Fri·Jun 16, 2023Friday·June 16, 2023

1. 01*

   Sum rules for the Gravitational Form Factors using light-front dressed quark state

   Jai More🇮🇳 · Asmita Mukherjee🇮🇳 · Sreeraj Nair🇨🇳 · Sudeep Saha🇮🇳

   We consider a light-front dressed quark state, per se, instead of a proton state, we consider a simple composite spin-1/2 state of a quark dressed with a gluon. This perturbative model incorporates gluonic degrees of freedom, which enable us to evaluate the gravitational form factors (GFFs) of the quark as well as the gluon in this model \cite{More:2021stk, More:2023pcy}. We employ the Hamiltonian framework and choose the light-front gauge $A^{+}=0$. We calculate the four GFFs and corroborate the sum rules that GFFs satisfy. The GFF $D$ is attributed to information like pressure, shear, and energy distributions. We analyze some of these distributions for a dressed quark state at one loop in QCD.

   hep-phhep-thFew Body Syst.(2023)·2 citations
2. 02*

   Top Secrets: Long-Lived ALPs in Top Production

   Lovisa Rygaard🇩🇪 · Jeremi Niedziela🇩🇪 · Ruth Schäfer🇩🇪 · Sebastian Bruggisser🇩🇪 · Juliette Alimena🇩🇪 · Susanne Westhoff🇩🇪 · Freya Blekman🇩🇪

   We investigate the discovery potential for long-lived particles produced in association with a top-antitop quark pair at the (High-Luminosity) LHC. Compared to inclusive searches for a displaced vertex, top-associated signals offer new trigger options and an extra handle to suppress background. We design a search strategy for a displaced di-muon vertex in the tracking detectors, in association with a reconstructed top-antitop pair. For axion-like particles with masses above the di-muon threshold, we find that the (High-Luminosity) LHC can probe effective top-quark couplings as small as $|c_{tt}|/f_a=0.03(0.002)/$TeV and proper decay lengths as long as $20(300)$ m, assuming a cross section of $1$ fb, with data corresponding to an integrated luminosity of 150 fb${}^{-1}$ (3 ab${}^{-1}$). Our predictions suggest that searches for top-associated displaced di-muons will explore new terrain in the current sensitivity gap between searches for prompt di-muons and missing energy.

   hep-phhep-exJHEP(2023)·21 citations
3. 03*

   Probing Lepton Number Violation: A Comprehensive Survey of Dimension-7 SMEFT

   Kåre Fridell🇯🇵 · Lukáš Gráf🇺🇸 · Julia Harz🇩🇪 · Chandan Hati🇩🇪

   Observation of lepton number violation would represent a groundbreaking discovery with profound consequences for fundamental physics and as such, it has motivated an extensive experimental program searching for neutrinoless double beta decay. However, the violation of lepton number can be also tested by a variety of other observables. We focus on the possibilities of probing this fundamental symmetry within the framework of the Standard Model Effective Field Theory (SMEFT) beyond the minimal dimension-5. Specifically, we study the bounds on $\Delta L=2$ dimension-7 effective operators beyond the electron flavor imposed by all relevant low-energy observables and confront them with derived high-energy collider limits. We also discuss how the synergy of the analyzed multi-frontier observables can play a crucial role in distinguishing among different dimension-7 SMEFT operators.

   hep-phJHEP(2024)·33 citations
4. 04*

   Higher Order Corrections to the Effective Field Theory of Low-energy Axions

   Bryan Cordero-Patino🇪🇨 · Álvaro Duenas-Vidal🇪🇨 · Jorge Segovia🇪🇸

   Dark matter (DM) can be composed of a collection of axions, or axion-like particles (ALPs), whose existence is due to the spontaneous breaking of the Peccei-Quinn $U(1)$ symmetry which is the most compelling solution of the strong $CP$-problem of Quantum Chromodynamics (QCD). Axions must be spin-$0$ particles with very small masses and extremely weak interactions with themselves as well as with the particles that constitute the Standard Model. In general, the physics of axions is detailed by a quantum field theory of a real scalar field, $\varphi$. Nevertheless, it is more convenient to implement a non-relativistic effective field theory with a complex scalar field, $\psi$, to characterize the mentioned axions in the low-energy regime. A possible application of this equivalent description is to study the collapse of cold dark matter into more complex structures. There have been a few derivations of effective Lagrangians for the complex field $\psi$; resulting to be all equivalent after a nonlocal-space transformation between $\varphi$ and $\psi$ was found, and some other corrections were introduced. Our contribution herein is to further provide higher order corrections, in particular, we compute the effective field theory Lagrangian up to order $({\psi }^{\ast }\psi {)}^5$, incorporating also the fast-oscillating field fluctuations into the dominant slowly-varying non-relativistic field.

   hep-phhep-exhep-thnucl-ex+1Symmetry(2023)·1 citation
5. 05*

   Particle interaction strengths modified by magnetic fields

   Gabriella Piccinelli🇲🇽 · Angel Sanchez🇲🇽 · Jorge Jaber-Urquiza🇲🇽

   Magnetic fields are everywhere in the Universe and in our everyday life and many processes are affected by their presence, generating a rich phenomenology that depends also on other possible external agents. We review here some results, both from our workgroup and from other research groups, about the effect of magnetic fields on particles interaction processes, focusing mainly on recent results, but without losing sight on early seminal works on this topic. A vast assortment of physical situations and of analytical and numerical approaches can be found in the literature in this subject, making the comparison between them not straightforward. Our aim is to focus attention on differences and similarities between the different situations and approaches, looking for a systematization scheme that could be predictive, once the role played by each physical ingredient could be understood. The main purpose of this work is to find some physical explanations of the ongoing processes.

   hep-phAstron.Nachr.(2023)·0 citations
6. 06*

   Discovery potential for axions in Hamburg

   A. Ringwald🇩🇪

   We review the motivation for axions, discuss benchmark axion models, and report on the ongoing and planned axion experiments in Hamburg and their discovery potential.

   hep-phastro-ph.HEastro-ph.SRhep-ex1 citation
7. 07*

   A simplest modular $S_3$ model for leptons

   Davide Meloni🇮🇹 · Matteo Parriciatu🇮🇹

   We present minimalist constructions for lepton masses and mixing based on flavour symmetry under the modular group ${\Gamma }_N$ of lowest level $N=2$. As opposed to the only existing model of ${\Gamma }_2\cong S_3$ formulated in a SUSY framework, the only non-SM field is the modulus $\tau$, and a generalised CP symmetry is implemented. Charged-leptons masses are reproduced through symmetry arguments, without requiring fine-tuning of the free parameters. As a result, all lepton observables (masses and mixing) are reproduced within $1\sigma$ experimental range using a minimum of nine free real parameters (including the real and imaginary parts of the modulus). A normal ordering for the neutrino masses is predicted. We also obtain predictions for the CP violating phases: the Dirac CP phase is predicted around $1.6\pi$, the Majorana phases lie in narrow regions near $\pm \pi$. The sum of neutrino masses is within the current bound at $\sim 0.09\text{eV}$. Furthermore, we provide predictions for the neutrinoless double beta decay and tritium decay effective masses, around $20\text{meV}$. Given the reduced number of free input parameters as compared to the existing literature on modular $S_3$, this work renews interest for a unified predictive model of quark-lepton sectors based on ${\Gamma }_2\cong S_3$.

   hep-phhep-thJHEP(2023)·35 citations
8. 08*

   Explanation of the Hints for a 95 GeV Higgs Boson within a 2-Higgs Doublet Model

   Alexander Belyaev (1) (2)🇬🇧 · Rachid Benbrik (3)🇲🇦 · Mohammed Boukidi (3)🇲🇦 · Manimala Chakraborti (1)🇬🇧 · Stefano Moretti (1) (4)🇬🇧 · Souad Semlali (1) (2) ((1) School of Physics and Astronomy, University of Southampton, United Kingdom, (2) Particle Physics Department, Rutherford Appleton Laboratory, United Kingdom, (3) Polydisciplinary Faculty, Laboratory of Fundamental and Applied Physics, Cadi Ayyad University, Sidi Bouzid, Safi, Morocco, (4) Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden)🇬🇧

   We suggest an explanation for and explore the consequences of the excess around 95 GeV in the di-photon and di-tau invariant mass distributions recently reported by the CMS collaboration at the Large Hadron Collider (LHC), together with the discrepancy that has long been observed at the Large Electron-Positron (LEP) collider in the $b\bar{b}$ invariant mass. Interestingly, the most recent findings announced by the ATLAS collaboration do not contradict, or even support, these intriguing observations. Their search in the di-photon final state similarly reveals an excess of events within the same mass range, albeit with a bit lower significance, thereby corroborating and somewhat reinforcing the observations made by CMS. We demonstrate that the lightest CP-even Higgs boson in the general 2-Higgs Doublet Model (2HDM) Type-III can explain simultaneously the observed excesses at approximately 1.3 $\sigma$ C.L. while satisfying up-to-date theoretical and experimental constraints. Moreover, the 2HDM Type-III predicts an excess in the $pp\to t\bar{t}{H}_{\mathrm{SM}}$ production channel of the 125 GeV Higgs boson, $H_{\mathrm{SM}}$. This effect is caused by a up to 12\% enhancement of the $H_{\mathrm{SM}}tt$ Yukawa coupling in comparison to that predicted by the Standard Model. Such an effect can be tested at the High Luminosity LHC (HL-LHC), which can either discover or exclude the scenario we suggest. This unique characteristic of the 2HDM Type-III makes this scenario with the 95 GeV resonance very attractive for further theoretical and experimental investigations at the (HL-)LHC and future colliders.

   hep-phhep-exJHEP(2024)·50 citations
9. 09*

   Scheme and gauge dependence of QCD fixed points at five loops

   J.A. Gracey🇬🇧 · R.H. Mason🇬🇧 · Thomas A. Ryttov🇩🇰 · R.M. Simms🇬🇧

   We analyse the fixed points of QCD at high loop order in a variety of renormalization schemes and gauges across the conformal window. We observe that in the minimal momentum subtraction scheme solutions for the Banks-Zaks fixed point persist for values of Nf below that of the MSbar scheme in the canonical linear covariant gauge. By treating the parameter of the linear covariant gauge as a second coupling constant we confirm the existence of a second Banks-Zaks twin critical point, which is infrared stable, to five loops. Moreover a similar and parallel infrared stable fixed point is present in the Curci-Ferrari and maximal abelian gauges which persists in different schemes including kinematic ones. We verify that with the increased available loop order critical exponent estimates show an improvement in convergence and agreement in the various schemes.

   hep-phPRD(2023)·12 citations
10. 10*

    Universality of energy-momentum response in kinetic theories

    Xiaojian Du🇪🇸 · Stephan Ochsenfeld🇩🇪 · Sören Schlichting🇩🇪

    We study the response of the energy-momentum tensor in several kinetic theories, from the simple relaxation time approximation (RTA) to Quantum Chromodynamics (QCD). Irrespective of the differences in microscopic properties, we find a remarkable degree of universality in the response functions from conformal theories. We find that the response to scalar perturbations in kinetic theory can be effectively described by a pair of one hydrodynamic sound mode and one non-hydrodynamic mode. We find that even beyond the range of validity of hydrodynamics, the energy-momentum response in position space can be effectively described by one single mode with non-trivial dispersion relation and residue.

    hep-phnucl-thPLB(2023)·13 citations
11. 11*

    One-loop Effective Action up to Dimension Eight: Integrating out Heavy Scalar(s)

    Upalaparna Banerjee🇮🇳 · Joydeep Chakrabortty🇮🇳 · Shakeel Ur Rahaman🇮🇳 · Kaanapuli Ramkumar🇮🇳

    We present the complete one-loop effective action up to dimension eight after integrating out degenerate scalars using the Heat-Kernel method. The result is provided without assuming any specific form of either UV or low energy theories, i.e., universal. In this paper, we consider the effects of only heavy scalar propagators in the loops. We also verify part of the results using the covariant diagram technique.

    hep-phhep-thEur.Phys.J.Plus(2024)·32 citations
12. 12*

    Explaining the $B_{d,s}\to K^{(\ast )}{\bar{K}}^{(\ast )}$ non-leptonic puzzle and charged-current $B$-anomalies via scalar leptoquarks

    Javier M. Lizana🇨🇭 · Joaquim Matias🇪🇸 · Ben A. Stefanek🇨🇭

    We present a model based on $S_1$ scalar leptoquarks to solve the tension observed in the recently proposed non-leptonic optimized observables $L_{K^{\ast }{\bar{K}}^{\ast }}$ and $L_{K\bar{K}}$. These observables are constructed as ratios of U-spin related decays based on $B_{d,s}^0\to K^{(\ast )0}{\bar{K}}^{(\ast )0}$. The model gives a one-loop contribution to the Wilson coefficient of the chromomagnetic dipole operator needed to explain the tension in both non-leptonic observables, while naturally avoiding large contributions to the corresponding electromagnetic dipoles. The necessary chiral enhancement comes from an $O(1)$ Yukawa coupling with a TeV-scale right-handed neutrino running in the loop. We endow the model with a $U(2)$ flavor symmetry, necessary to protect light-family flavor observables that otherwise would be in tension. Furthermore, we show that the same $S_1$ scalar leptoquark is capable of simultaneously explaining the hints of lepton flavor universality violation observed in charged-current $B$-decays. The model therefore provides a potential link between two puzzles in $B$-physics and TeV-scale neutrino mass generation. Finally, the combined explanation of the $B$-physics puzzles unavoidably results in an enhancement of $\mathcal{B}(B\to K\nu \bar{\nu })$, yielding a value close to present bounds.

    hep-phhep-exJHEP(2023)·19 citations
13. 13*

    Theory of heavy-quarks contribution to the quark-gluon plasma viscosity

    Alessio Zaccone🇮🇹

    The shear viscosity of quark gluon plasma is customarily estimated in the literature using kinetic theory, which, however, is well known to break down for dense interacting systems. Here we propose an alternative theoretical approach based on recent advances in the physics of dense interacting liquid-like systems, which is valid for strongly-interacting and arbitrarily dense relativistic systems. With this approach, the viscosity of strongly interacting dense heavy-quarks plasma is evaluated analytically, at the level of special relativity. For QGP well above the confinement temperature, the theory predicts that the viscosity increases with the cube of temperature, in agreement with evidence.

    hep-phcond-mat.stat-mechhep-latnucl-thNPB(2024)·5 citations
14. 14*

    QCD resummation of dijet azimuthal decorrelations in pp and pA collisions

    Mei-Sen Gao🇨🇳 · Zhong-Bo Kang🇺🇸 · Ding Yu Shao🇨🇳 · John Terry🇺🇸 · Cheng Zhang🇨🇳

    We study the azimuthal angular decorrelations of dijet production in both proton-proton (pp) and proton-nucleus (pA) collisions. By utilizing soft-collinear effective theory, we establish the factorization and resummation formalism at the next-to-leading logarithmic accuracy for the azimuthal angular decorrelations in the back-to-back limit in pp collisions. We propose an approach where the nuclear modifications to dijet production in pA collisions are accounted for in the nuclear modified transverse momentum dependent parton distribution functions (nTMDPDFs), which contain both collinear and transverse dynamics. This approach naturally generalizes the well-established formalism related to the nuclear modified collinear parton distribution functions (nPDFs). We demonstrate strong consistency between our methodology and the CMS measurements in both pp and pA collisions, and make predictions for dijet production in the forward rapidity region in pA collisions at LHC kinematics and for mid-rapidity kinematics at sPHENIX. Throughout this paper, we focus on the application of this formalism to a simultaneous fit to both collinear and transverse momentum dependent contributions to the transverse momentum dependent distributions.

    hep-phhep-exnucl-exnucl-thJHEP(2023)·18 citations
15. 15*

    Study of B^{0}_{s} \rightarrow \ TT(a_{2}(1320),K^{*}_{2}(1430),f_{2}(1270),f^{'}_{2}(1525)) in the perturbative QCD approach

    Jing Dai🇨🇳 · Xian-Qiao Yu🇨🇳

    In the present study, the calculations of two-body decays B^{0}_{s} \rightarrow \ TT [ T denotes tensor mesons, a_{2}(1320), K^{*}_{2}(1430), f_{2}(1270), f^{'}_{2}(1525)] in the perturbative QCD approach are presented. The ensuing predictions encompass branching ratios, polarization fractions, and direct CP violations, all elucidated in comprehensive detail. It is discerned that (1) for pure annihilation decay, the longitudinal polarization is around 90.0\%, whereas the transverse polarizations manifest comparatively diminutive magnitudes. (2) The direct CP asymmetry is directly proportional to the interference between the tree and penguin contributions. For most of the decays investigated within this discourse, the direct CP asymmetry remains modest in magnitude. (3) There are precisely six distinct categories of Feynman diagrams for B^{0}_{s} \rightarrow \ TT , because the tensor mesons cannot be produced through the (V \pm A) currents or (S \pm P) density, thereby prohibiting factorizable emission diagrams. The nonfactorizable and annihilation contributions are ascertained to be pivotal in these decay modes. The calculated branching ratios of our calculation for B^{0}_{s} \rightarrow \ TT are at the order of 10^{-6} and 10^{-7}, which can be tested in the LHCb and Belle II experiments. (4) Mixing exists for the f_{2}(1270) and f^{'}_{2}(1525), just as the \eta and \eta^{'} mixing, the branching ratios about the mixing angle \theta are given in this work. However, it is different from f_{1}(1285)-f_{1}(1420), the mixing angle is notably small, thereby resulting in only marginal alterations in the decay branching ratios.

    hep-phPRD(2024)·2 citations
16. 16*

    SMEFT Restrictions On Exclusive $b\to u\ell \nu$ Decays

    Admir Greljo🇨🇭 · Jakub Salko🇨🇭 · Aleks Smolkovič🇨🇭 · Peter Stangl🇨🇭

    Exclusive semileptonic $b$ hadron decays ($b\to u\ell \nu$) serve as a sandbox for probing strong and electroweak interactions and for extracting the CKM element $V_{ub}$. Instead, this work investigates their underexplored potential to reveal new short-distance physics. Utilizing SMEFT as a conduit to chart territory beyond the SM, we demonstrate that substantive new physics contributions in $b\to u\ell \nu$ are necessarily linked to correlated effects in rare neutral-current $b$ decays, neutral $B$ meson mixing or high-mass Drell-Yan tails. We find that measurements of the latter processes strongly restrict the allowed deviations in the former. A complete set of tree-level mediators, originating from a perturbative ultraviolet model and matching at dimension 6, is thoroughly explored to support this assertion. As a showcase application, we examine the feasibility of a new physics interpretation of the recent tension in exclusive $|V_{ub}|$ extraction from $B\to V\ell \nu$ where $V=(\rho ,\omega )$.

    hep-phhep-exhep-latJHEP(2023)·22 citations
17. 17*

    Post-inflationary production of particle Dark Matter: Hilltop and Coleman-Weinberg inflation

    Anish Ghoshal🇵🇱 · Maxim Yu. Khlopov🇷🇺 · Zygmunt Lalak🇵🇱 · Shiladitya Porey🇷🇺

    We investigate the production of non-thermal dark matter (DM), $\chi$, during post-inflationary reheating era. For inflation, we consider two slow roll single field inflationary scenarios - generalized version of Hilltop (GH) inflation, and Coleman-Weinberg (CW) inflation. Using a set of benchmark values that comply with the current constraints from Cosmic Microwave Background Radiation (CMBR) data for each inflationary model, we explored the parameter space involving mass of dark matter particles, $m_{\chi }$, and coupling between inflaton and $\chi$, $y_{\chi }$. For these benchmarks, we find that tensor-to-scalar ratio $r$ can be as small as $2.69\times 10^{-6}$ for GH and $1.91\times 10^{-3}$ for CW inflation, both well inside $1-\sigma$ contour on scalar spectral index versus $r$ plane from Planck2018+BICEP3+KeckArray2018 dataset, and testable by future cosmic microwave background (CMB) observations e.g. Simons Observatory. For the production of $\chi$ from the inflaton decay satisfying CMB and other cosmological bounds and successfully explaining total cold dark matter density of the present universe, we find that $y_{\chi }$ should be within this range $\mathcal{O}\left(10^{-4}\right)\gtrsim y_{\chi }\gtrsim \mathcal{O}\left(10^{-20}\right)$ for both inflationary scenarios. We also show that, even for the same inflationary scenario, the allowed parameter space on reheating temperature versus $m_{\chi }$ plane alters with inflationary parameters including scalar spectral index, $r$, and energy scale of inflation.

    hep-phastro-ph.COPRD(2024)·5 citations
18. 18*

    Heating Galaxy Clusters with Interacting Dark Matter

    Yutaro Shoji🇮🇱 · Eric Kuflik🇮🇱 · Yuval Birnboim🇮🇱 · Nicholas C. Stone🇮🇱

    The overcooling of cool core clusters is a persistent puzzle in the astrophysics of galaxy clusters. We propose that it may naturally be resolved via interactions between the baryons of the intracluster medium (ICM) and its dark matter (DM). DM-baryon interactions can inject heat into the ICM to offset bremmstrahlung cooling, but these interactions are also strongly constrained by existing experiments and astrophysical observations. We survey existing constraints and combine these with the energetic needs of an observed sample of cool core clusters. We find that a robust parameter space exists for baryon-DM scattering solutions to the cooling flow problem, provided that only a sub-component of DM interacts strongly with the baryons. Interestingly, baryon-DM scattering is a thermally stable heating source so long as the baryon temperature is greater than $1/3-1/2$ the DM temperature, a condition that seems to be satisfied observationally.

    ↳ astro-ph.COastro-ph.GAhep-phMNRAS(2024)·5 citations
19. 19*

    A cosmic-ray database update: CRDB v4.1

    D. Maurin🇫🇷 · M. Ahlers🇩🇰 · H. Dembinski🇩🇪 · A. Haungs🇩🇪 · P.-S. Mangeard🇺🇸 · F. Melot🇫🇷 · P. Mertsch🇩🇪 · D. Wochele🇩🇪 · J. Wochele🇩🇪

    The cosmic-ray database, CRDB, has been gathering cosmic-ray data for the community since 2013. We present a new release, CRDB v4.1, providing many new quantities and data sets, with several improvements made on the code and web interface, and with new visualisation tools. CRDB relies on the mysql database management system, jquery and tsorter libraries for queries and sorting, and PHP web pages and AJAX protocol for displays. A REST interface enables user queries from command line or scripts. A new (pip-installable) CRDB python library is developed and extensive jupyter notebook examples are provided. This release contains cosmic-ray dipole anisotropy data, high-energy $\bar{p}/p$ upper limits, some unpublished LEE and AESOP lepton time series, many more ultra-high energy data, and a few missing old data sets. It also includes high-precision data from the last three years, in particular the hundreds of thousands AMS-02 and PAMELA data time series (time-dependent plots are now enabled). All these data are shown in a gallery of plots, which can be easily reproduced from the public notebook examples. CRDB contains 316,126 data points from 504 publications, in 4111 sub-experiments from 131 experiments.

    ↳ astro-ph.HEastro-ph.IMhep-exhep-phEPJC(2023)·45 citations
20. 20*

    Non-Gaussian transverse momentum fluctuations from impact parameter fluctuations

    Rupam Samanta🇵🇱 · João Paulo Picchetti🇧🇷 · Matthew Luzum🇧🇷 · Jean-Yves Ollitrault🇫🇷

    The transverse momentum per particle, $[p_t]$, fluctuates event by event in ultrarelativistic nucleus-nucleus collisions, for a given multiplicity. These fluctuations are small and approximately Gaussian, but a non-zero skewness has been predicted on the basis of hydrodynamic calculations, and seen experimentally. We argue that the mechanism driving the skewness is that, if the system thermalizes, the mean transverse momentum increases with impact parameter for a fixed collision multiplicity. We postulate that fluctuations are Gaussian at fixed impact parameter, and that non-Gaussianities solely result from impact parameter fluctuations. Using recent data on the variance of $[p_t]$ fluctuations, we make quantitative predictions for their skewness and kurtosis as a function of the collision multiplicity. We predict in particular a spectacular increase of the skewness below the knee of the multiplicity distribution, followed by a fast decrease.

    ↳ nucl-thhep-exhep-phnucl-exPRC(2023)·24 citations
21. 21*

    Does NANOGrav observe a dark sector phase transition?

    Torsten Bringmann🇳🇴 · Paul Frederik Depta🇩🇪 · Thomas Konstandin🇩🇪 · Kai Schmidt-Hoberg🇩🇪 · Carlo Tasillo🇩🇪

    Gravitational waves from a first-order cosmological phase transition, at temperatures at the MeV-scale, would arguably be the most exciting explanation of the common red spectrum reported by the NANOGrav collaboration, not the least because this would be direct evidence of physics beyond the standard model. Here we perform a detailed analysis of whether such an interpretation is consistent with constraints on the released energy deriving from big bang nucleosynthesis and the cosmic microwave background. We find that a phase transition in a completely secluded dark sector is strongly disfavoured with respect to the more conventional astrophysical explanation of the putative gravitational wave signal in terms of supermassive black hole binaries. On the other hand, a phase transition in a dark sector that subsequently decays, before the time of neutrino decoupling, remains an intriguing possibility to explain the data. From the model-building perspective, such an option is easily satisfied for couplings with the visible sector that are small enough to evade current collider and astrophysical constraints. The first indication that could eventually corroborate such an interpretation, once the observed common red spectrum is confirmed as a nHz gravitational wave background, could be the spectral tilt of the signal. In fact, the current data already show a very slight preference for a spectrum that is softer than what is expected from the leading astrophysical explanation.

    ↳ astro-ph.COhep-phJCAP(2023)·118 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.