Search

The decays of the $B$ meson into vector mesons, observed at the LHCb experiment, provide an ideal laboratory to investigate particle physics phenomena with quantum information theory methods. In this article, we focus on the decays yielding a pair of $\it{\Phi}$ mesons to investigate the presence of entanglement in the spin correlations of the system and quantify the amount of Bell inequality violation it entails. Our results show that the present LHCb data allows access to entanglement and to the Bell inequality violation with a significance exceeding the 5$\sigma$ threshold in both the cases. This demonstrates that the strong and electroweak interactions responsible for the $B$ meson decay act as a source of entanglement and the quantum mechanics nature of high-energy phenomena. Particular attention is paid to the assessment of loopholes: deficiencies in the experimental setup which could invalidate the results of the Bell test., Comment: review article to appear in Symmetry MDPI, 16 pages

Generalized uncertainty principles are effective changes to the Heisenberg uncertainty principle that emerge in several quantum gravity models. In the present letter, we study the consequences that two classes of these modifications yield on the physics of neutrinos. Besides analyzing the change in the oscillation probabilities that the generalized uncertainty principles entail, we assess their impact on the neutrino coherence length and their possible interpretation as nonstandard neutrino interactions. Constraints cast by present and planned neutrino experiments on the generalized uncertainty principles parameters are also derived., Comment: 9 pages, matches published version

The study of entanglement in particle physics has been gathering pace in the past few years. It is a new field that is providing important results about the possibility of detecting entanglement and testing Bell inequality at colliders for final states as diverse as top-quark, $\tau$-lepton pairs and $\Lambda$-baryons, massive gauge bosons and vector mesons. In this review, after presenting definitions, tools and basic results that are necessary for understanding these developments, we summarize the main findings -- as published by the beginning of year 2024 -- including analyses of experimental data in $B$ meson decays and top-quark pair production. We include a detailed discussion of the results for both qubit and qutrits systems, that is, final states containing spin one-half and spin one particles. Entanglement has also been proposed as a new tool to constrain new particles and fields beyond the Standard Model and we introduce the reader to this promising feature as well., Comment: Review article, published version in Progress in Particle and Nuclear Physics

A novel first order action principle has been proposed as the possible foundation for a more fundamental theory of General Relativity and the Standard Model. It is shown in this article that the proposal consistently incorporates gravity and matter fields, and guides to a new and robust path towards unification of fundamental interactions., Comment: 6 pages and references

We consider a scale-invariant inverse seesaw model with dynamical breaking of gauge symmetry and lepton number. In some regions of the parameter space, the Majoron - the pseudo-Goldstone of lepton number breaking - is a viable dark matter candidate. The bound on the Majoron decay rate implies a very large dilaton vacuum expectation value, which also results in a suppression of other dark matter couplings. Because of that, the observed dark matter relic abundance can only be matched via the freeze-in mechanism. The scalar field which gives mass to heavy neutrinos can play the role of the inflaton, resulting in a tensor-to-scalar ratio $r \lesssim 0.01$ for metric inflation and $r \lesssim 0.21$ for Palatini gravity., Comment: 31 pages, 3 figures, version published in JHEP, typos corrected

We explore the phenomenology of quantum entanglement at collider experiments by computing the polarization density matrix of processes yielding two massive gauge bosons. After reviewing the formalism, we detail observables suitable to test the presence of entanglement and quantum correlations in the di-boson system. The implied violation of Bell inequalities can be observed with future data at the LHC in the decays of the Higgs boson to $Z$ boson pairs., Comment: Contribution to the 2023 Electroweak session of the 57th Rencontres de Moriond

We write down the teleparallel equivalent to Hassan-Rosen bigravity, which is written using a torsionful but curvature-free connection. The theories only differ by a boundary term. The equivalence was proven, both by using perturbation theory and Hamiltonian analysis. It is further shown how one can construct novel bigravity theories within the teleparallel framework. Some of those are analyzed through perturbation theory, and it is found that all of the considered novel bigravity theories suffer from pathologies. In particular, it is found that a construction with two copies of new general relativity leads to ghostly degrees of freedom which are not present in the single tetrad teleparallel corresponding theory. We demonstrate how the teleparallel framework allows to easily create theories with derivative interaction. However, it is shown through perturbation theory that the simplest model is not viable. Furthermore, we demonstrate some steps in the Hamiltonian analysis of teleparallel bigravity with two copies of new general relativity and some toy models. The results rule out some of the novel teleparallel bigravity theories, but also demonstrate techniques in perturbation theory and Hamiltonian analysis which could be further used for more profound theories in the future., Comment: 32 pages, 1 figure, matches published version

The inert doublet model is a well-motivated extension of the Standard Model that contains a dark matter candidate and modifies the dynamics of the electroweak symmetry breaking. In order to detail its phenomenology, we perform a comprehensive study of cosmic phase transitions and gravitational wave signals implied by the framework, accounting for the latest results of collider experiments. We require the neutral inert scalar to constitute, at least, a subdominant part of the observed dark matter abundance. While most of the phase transitions proceed through a single step, we identify regions of the parameter space where the electroweak vacuum is reached after multiple phase transitions. The resulting gravitational wave spectrum is generally dominated by single-step transitions and, in part of the parameter space, falls within the reach of future gravitational wave detectors such as LISA, BBO or DECIGO. We find that direct detection experiments efficiently probe the part of parameter space associated with multi-step phase transitions, which remain unconstrained only in the Higgs resonance region testable with future monojet searches. The implications of the new determination of the $W$ boson mass are also discussed., Comment: 27 pages, 17 figures. Version accepted by JCAP

We consider the classically scale invariant Higgs-dilaton model of dynamical symmetry breaking extended with an extra scalar field that plays the role of dark matter. The Higgs boson is light near a critical boundary between different symmetry breaking phases, where quantum corrections beyond the usual Gildener-Weinberg approximation become relevant. This implies a tighter connection between dark matter and Higgs phenomenology. The model has only three free parameters, yet it allows for the observed relic abundance of dark matter while respecting all constraints. The direct detection cross section mediated by the Higgs boson is determined by the dark matter mass alone and is testable at future experiments., Comment: 9 pages, 4 figures; for a webinar presentation of the paper see https://www.youtube.com/watch?v=ZTIdhPiI7hk

The standard description of particles and fundamental interactions is crucially based on a regular metric background. In the language of differential geometry, this dependence is encoded into the action via Hodge star dualization. As a result, the conventional forms of the scalar and Yang-Mills actions break down in a pregeometric regime where the metric is degenerate. This suggests the use of first order formalism, where the metric may emerge from more fundamental constituents and the theory can be consistently extended to the pregeometric phase. We systematically explore different realizations and interpretations of first order formalism, finding that a fundamental vector or spinor substructure brings about continuum magnetization and polarization as integration constants. This effect is analogous to the description of the cosmological dark sector in a recent self-dual formulation of gravity, and the similar form obtained for the first order Yang-Mills theory suggests new paths toward unification., Comment: 33 pages, no figures

The recently proposed multi-phase criticality principle in Coleman-Weinberg models can provide a new explanation for the hierarchy between the electroweak and new physics scales. When applied to the Standard Model, a Higgs boson as light as the pseudo-Goldstone boson of broken scale invariance occurs. The suppressed mixing between the two light fields still carries information about the large scale of symmetry breaking, albeit up to logarithmic corrections. In this work we probe this scenario with the present LHC data and assess the impact of future lepton and hadron colliders. Our results show that the multi-phase criticality can easily explain the apparent absence of new physics at the energy scales tested in current experiments., Comment: 9 pages, 4 figures

We study the evolution of light spectator fields in an asymmetric polynomial potential. During inflation, stochastic fluctuations displace the spectator field from the global minimum of its potential, populating the false vacuum state and thereby allowing for the formation of false vacuum bubbles. By using a lattice simulation, we show that these bubbles begin to contract once they re-enter the horizon and, if sufficiently large, collapse into black holes. This process generally results in the formation of primordial black holes, which, due to the specific shape of their mass function, are constrained to yield at most 1% of the total dark matter abundance. However, the resulting population can source gravitational wave signals observable at the LIGO-Virgo experiments, provide seeds for supermassive black holes or cause a transient matter-dominated phase in the early Universe., Comment: 25 pages, 8 figures

We explore the electroweak vacuum stability in the framework of a recently proposed paradigm for the origin of Yukawa couplings. These arise as low energy effective couplings radiatively generated by portal interactions with a hidden, or dark, sector at the one-loop level. Possible tree-level Yukawa couplings are forbidden by a new underlying symmetry, assumed to be spontaneously broken by the vacuum expectation value of a new scalar field above the electroweak scale. As a consequence, the top Yukawa interaction ceases to behave as a local operator at energies above the new sector scale and, therefore, cannot contribute to the running of the quartic Higgs coupling at higher energies. By studying two complementary scenarios, we explicitly show that the framework can achieve the stability of the electroweak vacuum without particular tuning of parameters. The proposed mechanism requires the existence of a dark sector and new portal messenger scalar interactions that, connecting the Standard Model to the dark sector fields, could be tested at the LHC and future collider experiments., Comment: 27 pages, 4 figures, new results and one figure added, improved text, revised version as published one

Extensions to the Standard Model that use strictly off-shell degrees of freedom - the fakeons - allow for new measurable interactions at energy scales usually precluded by the constraints that target the on-shell propagation of new particles. Here we employ the interactions between a new fake scalar doublet and the muon to explain the recent Fermilab measurement of its anomalous magnetic moment. Remarkably, unlike in the case of usual particles, the experimental result can be matched for fakeon masses below the electroweak scale without contradicting the stringent precision data and collider bounds on new light degrees of freedom. Our analysis, therefore, demonstrates that the fakeon approach offers unexpected viable possibilities to model new physics naturally at low scales., Comment: 7 pages, 5 figures, PRD version

We introduce a new way of modeling the physics beyond the Standard Model by considering fake, strictly off-shell degrees of freedom: the fakeons. To demonstrate the approach and exemplify its reach, we re-analyze the phenomenology of the Inert Doublet Model under the assumption that the second doublet is a fakeon. Remarkably, the fake doublet avoids the most stringent $Z$-pole constraints regardless of the chosen mass scale, thereby allowing for the presence of new effects well below the electroweak scale. Furthermore, the absence of on-shell propagation prevents fakeons from inducing missing energy signatures in collider experiments. The distinguishing features of the model appear at the loop level, where fakeons modify the Higgs boson $h\to\gamma\gamma$ decay width and the Higgs trilinear coupling. The running of Standard Model parameters proceeds as in the usual Inert Doublet Model case. Therefore, the fake doublet can also ensure the stability of the Standard Model vacuum. Our work shows that fakeons are a valid alternative to the usual tools of particle physics model building, with the potential to shape a new paradigm, where the significance of the existing experimental constraints towards new physics must necessarily be reconsidered., Comment: 12 pages, 7 figures, version accepted by JHEP

We show that the observed primordial perturbations can be entirely sourced by a light spectator scalar field with a quartic potential, akin to the Higgs boson, provided that the field is sufficiently displaced from vacuum during inflation. The framework relies on the indirect modulation of reheating, which is implemented without any direct coupling between the spectator field and the inflaton and does not require non-renormalisable interactions. The scenario gives rise to local non-Gaussianity with $f_{\rm NL}\simeq 5$ as the typical signal. As an example model where the indirect modulation mechanism is realised for the Higgs boson, we study the Standard Model extended with right-handed neutrinos. For the Standard Model running we find, however, that the scenario analysed does not seem to produce the observed perturbation., Comment: Figures modified, analysis extended, references added, matches published version

The Coleman-Weinberg mechanism can realise different phases of dynamical symmetry breaking. In each phase a combination of scalars, corresponding to the pseudo-Goldstone boson of scale invariance, has a loop-suppressed mass. We show that additional scalars, beyond the pseudo-Goldstone bosons, can become light at critical points in the parameter space where two different phases co-exist. We present a minimal implementation of the mechanism in multi-scalar models, detailing how loop-suppressed masses and mixings can be computed. We discuss realisations of the resulting multi-phase criticality principle and its relevance to the case of the Higgs boson., Comment: 10 pages, 2 figures, version accepted in PLB

We propose a new formalism to analyse the extremum structure of scale-invariant effective potentials. The problem is stated in a compact matrix form, used to derive general expressions for the stationary point equation and the mass matrix of a multi-field RG-improved effective potential. Our method improves on (but is not limited to) the Gildener-Weinberg approximation and identifies a set of conditions that signal the presence of a radiative minimum. When the conditions are satisfied at different scales, or in different subspaces of the field space, the effective potential has more than one radiative minimum. We illustrate the method through simple examples and study in detail a Standard-Model-like scenario where the potential admits two radiative minima. Whereas we mostly concentrate on biquadratic potentials, our results carry over to the general case by using tensor algebra., Comment: 43 pages, 6 figures, published version

We consider the boosted dark matter solution of the XENON1T excess to constrain the framework through loop-generated processes. The interaction of the boosted dark matter component, which sources the signal, effectively couples the cold dark matter background to the electrons, making it potentially visible in the electron recoil searches. Similarly, once the radiative corrections due to the Standard Model are taken into account, dark matter also scatters on quarks and becomes observable in nuclear recoil measurements. By analysing these processes, we find that the current direct detection constraints exclude the upper mass range selected by the anomaly if the boosted component is generated through dark matter annihilation., Comment: 6 pages, 3 figures

We demonstrate that light spectator fields can source sizeable CMB anisotropies through modulated reheating even in the absence of direct couplings to the inflaton. The effect arises when the phase space of the inflaton decay is modulated by the spectator which generates masses for the decay products. We call the mechanism \textit{indirect modulation} and show that it can source perturbations even four orders of magnitude larger than the observed. Importantly, the indirect mechanism is present in the Standard Model extended with right-handed neutrinos. For a minimally coupled Higgs boson this leads to a novel lower bound on the quartic coupling and constrains the neutrino Yukawas below unity., Comment: discussion updated, references added

We put forward the framework of simplified leptoquark models: simple extensions of the Standard Model that serve as benchmarks to test the interactions of leptons with new colored degrees of freedom considered, for instance, in leptoquark or grand unification models. As a first application of the scheme, we analyze the power of precision lepton observables by computing gauge invariant two-loop radiative corrections to the lepton-photon vertex, generated here by Yukawa interactions between the lepton and new colored degrees of freedom. The result, detailed in explicit expressions for the involved form factors, improves on the literature for the higher loop order considered and highlights the existence of regions in the parameter space of the model where two-loop corrections cannot be neglected., Comment: 17 pages, 12 figures. Ancillary file attached: Diags.m v2: Minor changes to text and references updated. Version accepted in PRD

We provide a dynamical mechanism for the generation of the Cabibbo-Kobayashi-Maskawa matrix in the context of a recently proposed model of flavor. The framework, based on the paradigm that Yukawa couplings are effective low energy couplings generated radiatively by dark sector interactions, is here extended to include a new scalar field which plays the role of a {\it dark flavon}. Being singlet under the Standard Model gauge group but charged under the $U(1)$ symmetry of the dark sector, this particle sources new two- and three-loop diagrams that result in off-diagonal Yukawa interactions, thereby providing a simple explanation for the observed structure of the CKM matrix. By using an effective parametrization of these new loop contributions, we show that the CKM matrix elements can be correctly reproduced for perturbative values of the involved couplings. We outline the rich phenomenology predicted by the scenario and detail its implications for the LHC and future collider experiments.

A theory of gravity is deduced from the axioms of the premetric program. The starting point is the conservation of energy and momenta, and the equivalence of gravitation and inertia. The latter is what leads to the framework of the so called purified gravity. The local and linear constitutive relation has 14 components when it is assumed to be metrical, but the compatibility of the constitutive relation with an action principle fixes uniquely the theory of Coincident General Relativity. The premetric formalism of purified gravity has a direct analogy with massive electromagnetism, the Planck mass corresponding to the Proca mass of the gauge boson. The metric emerges as a Stueckelberg field, and the graviton as a Goldstone boson of the broken symmetry., Comment: 32 pages, 2 figures, 2 tables

We observe that biquadratic potentials admit non-trivial flat directions when the determinant of the quartic coupling matrix of the scalar fields vanishes. This consideration suggests a new approach to the problem of finding flat directions in scale-invariant theories, noticeably simplifying the study of scalar potentials involving many fields. The method generalizes to arbitrary quartic potentials by requiring that the hyperdeterminant of the tensor of scalar couplings be zero. We demonstrate our approach with detailed examples pertaining to common scalar extensions of the Standard Model., Comment: 6 pages, 1 figure

We propose a new framework for the observed flavor hierarchy and mixing based on left-right supersymmetry. The model contains the most minimal Higgs sector consisting only of gauge doublets which forbid the standard model Yukawa couplings. New mediator fields then connect the left- and right-chiral fermion sectors and result in effective tree level Yukawa couplings for the third generation charged fermions. The remaining fermions, including all neutrinos, acquire effective Yukawa couplings sourced by the supersymmetry breaking sector at loop level. We predict new TeV range scalars, as well as heavier fermions and vector bosons, that can be discovered at the LHC and future colliders., Comment: 21 pages, 7 figures

Scalar theories can account for the current $R_{D^{(*)}}$ measurements through a vector operator $\bar{c}_L \gamma_{\mu} b_L\,\bar{\tau}_L \gamma^{\mu}\nu_L$ induced at the loop level. Once the vector contribution is considered on top of a subdominant tree-level scalar component, the predicted value of $R_{D^{(*)}}$ falls within the $1\sigma$ region indicated by the experiments. We explicitly demonstrate this claim in the framework of a three Higgs doublet model extended with GeV scale right-handed neutrinos, by matching the anomalous signal for perturbative values of the involved couplings and respecting the bounds from complementary flavour physics measurements. Remarkably, we furthermore show that the proposed framework can be employed to simultaneously explain also the present $R_{K^{(*)}}$ measurement, as well as the deviation in $\epsilon'/\epsilon$ currently being debated in the literature. These results are obtained by considering the contribution of relatively light right-handed neutrinos which are fundamental in mediating the processes behind the anomalous signals. In this way our findings reveal a new possible connection that links the flavour anomalies to the phenomenology of extended Higgs sector and neutrino physics., Comment: 18 pages, 11 figures

Within classically conformal models, the spontaneous breaking of scale invariance is usually associated to a strong first order phase transition that results in a gravitational wave background within the reach of future space-based interferometers. In this paper we study the case of the classically conformal gauged B-L model, analysing the impact of this minimal extension of the Standard Model on the dynamics of the electroweak symmetry breaking and derive its gravitational wave signature. Particular attention is paid to the problem of vacuum stability and to the role of the QCD phase transition, which we prove responsible for concluding the symmetry breaking transition in part of the considered parameter space. Finally, we calculate the gravitational wave signal emitted in the process, finding that a large part of the parameter space of the model can be probed by LISA., Comment: 11 pages, 6 figures. Minor changes to match the published version

We show that a minimal extension of the Standard Model including a new complex scalar field can explain inflation and the observed effective number of neutrinos. The real part of the singlet plays the role of the inflaton field, while the Goldstone boson emerging from the spontaneous symmetry breaking of a global $U(1)$ symmetry contributes to dark radiation and increases the effective number of neutrino species by $0.3$ over the Standard Model value. After detailing the phenomenology of the model, we find that the predicted inflationary observables are in agreement with the current bounds, once the dark radiation component is allowed, both within the metric and Palatini formulation of non-minimally coupled gravity., Comment: 10 pages, 1 figure, 1 table, matches the published version

Various theories beyond the Standard Model predict the existence of heavy resonances decaying to Higgs (H) boson pairs. In order to maximize the sensitivity of searches for such resonances, it is important that experimental analyses cover a variety of decay modes. The decay of H boson pairs to four $\tau$ leptons (HH$ \to \tau\tau\tau\tau$) has not been discussed in the literature so far. This decay mode provides a small branching fraction, but also comparatively low backgrounds. We present an algorithm for the reconstruction of the mass of the H boson pair in events in which the H boson pair decays via HH$ \to \tau\tau\tau\tau$ and the $\tau$ leptons subsequently decay into electrons, muons, or hadrons. The algorithm achieves a resolution of $7$-$22\%$ relative to the mass of the H boson pair, depending on the mass of the resonance., Comment: 14 pages, 3 figures

It is shown that a spontaneously-broken gauge theory of the Lorentz group contains Ashtekar's chiral formulation of General Relativity accompanied by dust. From this perspective, gravity is described entirely by a connection $\omega$ valued in the Lie algebra of the complexified Lorentz group and a Lorentz-charged scalar field $\tau$. The model is "pre-geometric" in the sense that the spacetime metric may be constructed only in the symmetry-broken regime. We speculate on the extent to which this dust may account for dark matter and on the behaviour of the theory in regimes where the symmetry is not broken., Comment: v2 with minor edits, as published

The recent observation of the 21-cm absorption signal by the EDGES experiment provides a new observational window into the dynamics of the young Universe. Based on this result, we constrain the properties of ALPs and excited dark matter via the energy injections into the gaseous medium that these models produce. In particular, we derive bounds that outperform the present constraints for energy injections in the 10.2 eV to 50 keV range by analysing the intensity of Lyman-$\alpha$ photons and the electron emissivity produced by ionising radiation. Our results also show that once the standard temperature of the soft radiation background is assumed, the explanations of the observed 3.5 keV photon signal within the considered dark matter model are excluded at 95\% confidence level., Comment: 7 pages, 3 figures

Recent measurements of semileptonic B-meson decays seemingly imply violations of lepton flavor universality beyond the Standard Model predictions. With three-level explanations based on extended Higgs sectors being strongly challenged by the measurements of the $B_c^-$ lifetime, new theories invoking leptoquark or vector fields appear as the only feasible answer. However, in this work we show that simple scalar extensions of the Standard Model still offer a possible solution to the $B$ physics puzzle, owing to sizeable loop-level corrections which mimic the effects of new vector contributions. Considering a simplified model characterised by a charged and a neutral scalar particle, we verify the compatibility of the observed $R_{D^{(*)}}$ signal with the relevant collider bounds. We also study an embedding of the simplified model into a three-Higgs-doublet framework, and investigate its main phenomenological constraints., Comment: 15 pages, 12 figures. v2: References updated, larger captions for most of the plots. Version to appear on PRD

We study possible effects of a dark matter (DM) core on the maximum mass of a neutron star (NS), on the mass-radius relation and on the NS tidal deformability parameter $\Lambda$. We show that all these quantities would in general be reduced in the presence of a DM core. In particular, our calculations indicate that the presence of a DM core with a mass fraction $\sim 5\%$ could affect significantly the interpretation of these NS data as constraints on the nuclear equation of state (EOS), potentially excluding some EOS models on the basis of the measured mass of PSR J0348+0432, while allowing other EOS models to become consistent with the LIGO/Virgo upper limit on $\Lambda$. Specific scenarios for generating such DM cores are explored in an Appendix., Comment: 7 pages, 4 figures; minor changes to match the published version

The EDGES experiment has recently measured an anomalous global 21-cm spectrum due to hydrogen absorptions at redshifts of about $z\sim 17$. Model independently, the unusually low temperature of baryons probed by this observable sets strong constraints on any physical process that transfers energy into the baryonic environment at such redshifts. Here we make use of the 21-cm spectrum to derive bounds on the energy injection due to a possible population of ${\cal O}(1-100) M_\odot$ primordial black holes, which induce a wide spectrum of radiation during the accretion of the surrounding gas. After calculating the total radiative intensity of a primordial black hole population, we estimate the amount of heat and ionisations produced in the baryonic gas and compute the resulting thermal history of the Universe with a modified version of RECFAST code. Finally, by imposing that the temperature of the gas at $z\sim 17$ does not exceed the indications of EDGES, we constrain the possible abundance of primordial black holes. Depending on uncertainties related to the accretion model, we find that ${\cal O}(10) M_\odot$ primordial black holes can only contribute to a fraction $f_{\rm PBH}<(1-10^{-3})$ of the total dark matter abundance., Comment: 7 pages, 5 figures, PRD accepted

The recently claimed anomaly in the measurement of the 21 cm hydrogen absorption signal by EDGES at $z\sim 17$, if cosmological, requires the existence of new physics. The possible attempts to resolve the anomaly rely on either (i) cooling the hydrogen gas via new dark matter-hydrogen interactions or (ii) modifying the soft photon background beyond the standard CMB one, as possibly suggested also by the ARCADE~2 excess. We argue that solutions belonging to the first class are generally in tension with cosmological dark matter probes once simple dark sector models are considered. Therefore, we propose soft photon emission by light dark matter as a natural solution to the 21 cm anomaly, studying a few realizations of this scenario. We find that the signal singles out a photophilic dark matter candidate characterised by an enhanced collective decay mechanism, such as axion mini-clusters., Comment: 7 pages, 2 figures

In constant-roll inflation, the scalar field that drives the accelerated expansion of the Universe is rolling down its potential at a constant rate. Within this framework, we highlight the relations between the Hubble slow-roll parameters and the potential ones, studying in detail the case of a single-field Coleman-Weinberg model characterised by a non-minimal coupling of the inflaton to gravity. With respect to the exact constant-roll predictions, we find that assuming an approximate slow-roll behaviour yields a difference of $\Delta r = 0.001$ in the tensor-to-scalar ratio prediction. Such a discrepancy is in principle testable by future satellite missions. As for the scalar spectral index $n_s$, we find that the existing 2-$\sigma$ bound constrains the value of the non-minimal coupling to $\xi_\phi \sim 0.29-0.31$ in the model under consideration., Comment: 2 figures and a few comments added, matches version published in JCAP

We perform frequentist and Bayesian statistical analyses of Higgs- and Z-portal models of dark matter particles with spin 0, 1/2 and 1. Our analyses incorporate data from direct detection and indirect detection experiments, as well as LHC searches for monojet and monophoton events, and we also analyze the potential impacts of future direct detection experiments. We find acceptable regions of the parameter spaces for Higgs-portal models with real scalar, neutral vector, Majorana or Dirac fermion dark matter particles, and Z-portal models with Majorana or Dirac fermion dark matter particles. In many of these cases, there are interesting prospects for discovering dark matter particles in Higgs or Z decays, as well as dark matter particles weighing $\gtrsim 100$ GeV. Negative results from planned direct detection experiments would still allow acceptable regions for Higgs- and Z-portal models with Majorana or Dirac fermion dark matter particles., Comment: 9 figures, 8 tables, 34 pages. v3: closely matches published version

Motivated by the recent detection of the gravitational wave signal emitted by a binary neutron star merger, we analyse the possible impact of dark matter on such signals. We show that dark matter cores in merging neutron stars may yield an observable supplementary peak in the gravitational wave power spectral density following the merger, which could be distinguished from the features produced by the neutron components., Comment: 5 pages, 4 figures; minor changes to match the published version

We show that the coherent oscillations of a spin-2 field from bimetric theory can easily account for the observed dark matter abundance. We obtain the equation of motion for the field in a cosmological setting and discuss in detail the phenomenology of the model. The framework is testable in precision measurements of oscillating electric charge in atomic clocks, using atomic spectroscopy and in dedicated resonant mass detectors as well as in axion-like-particles experiments, which therefore provide a new window to probe and test gravity itself. We also comment on possible multimetric extensions of the framework that straightforwardly implement the clockwork mechanism for gravity., Comment: 5 pages + references

Within the framework of scalar-tensor theories, we study the conditions that allow single field inflation dynamics on small cosmological scales to significantly differ from that of the large scales probed by the observations of cosmic microwave background. The resulting single field double inflation scenario is characterised by two consequent inflation eras, usually separated by a period where the slow-roll approximation fails. At large field values the dynamics of the inflaton is dominated by the interplay between its non-minimal coupling to gravity and the radiative corrections to the inflaton self-coupling. For small field values the potential is, instead, dominated by a polynomial that results in a hilltop inflation. Without relying on the slow-roll approximation, which is invalidated by the appearance of the intermediate stage, we propose a concrete model that matches the current measurements of inflationary observables and employs the freedom granted by the framework on small cosmological scales to give rise to a sizeable population of primordial black holes generated by large curvature fluctuations. We find that these features generally require a potential with a local minimum. We show that the associated primordial black hole mass function is only approximately lognormal., Comment: 14 pages, 2 figures. Added references, corrected typos. To appear in JCAP

There has been a steady interest in flavor anomalies and their global fits as ideal probes of new physics. If the anomalies are real, one promising explanation is a new $Z'$ gauge boson with flavor-changing coupling to bottom and strange quarks and a flavor-conserving coupling to muons and, possibly, electrons. We point out that direct production of such a $Z'$, emerging from the collision of $b$ and $s$ quarks, may offer a complementary window into these phenomena because collider searches already provide competitive constraints. On top of that, we analyse the same $Z'$ scenario in relation to another long-standing discrepancy between theory and experiment that concerns the anomalous magnetic moment of the muon. By scanning the allowed $Z'$ coupling strengths in the low-mass region, we assess the compatibility of the signals from LHCb with the $Z'$ searches in the high energy LHC data and the measurements of the anomalous magnetic moment of the involved leptons. We also argue that observations of the latter can break the degeneracy pattern in the Wilson coefficients $C_9$ and $C_{10}$ presented by LHCb data. The $Z'$ model we consider is compatible with the new measurement of $R_{K^*}$, therefore it can potentially account for the long-standing deviations observed in $B$-physics., Comment: 13 pages, 5 figures. Missing factors corrected in eqs. 2.7-2.9 with slight updates in fig. 2

Thermal corrections in classically conformal models typically induce a strong first-order electroweak phase transition, thereby resulting in a stochastic gravitational wave background that could be detectable at gravitational wave observatories. After reviewing the basics of classically conformal scenarios, in this paper we investigate the phase transition dynamics in a thermal environment and the related gravitational wave phenomenology within the framework of scalar conformal extensions of the Standard Model. We find that minimal extensions involving only one additional scalar field struggle to reproduce the correct phase transition dynamics once thermal corrections are accounted for. Next-to-minimal models, instead, yield the desired electroweak symmetry breaking and typically result in a very strong gravitational wave signal., Comment: 9 pages and 7 figures. Minor changes to match the published version

Coy dark matter is an effective scheme in which a fermionic dark matter candidate interacts with the Standard Model fermions via a pseudoscalar mediator. This simple setup avoids the strong constraints posed by direct detection experiments in a natural way and explains, on top of the observed dark matter relic abundance, the spatially extended gamma-ray excess recently detected at the Galactic Center. In this Letter we study the phenomenology of coy dark matter accounting for a novel signature of the model: the diphoton annihilation signal induced by the Standard Model fermions at the loop level. By challenging the model with the observations of spheroidal dwarf satellite galaxies and the results of gamma-ray line searches obtained by the Fermi LAT experiment, we assess its compatibility with the measured dark matter relic abundance and the Galactic Center excesses. We show that despite the gamma-ray line constraint rules out a significant fraction of the considered parameter space, the region connected to the observed Galactic Center excess remains currently viable. Nevertheless, we find that next-generation experiments such as DAMPE, HERD and GAMMA-400 have the potential to probe exhaustively this elusive scenario., Comment: 9 pages, 3 figures; references and a footnote added; a latex error corrected

Seemingly unrelated models of inflation that originate from different physical setups yield, in some cases, identical predictions for the currently constrained inflationary observables. In order to classify the available models, we propose to express the slow-roll parameters and the relevant observables in terms of frame and reparametrisation invariant quantities. The adopted invariant formalism makes manifest the redundancy that afflicts the current description of inflation dynamics and offers a straightforward way to identify classes of models which yield identical phenomenology. In this Letter we offer a step-to-step recipe to recast every single field inflationary model in the proposed formalism, detailing also the procedure to compute inflationary observables in terms of frame and reparametrisation invariant quantities. We hope that our results become the cornerstone of a new categorisation of viable inflationary models and open the way to a deeper understanding of the inflation mechanism., Comment: 7 pages; Added a paragraph on new directions in model building and modified the adopted notation. Matches the version to appear on PRL

We reanalyse the prospects for upcoming Ultra-High Energy Cosmic Ray experiments in connection with the phenomenology of Super-heavy Dark Matter. We identify a set of observables well suited to reveal a possible anisotropy in the High Energy Cosmic Ray flux induced by the decays of these particles, and quantify their performance via Monte Carlo simulations that mimic the outcome of near-future and next-generation experiments. The spherical and circular dipoles are able to tell isotropic and anisotropic fluxes apart at a confidence level as large as $4\sigma$ or $5\sigma$, depending on the Dark Matter profile. The forward-to-backward flux ratio yields a comparable result for relatively large opening angles of about 40~deg, but it is less performing once a very large number of events is considered. We also find that an actual experiment employing these observables and collecting 300~events at 60~EeV would have a $50\%$ chance of excluding isotropy against Super-heavy Dark Matter at a significance of at least $3\sigma$, Comment: 15 pages + appendix + 10 figures

We revisit a recent solution to the flavor hierarchy problem based on the paradigm that Yukawa couplings are, rather than fundamental constants, effective low energy couplings radiatively generated by interactions in a hidden sector of the theory. In the present paper we show that the setup required by this scenario can be set by gauge invariance alone, provided that the Standard Model gauge group be extended to the left-right symmetric group of $SU(2)_L\times SU(2)_R\times U(1)_Y$. The simplest scheme in which Yukawa couplings are forbidden at the tree-level organises the right-handed fermions into doublets and presents an additional Higgs $SU(2)_R$ doublet, responsible for the spontaneous breaking of the $SU(2)_R$ gauge sector. The flavor and chiral symmetry breaking induced by the $SU(2)_R$ breaking is transferred at the one-loop level to the Standard Model via the dynamics of the hidden sector, which effectively regulates the spread of the effective Yukawa couplings. The emerging left-right symmetric framework recovers additional appealing features typical of these models, allowing for instance to identify the hypercharges of the involved fermions with their $B-L$ charges and offering a straightforward solution to the strong CP problem. The scheme gives rise to a distinguishing phenomenology that potentially can be tested at the LHC and future colliders through the same interactions that result in the radiative generation of Yukawa couplings, as well as by exploiting the properties of the additional $SU(2)_R$ Higgs doublet., Comment: matches the version published in PRD containing an added appendix

We provide further details on a recent proposal addressing the nature of the dark sectors in cosmology and demonstrate that all current observations related to Dark Matter can be explained by the presence of a heavy spin-2 particle. Massive spin-2 fields and their gravitational interactions are uniquely described by ghost-free bimetric theory, which is a minimal and natural extension of General Relativity. In this setup, the largeness of the physical Planck mass is naturally related to extremely weak couplings of the heavy spin-2 field to baryonic matter and therefore explains the absence of signals in experiments dedicated to Dark Matter searches. It also ensures the phenomenological viability of our model as we confirm by comparing it with cosmological and local tests of gravity. At the same time, the spin-2 field possesses standard gravitational interactions and it decays universally into all Standard Model fields but not into massless gravitons. Matching the measured DM abundance together with the requirement of stability constrains the spin-2 mass to be in the 1 to 100 TeV range., Comment: Latex, 46 pages, 4 figures. Matches published version