify the underlying non-linear symmetry which is responsible for this result and becomes manifest when the black hole metric is written in axsymmetric static Weyl coordinates., Comment: 13 pages, LaTeX file

We provide a simple proof of why the Love number vanishes for extremal Reissner-Nordstrom and Kerr-Newman black holes. The argument is based on a conformal inversion isometry of the spacetime connecting the horizon with large distances., Comment: 6 pages

We show why the threshold for primordial black hole formation is universal (independent from the shape of the perturbation) when expressed in terms of the volume averaged compaction function. The proof is rooted in the self-similarity of the gravitational collapse phenomenon at criticality., Comment: 7 pages

We revisit the genuine Fayet-Iliopoulos terms of 4D N=1 supergravity. Such terms are commonly believed to preserve a global symmetry, and therefore they are in conflict with the principles of quantum gravity. However, we find that generically there do exist supersymmetric terms that break explicitly the specific global symmetry, while preserving gauge invariance. We illustrate this, by providing a series of examples, including superpotentials and superspace higher order terms, along with a general prescription for their construction., Comment: 17 pages

We provide evidence for a correspondence between the formation of black holes and the stability of circular null geodesics around the collapsing perturbation. We first show that the critical threshold of the compaction function to form a black hole in radiation is well approximated by the critical threshold for the appearance of the first unstable circular orbit in a spherically symmetric background. We also show that the critical exponent in the scaling law of the primordial black hole mass close to the threshold is set by the inverse of the Lyapunov coefficient of the unstable orbits when a self-similar stage is developed close to criticality., Comment: 5 pages, 4 figures v2: Updated version matching the PRL published version

The Hellings and Downs correlation curve describes the correlation of the timing residuals from pairs of pulsars as a function of their angular separation on the sky and is a smoking-gun signature for the detection of an isotropic stochastic background of gravitational waves. We show that it can be easily obtained from realizing that Lorentz transformations are conformal transformations on the celestial sphere and from the conformal properties of the two-point correlation of the timing residuals. This result allows several generalizations, e.g. the calculation of the three-point correlator of the time residuals and the inclusion of additional polarization modes (vector and/or scalar) arising in alternative theories of gravity., Comment: 22 pages, 2 figures

An extended search for anomaly free matter coupled $N=(1,0)$ supergravity in six dimension is carried out by two different methods which we refer to as the graphical and rank methods. In the graphical method the anomaly free models are built from single gauge group models, called nodes, which can only have gravitational anomalies. We search for anomaly free theories with gauge groups $G_1\times...\times G_n$ with $n=1,2,...$ (any number of factors) and $G_1\times...\times G_n \times U(1)_R$ where $n=1,2,3$ and $U(1)_R$ is the $R$-symmetry group. While we primarily consider models with the tensor multiplet number $n_T=1$, we also provide some results for $n_T\ne 1$ with an unconstrained number of charged hypermultiplets. We find a large number of ungauged anomaly free theories. However, in the case of $R$-symmetry gauged models with $n_T=1$, in addition to the three known anomaly free theories with $G_1\times G_2 \times U(1)_R$ type symmetry, we find only six new remarkably anomaly free models with symmetry groups of the form $G_1\times G_2\times G_3 \times U(1)_R$. In the case of $n_T=1$ and ungauged models, excluding low rank group factors and considering only low lying representations, we find all anomaly free theories. Remarkably, the number of group factors does not exceed four in this class. The proof of completeness in this case relies on a bound which we establish for a parameter characterizing the difference between the number of non-singlet hypermultiplets and the dimension of the gauge group., Comment: 42 pp + 33 pp apendix, 3 figures, 2 tables

The formation of primordial black holes in the early universe may happen through the collapse of large curvature perturbations generated during a non-attractor phase of inflation or through a curvaton-like dynamics after inflation. The fact that such small-scale curvature perturbation is typically non-Gaussian leads to the renormalization of composite operators built up from the smoothed density contrast and entering in the calculation of the primordial black abundance. Such renormalization causes the phenomenon of operator mixing and the appearance of an infinite tower of local, non-local and higher-derivative operators as well as to a sizable shift in the threshold for primordial black hole formation. This hints that the calculation of the primordial black hole abundance is more involved than what generally assumed., Comment: 23 pages, 2 figures

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more km-scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions., Comment: Summary of the Terrestrial Very-Long-Baseline Atom Interferometry Workshop held at CERN: https://indico.cern.ch/event/1208783/

Due to the nature of gravity, non-linear effects are left imprinted in the quasi-normal modes generated in the ringdown phase of the merger of two black holes. We offer an analytical treatment of the quasi-normal modes at second-order in black hole perturbation theory which takes advantage from the fact that the non-linear sources are peaked around the light ring. As a byproduct, we describe why the amplitude of the second-order mode relative to the square of the first-order amplitude depends only weakly on the initial condition of the problem., Comment: 23 pages, 4 figures, V2, published version

We discuss the non-linear corrections entering in the calculation of the primordial black hole abundance from the non-linear radiation transfer function and the determination of the true physical horizon crossing. We show that the current standard techniques to calculate the abundance of primordial black holes suffer from uncertainties and argue that the primordial black hole abundance may be much smaller than what routinely considered. This would imply, among other consequences, that the interpretation of the recent pulsar timing arrays data from scalar-induced gravitational waves may not be ruled out because of an overproduction of primordial black holes., Comment: 12 pages, 3 figures. v2: matching published version

We note that the typical gauge mediation of supersymmetry breaking is in tension with the global limit of the festina lente swampland bound. The alternatives are mediation/breaking schemes that decouple together with gravity, as for example gravity mediation, for which we highlight some basic phenomenological properties. Gauge mediation remains instead a viable mechanism only in models where supersymmetry is restored in the global limit, as for example in no-scale supergravity., Comment: 7 pages, accepted in PLB

The Weak Gravity Conjecture predicts that in quantum gravity there should exist overcharged states, that is states with charge larger than their mass. Extending this to large masses and charges, we are expecting similar overcharged classical solutions. This has been demonstrated in higher-derivative extensions of General Relativity. In this paper we investigate the existence of overcharged solutions in General Relativity. We study the dynamics of a thin shell of mass $m$ and charge $Q$ under the action of its own gravitational and $U(1)$ fields. We show that shells with surface energy $\sigma$ and pressure $P$ obeying $P=w\sigma$ with $0\leq w\leq 1$ are necessarily undercharged $m\geq |Q|$ and always collapse to form Reissner-Nordstr\"om black holes. Nevertheless, if $-1\leq w<0$, we find that overcharged $m\leq |Q|$ shells exist, which however, are inevitably stabilized at finite radial distance., Comment: 20 pages

It has been recently shown that nonlinear effects emerging at the time of the generation of the quasi-normal modes are necessary to model ringdowns from black hole mergers. In this note, we describe how nonlinerarities also arise when defining gauge-invariant tensor modes and in the calculation of the observable measured in the interferometers beyond linear order., Comment: 10 pages

It has been recently pointed out that nonlinear effects are necessary to model the ringdown stage of the gravitational waveform produced by the merger of two black holes giving rise to a remnant Kerr black hole. We show that this nonlinear behaviour is explained, both on the qualitative and quantitative level, by near-horizon symmetries of the Kerr black hole within the Kerr/CFT correspondence., Comment: 5 pages

We show that vanishing of the sigma-model beta-functions for the metric $g_{\mu\nu}$, antisymmetric tensor $B_{\mu\nu}$ and dilaton $\Phi$ of any string-theory model in $D$ dimensions at tree level can be obtained from a universal effective action, provided that the field combination $\sqrt{-g}e^{-2\Phi}$ is non-dynamical. The central-charge deficit term is omitted from the action and appears as an integration constant at the level of the field equations. The analysis is done at leading order in $\alpha'$, i.e. at the two-derivative level in the effective description. It can be extended to incorporate higher order string-loop corrections, Ramond-Ramond forms and moduli fields. In all cases, the non-dynamical field combination turns out to be $\sqrt{-g}\, U$, where $U$ is the effective potential. When certain fluxes are fixed and the moduli fields are stabilized, no cosmological term will arise in the action. Instead, the cosmological constant will appear as an integration constant as in unimodular modifications of general relativity., Comment: 1+23 pages

We show that the linear perturbations of any spin field in the near-zone limit of the Kerr black hole are identical to those of an AdS$_2$ black hole which enjoys the same basic properties of the Kerr black hole. Thanks to this identification, we calculate the spectrum of the quasinormal modes and the Love numbers of Kerr black holes using an AdS$_2$/CFT$_1$ correspondence and a group theoretical approach., Comment: 15 pages, LaTex file

The Standard Model Higgs potential becomes unstable at large Higgs field values where its quartic coupling becomes negative. While the tunneling lifetime of our current electroweak vacuum is comfortably longer than the age of the universe, quantum fluctuations during inflation might push the Higgs over the barrier, forming patches which might be lethal for our universe. We study the cosmological evolution of such regions and find that, at least in the thin wall approximation, they may be harmless as they collapse due to the backreaction of the Higgs itself. The presence of the Standard Model Higgs instability can provide a novel mechanism to end inflation and to reheat the universe through the evaporation of the black holes left over by the collapse of the Higgs bubbles. The bound on the Hubble rate during inflation may be therefore relaxed., Comment: 27 pages, 4 figures. v2: matching published version

We summarize the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with ESA and national space and research funding agencies., Comment: Summary of the Community Workshop on Cold Atoms in Space and corresponding Road-map: https://indico.cern.ch/event/1064855/

We study supersymmetry breaking from a complex linear superfield coupled to 4D N=1 supergravity. The theory has two classically decoupled vacua, one supersymmetric and one with broken and intrinsically non-linear supersymmetry. Depending on the values of the parameters the scalar potential can lead to no-scale Minkwoski or a stable de Sitter or anti-de Sitter vacuum. We also provide a dual description of the system in terms of a nilpotent chiral superfield and a standard chiral coupled to supergravity., Comment: 37 pages

We consider ${\cal N}=4$ conformal supergravity with an arbitrary holomorphic function of the complex scalar $S$ which parametrizes the $SU(1,1)/U(1)$ coset. Assuming non-vanishings vevs for $S$ and the scalars in a symmetric matrix $E_{ij}$ of the $\overline{\bf 10}$ of $SU(4)$ R-symmetry group, we determine the vacuum structure of the theory. We find that the possible vacua are classified by the number of zero eigenvalues of the scalar matrix and the spacetime is either Minkowski, de Sitter or anti-de Sitter. We determine the spectrum of the scalar fluctuations and we find that it contains tachyonic states which however can be removed by appropriate choice of the unspecified at the supergravity level holomorphic function. Finally, we also establish that $S$-supersymmetry is always broken whereas $Q$-supersymmetry exists only on flat Minkowski spacetime., Comment: 17 pages

We determine the inner product on the Hilbert space of wavefunctions of the universe by imposing the Hermiticity of the quantum Hamiltonian in the context of the minisuperspace model. The corresponding quantum probability density reproduces successfully the classical probability distribution in the $\hbar \to 0$ limit, for closed universes filled with a perfect fluid of index $w$. When $-1/3

The early history of the universe might be described by a topological phase followed by a standard second phase of Einstein gravity. To study this scenario in its full generality, we consider a four-manifold of Euclidean signature in the topological phase, which shares a common boundary with a corresponding manifold of Lorentzian signature in the Einstein phase. We find that the boundary should have vanishing extrinsic curvature, whereas the manifold in the topological phase should have zero Euler number. In addition, we show that the second phase must be characterized by an initial vanishing Weyl tensor and that the standard cosmological flatness problem is not automatically solved unless a conformal invariant boundary term is added. We also characterize the scalar perturbations in the standard Einstein phase. We show that they must contain an initial non-vanishing shear component inherited from the topological phase and we estimate the non-Gaussian parameters. Finally, we argue that the topological early universe cosmology shares common features of previous ideas, such as the so-called Weyl curvature hypothesis, the universe's creation out of nothing and the no-boundary proposal., Comment: 17 pages, 1 figure

We calculate the exact formation probability of primordial black holes generated during the collapse at horizon re-entry of large fluctuations produced during inflation, such as those ascribed to a period of ultra-slow-roll. We show that it interpolates between a Gaussian at small values of the average density contrast and a Cauchy probability distribution at large values. The corresponding abundance of primordial black holes may be larger than the Gaussian one by several orders of magnitude. The mass function is also shifted towards larger masses., Comment: 4 pages, 3 figures, minor additions, references added, matches published version

We derive a novel four-dimensional black hole with planar horizon that asymptotes to the linear dilaton background. The usual growth of its entanglement entropy before Page's time is established. After that, emergent islands modify to a large extent the entropy, which becomes finite and is saturated by its Bekenstein-Hawking value in accordance with the finiteness of the von Neumann entropy of eternal black holes. We demonstrate that viewed from the string frame, our solution is the two-dimensional Witten black hole with two additional free bosons. We generalize our findings by considering a general class of linear dilaton black hole solutions at a generic point along the $\sigma$-model renormalization group (RG) equations. For those, we observe that the entanglement entropy is "running" i.e. it is changing along the RG flow with respect to the two-dimensional worldsheet length scale. At any fixed moment before Page's time the aforementioned entropy increases towards the infrared (IR) domain, whereas the presence of islands leads the running entropy to decrease towards the IR at later times. Finally, we present a four-dimensional charged black hole that asymptotes to the linear dilaton background as well. We compute the associated entanglement entropy for the extremal case and we find that an island is needed in order for it to follow the Page curve., Comment: Journal version---discussion extended, typos corrected, references added

We study supergravity theories with supersymmetry intrinsically non-linearly realized supported only by four-form flux. We demonstrate that supersymmetry can be restored by the evaporation of the goldstino multiplet. Such procedure requires the existence of a super-extremal 2-brane, in accordance with the WGC, and suggests an imminent decay in de Sitter supergravity, leaving the system to relax in supersymmetric AdS after the transition. In particular, the same decay mechanism also implies that the KKLT de Sitter vacua are short-lived. Our findings thus provide an effective realization of KPV-type of decays within 4D supergravity and in this way may reconcile the nilpotent superfield constructions of de Sitter with some aspects of the swampland program., Comment: 32 pages, 4 figures, accepted in JHEP

Decoupling of heavy modes in effective low energy theory is one of the most fundamental concepts in physics. It tells us that modes must have a negligible effect on the physics of gravitational backgrounds with curvature radius larger than their wavelengths. Despite this, there exist claims that trans-Planckian modes put severe bound on the duration of inflation even when the Hubble parameter is negligible as compared to the Planck mass. If true, this would mean that inflation violates the principle of decoupling or at least requires its reformulation. We clarify the fundamental misconception on which these bounds are based and respectively refute them. Our conclusion is that inflation fully falls within the validity of a reliable effective field theory treatment and does not suffer from any spurious trans-Planckian problem., Comment: 5 pages

In these lectures we discuss N-extended conformal supergravity and its spectrum in four dimensions. These theories can be considered as the massless limit of Einstein-Weyl supergravity and by taking into account their enhanced gauge symmetries, we derive their massless spectrum, which in general contains a dipole-ghost graviton multiplet and an N-fold tripole-ghost gravitino multiplet., Comment: 15 pages, to appear in the Proceedings of the 2019 Erice Intl School of Subnuclear Physics, 57th Course

We consider four-dimensional quadratic gravity coupled to infinite towers of free massive scalar fields, Weyl fermions and vector bosons. We find that for specific numbers of towers, finite cosmological and Newton constants are induced in the 1-loop effective action. This is derived both in Adler's approach and by using the heat kernel method, which yield identical results. If the infinite number of massive states may be regarded as Kaluza--Klein modes arising from fields in higher dimensions, there are no Kaluza--Klein states associated with the four-dimensional graviton. Hence gravity is intrinsically four-dimensional.

In the first part of this paper we will work out a close and so far not yet noticed correspondence between the swampland approach in quantum gravity and geometric flow equations in general relativity, most notably the Ricci flow. We conjecture that following the gradient flow towards a fixed point, which is at infinite distance in the space of background metrics, is accompanied by an infinite tower of states in quantum gravity. In case of the Ricci flow, this conjecture is in accordance with the generalized distance and AdS distance conjectures, which were recently discussed in the literature, but it should also hold for more general background spaces. We argue that the entropy functionals of gradient flows provide a useful definition of the generalized distance in the space of background fields. In particular we give evidence that for the Ricci flow the distance $\Delta$ can be defined in terms of the mean scalar curvature of the manifold, $\Delta\sim\log \bar R$. For a more general gradient flow, the distance functional also depends on the string coupling constant. In the second part of the paper we will apply the generalized distance conjecture to gravity theories with higher curvature interactions, like higher derivative $R^2$ and $W^2$ terms. We will show that going to the weak coupling limit of the higher derivative terms corresponds to the infinite distance limit in metric space and hence this limit must be accompanied by an infinite tower of light states. For the case of the $R^2$ or $W^2$ couplings, this limit corresponds to the limit of a small cosmological constant or, respectively, to a light additional spin-two field in gravity. In general we see that the limit of small higher curvature couplings belongs to the swampland in quantum gravity, just like the limit of a small $U(1)$ gauge coupling belongs to the swampland as well., Comment: 36 pages; v2: references added; v3: version to appear in JHEP

Tensor non-Gaussianities are a key ingredient to test the symmetries and the presence of higher spin fields during the inflationary epoch. Indeed, the shape of the three point correlator of the graviton is totally fixed by the symmetries of the de Sitter stage and, in the case of parity conservation, gets contributions only from the ordinary gravity action plus a higher derivative term called the (Weyl)$^3$ action. We discuss current and future bounds on the three point tensor contribution from the (Weyl)$^3$ term using cosmic microwave background (CMB) bispectra. Our results indicate that forthcoming experiments, such as LiteBIRD, CMB-S4 and CORE, will detect the presence of the (Weyl)$^3$ term if $M_p^4 L^4 \sim 10^{17} r^{-4}$, where $L$ parametrizes the strength of the (Weyl)$^3$ term and $r$ is the tensor-to-scalar ratio, which corresponds to $L\gtrsim 3.2 \times 10^5 M_p^{-1}$, while the current upper limit is $M_p^4 L^4 = (1.1 \pm 4.0) \times 10^{19} r^{-4}$ (68%CL)., Comment: 8 pages, 2 figures; version matching publication in PRD

Primordial black holes could have been formed in the early universe from sufficiently large cosmological perturbations re-entering the horizon when the Universe is still radiation dominated. These originate from the spectrum of curvature perturbations generated during inflation at small-scales. Because of the non-linear relation between the curvature perturbation $\zeta$ and the overdensity $\delta\rho$, the formation of the primordial black holes is affected by intrinsic non-Gaussianity even though the curvature perturbation is Gaussian. We investigate the impact of this non-Gaussianity on the critical threshold $\delta_c$ which measures the excess of mass of the perturbation, finding a relative change with respect to the value obtained using a linear relation between $\zeta$ and $\delta\rho$, of a few percent. This shows that the value of the critical threshold is rather robust against non-linearities. The same holds also when cosmologically interesting values of local primordial non-Gaussianity are added to the curvature perturbation., Comment: 24 pages, 6 figures. This last updated version contains minor fine-tunings according to the published one

We discuss the connection between Weyl$^2$ supergravity and superstrings and further discuss holography between 4-dimensional, ${\cal N}=4$ superconformal Weyl$^2$ supergravity and ${\cal N}=8$, higher spin-four theory on $AdS_5$. The Weyl$^2$ plus Einstein supergravity theory is a special kind of a bimetric gravity theory and consists of a massless graviton multiplet plus an additional massive spin-two supermultiplet. Here, we argue that the additional spin-two field and its superpartners originate from massive excitations in the open string sector; just like the ${\cal N}=4$ super Yang-Mills gauge fields, they are localized on the world volume of D3-branes. The ghost structure of the Weyl action should be considered as an artifact of the truncation of the infinitely many higher derivative terms underlying the massive spin 2 action. In field theory, ${\cal N}=4$ Weyl$^2$ supergravity exhibits superconformal invariance in the limit of vanishing Planck mass. In string theory the additional spin-two fields become massless in the tensionless limit. Therefore low string scale scenarios with large extra dimensions provide (almost) superconformal field theories with almost massless open string spin-two fields. The full ${\cal N}=4$ scalar potential including the Yang-Mills matter multiplets is presented and the supersymmetric vacua of Einstein Supergravity are shown, as expected, to be vacua of massive Weyl supergravity. Other vacua are expected to exist which are not vacua of Einstein supergravity. Finally, we identify certain spin-four operators on the 4-dimensional boundary theory that could be the holographic duals of spin-four fields in the bulk., Comment: 33 pages, revised version with corrected typos and references added

We provide some comments about the constraints on the inflationary models inferred from the two Swampland criteria which have been recently proposed. In particular we argue that, in the absence of any knowledge about the origin of the adiabatic curvature perturbations, within the slow-roll single field models of inflation there is no tension between the swampland criteria and the current lower bound on the tensor-to-scalar ratio., Comment: 5 pages

In this paper we study the spectrum of all conformal, ${\cal N}$-extended supergravities (${\cal N}=1,2,3,4$) in four space-time dimensions. When these theories are obtained as massless limit of Einstein plus Weyl$^2$supergravity, the appropriate counting of the enhanced gauge symmetries allow us to derive the massless spectrum which consist of a dipole ghost graviton multiplet, a ${\cal N}$-fold tripole ghost gravitino, the third state belonging to a spin 3/2 multiplet and a residual vector multiplet present for non-maximal ${\cal N}<4$ theories. These theories are not expected to have a standard gravity holographic dual in five dimensions., Comment: 23 pages, Replaced version agrees with published version in JHEP

The presence of massive particles with spin during inflation induces distinct signatures on correlation functions of primordial curvature fluctuations. In particular, the bispectrum of primordial perturbations obtains an angular dependence determined by the spin of the particle, which can be used to set constraints on the presence of such particles. If these particles are long-lived on super-Hubble scales, as is the case for example for partially massless particles, their imprint on correlation functions of curvature perturbations would be unsuppressed. In this paper, we make a forecast for how well such angular dependence can be constrained by the upcoming EUCLID spectroscopic survey via the measurement of galaxy bispectrum., Comment: v2 is equivalent to the version accepted by the Phys.Rev. D. A new plot and some additional discussions added

We consider primordial black hole (PBH) production in inflationary $\alpha$-attractors. We discuss two classes of models, namely models with a minimal polynomial superpotential as well as modulated chaotic ones that admit PBHs. We find that a significant amplification of the curvature power spectrum ${\cal P_R}$ can be realized in this class of models with a moderate tuning of the potential parameters. We consistently examine the PBH formation during radiation and additionally during reheating eras where the background pressure is negligible. It is shown that basic features of the curvature power spectrum are explicitly related with the postinflationary cosmic evolution and that the PBH mass and abundance expressions are accordingly modified. PBHs in the mass range $10^{-16}-10^{-14} \, M_{\odot}$ can form with a cosmologically relevant abundance for a power spectrum peak ${\cal P_R} \sim 10^{-2}$ and large reheating temperature and, furthermore, for a moderate peak ${\cal P_R} \sim 10^{-5}$ and reheating temperature $T_\text{rh}\sim 10^7$ GeV, characteristic of the position of the power spectrum peak. Regarding the CMB observables, the $\alpha$-attractor models utilized here to generate PBH in the low-mass region predict in general a smaller $n_s$ and larger $r$ and $\alpha_s$ parameter values compared to the conventional inflationary $\alpha$-attractor models., Comment: 34 pages, 12 figures with 33 plots. Minor corrections. References added. In this version there are updated parameters for our inflationary models in accordance with the Planck 2018 results. Journal version

We discuss a new interaction for chiral models in four-dimensional ${\cal N}=1$ supergavity. It contains a new arbitrary function in addition to the K\"ahler potential and superpotential. Its features include linearly realized off-shell supersymmetry, K\"ahler-Weyl invariance and broken supersymmetry. The corresponding scalar potential is augmented by the arbitrary function which allows freedom in constructing low-energy phenomenological models and inflationary models rooted in supergravity., Comment: 27 pages, published version

Primordial black holes as dark matter may be generated in single-field models of inflation thanks to the enhancement at small scales of the comoving curvature perturbation. This mechanism requires leaving the slow-roll phase to enter a non-attractor phase during which the inflaton travels across a plateau and its velocity drops down exponentially. We argue that quantum diffusion has a significant impact on the primordial black hole mass fraction making the classical standard prediction not trustable., Comment: 25+12 pages, 12 figures. v3: Appendix added with comments in response to arXiv:1807.09057

Inflation may provide a suitable collider to probe physics at very high energies. In this paper we investigate the impact on the CMB bispectrum of higher spin fields which are long-lived on super-Hubble scales, e.g. partially massless higher spin fields. We show that distinctive statistical anisotropic signals on the CMB three-point correlator are induced and we investigate their detectability., Comment: 11 pages, 5 figures

If there exist higher-spin particles during inflation which are light compared to the Hubble rate, they may leave distinct statistical anisotropic imprints on the correlators involving scalar and graviton fluctuations. We characterise such signatures using the dS/CFT$_3$ correspondence and the operator product expansion techniques. In particular, we obtain generic results for the case of partially massless higher-spin states., Comment: 21 pages, 2 figures, v2: matching published version

We show that the minimal D = 5, N = 2 gauged supergravity set-up may encode naturally the recently proposed clockwork mechanism. The minimal embedding requires one vector multiplet in addition to the supergravity multiplet and the clockwork scalar is identified with the scalar in the vector multiplet. The scalar has a two-parameter potential and it can accommodate the clockwork, the Randall-Sundrum and a no-scale model with a flat potential, depending on the values of the parameters. The continuous clockwork background breaks half of the original supersymmetries, leaving a D = 4, N = 1 theory on the boundaries. We also show that the generated hierarchy by the clockwork is not exponential but rather power law. The reason is that four-dimensional Planck scale has a power-law dependence on the compactification radius, whereas the corresponding KK spectrum depends on the logarithm of the latter., Comment: 20 pages

Ultra-light axions have sparked attention because their tiny mass $m\sim 10^{-22}$ eV, which leads to a Kiloparsec-scale de Broglie wavelength comparable to the size of dwarf galaxy, could alleviate the so-called small-scale crisis of massive cold dark matter (CDM) candidates.However, recent analyses of the Lyman-$\alpha$ forest power spectrum set a tight lower bound on their mass of $m\gtrsim 10^{-21}$ eV which makes them much less relevant from an astrophysical point of view. An important caveat to these numerical studies is that they do not take into account attractive self-interactions among ultra-light axions, which can counteract the quantum "pressure" induced by the strong delocalization of the particles. In this work, we show that even a tiny attractive interaction among ultra-light axions can have a significant impact on the stability of cosmic structures at low redshift. After a brief review of known results about solitons in the absence of gravity, we discuss the stability of filamentary and pancake-like solutions when quantum pressure, attractive interactions and gravity are present. The analysis based on one degree of freedom, namely the breathing mode, reveals that pancakes are stable, while filaments are unstable if the mass per unit length is larger than a critical value. However, we show that pancakes are unstable against transverse perturbations. We expect this to be true for halos and filaments as well. Instabilities driven by the breathing mode will not be seen in the low column density Lyman-$\alpha$ forest unless the axion decay constant is extremely small, $f\lesssim 10^{13}$ GeV. Notwithstanding, axion solitonic cores could leave a detectable signature in the Lyman-$\alpha$ forest if the normalization of the unknown axion core - filament mass relation is $\sim 100$ larger than it is for spherical halos., Comment: 20 pages, 3 figures. Comments welcome (v2) Improved discussion of the Lyman-alpha forest; factors of 2 fixed; references added. Accepted to PRD

Primordial inflation may represent the most powerful collider to test high-energy physics models. In this paper we study the impact on the inflationary power spectrum of the comoving curvature perturbation in the specific model where massive higher spin fields are rendered effectively massless during a de Sitter epoch through suitable couplings to the inflaton field. In particular, we show that such fields with spin $s$ induce a distinctive statistical anisotropic signal on the power spectrum, in such a way that not only the usual $g_{2M}$-statistical anisotropy coefficients, but also higher-order ones (i.e., $g_{4M}$, $g_{6M}$, $\cdots$, $g_{(2s-2)M}$ and $g_{(2s) M}$) are nonvanishing. We examine their imprints in the cosmic microwave background and galaxy power spectra. Our Fisher matrix forecasts indicate that the detectability of $g_{LM}$ depends very weakly on $L$: all coefficients could be detected in near future if their magnitudes are bigger than about $10^{-3}$., Comment: 10 pages, 3 figures; version matching publication in PRD

Cosmological perturbations of massive higher-spin fields are generated during inflation, but they decay on scales larger than the Hubble radius as a consequence of the Higuchi bound. By introducing suitable couplings to the inflaton field, we show that one can obtain statistical correlators of massive higher-spin fields which remain constant or decay very slowly outside the Hubble radius. This opens up the possibility of new observational signatures from inflation., Comment: 22 pages

According to the dS/CFT correspondence, correlators of fields generated during a primordial de Sitter phase are constrained by three-dimensional conformal invariance. Using the properties of radially quantized conformal field theories and the operator-state correspondence, we glean information on some points. The Higuchi bound on the masses of spin-s states in de Sitter is a direct consequence of reflection positivity in radially quantized CFT$_3$ and the fact that scaling dimensions of operators are energies of states. The partial massless states appearing in de Sitter correspond from the boundary CFT$_3$ perspective to boundary states with highest weight for the conformal group. We discuss inflationary consistency relations and the role of asymptotic symmetries which transform asymptotic vacua to new physically inequivalent vacua by generating long perturbation modes. We show that on the CFT$_3$ side, asymptotic symmetries have a nice quantum mechanics interpretation. For instance, acting with the asymptotic dilation symmetry corresponds to evolving states forward (or backward) in "time" and the charge generating the asymptotic symmetry transformation is the Hamiltonian itself. Finally, we investigate the symmetries of anisotropic inflation and show that correlators of four-dimensional free scalar fields can be reproduced in the dual picture by considering an isotropic three-dimensional boundary enjoying dilation symmetry, but with a nonvanishing vacuum expectation value of the boundary stress-energy momentum tensor., Comment: 41 pages, 4 figures

We investigate the recently proposed clockwork mechanism delivering light degrees of freedom with suppressed interactions and show, with various examples, that it can be efficiently implemented in inflationary scenarios to generate flat inflaton potentials and small density perturbations without fine-tunings. We also study the clockwork graviton in de Sitter and, interestingly, we find that the corresponding clockwork charge is site-dependent. As a consequence, the amount of tensor modes is generically suppressed with respect to the standard cases where the clockwork set-up is not adopted. This point can be made a virtue in resurrecting models of inflation which were supposed to be ruled out because of the excessive amount of tensor modes from inflation., Comment: 19 pages, 1 fugure

We consider the minimal three-form ${\cal N}=1$ supergravity coupled to nilpotent three-form chiral superfields. The supersymmetry breaking is sourced by the three-forms of the chiral multiplets, while the value of the gravitino mass is controlled by the three-form of the supergravity multiplet. The three-forms can nucleate membranes which scan both the supersymmetry breaking scale and the gravitino mass. The peculiar supergravity feature that the cosmological constant is the sum of a positive contribution from the supersymmetry breaking scale and a negative contribution from the gravitino mass makes the cosmological constant jump. This can lead to a phenomenologically allowed small value of the cosmological constant even though the supersymmetry breaking scale and the gravitino mass are dynamically large., Comment: 18 pages, 2 figures, JHEP version, citations added