The 50 most-cited articles in Physics Letters B, 2021

We propose a novel model in the framework of f(Q) gravity, which is a gravitational modification class arising from the incorporation of non-metricity. The model has General Relativity as a particular limit, it has the same number of free parameters to those of ΛCDM, however at a cosmological framework it gives rise to a scenario that does not have ΛCDM as a limit. Nevertheless, confrontation with observations at both background and perturbation levels, namely with Supernovae type Ia (SNIa), Baryonic Acoustic Oscillations (BAO), cosmic chronometers (CC), and Redshift Space Distortion (RSD) data, reveals that the scenario, according to AIC, BIC and DIC information criteria, is in some datasets slightly preferred comparing to ΛCDM cosmology, although in all cases the two models are statistically indiscriminate. Finally, the model does not exhibit early dark energy features, and thus it immediately passes BBN constraints, while the variation of the effective Newton's constant lies well inside the observational bounds.

The holographic cut-off, in the formalism of generalized holographic dark energy (HDE), is generalized to depend on LIR=LIR(Lp,L˙p,L¨p,⋯,Lf,L˙f,⋯,a), where Lp and Lf are the particle horizon and future horizon respectively, and a is the scale factor of the universe. Based on such formalism, we showed that the Barrow entropic dark energy (DE) model is equivalent to the generalized HDE where the respective holographic cut-off is determined by two ways – (1) in terms of particle horizon and its derivative and (2) in terms of future horizon and its derivative. Interestingly, such cut-off turns out to depend up-to first order derivative of Lp or Lf respectively. Such equivalence between the Barrow entropic dark energy and the generalized HDE is extended to the scenario where the exponent of the Barrow entropy allows to vary with the cosmological expansion of the universe. In both the cases (whether the Barrow exponent is a constant or varies with the cosmological evolution), we determine effective equation of state (EoS) parameter from the generalized holographic point of view, which, by…

In this letter we obtain wormhole solutions from the Karmarkar condition in f(Q) gravity formalism, in which Q is the nonmetricity scalar. We show that the combination of such ingredients provides us the possibility of obtaining traversable wormholes satisfying the energy conditions. Our results contribute to f(Q) gravity ascension, that was recently ignited by the natural prediction of early and late-time stages of universe expansion acceleration in the formalism.

We show that spin polarization of a fermion in a relativistic fluid at local thermodynamic equilibrium can be generated by the symmetric derivative of the four-temperature vector, defined as thermal shear. As a consequence, besides vorticity, acceleration and temperature gradient, also the shear tensor contributes to the polarization of particles in a fluid. This contribution to the spin polarization vector, which is entirely non-dissipative, adds to the well known term proportional to thermal vorticity and may thus have important consequences for the solution of the local polarization puzzles observed in relativistic heavy ion collisions.

We investigate the causal limit of maximum mass for stars in the framework of f(R) gravity. We choose a causal equation of state, with variable speed of sound, and with the transition density and pressure corresponding to the SLy equation of state. The transition density is chosen to be equal to twice the saturation density ρt∼2ρ0, and also the analysis is performed for the transition density, chosen to be equal to the saturation density ρt∼ρ0. We examine numerically the combined effect of the stiff causal equation of state and of the sound speed on the maximum mass of static neutron stars, in the context of Jordan frame of f(R) gravity. This yields the most extreme upper bound for neutron star masses in the context of extended gravity. As we will evince for the case of R2 model, the upper causal mass limit lies within, but not deeply in, the mass-gap region, and is marginally the same with the general relativistic causal maximum mass, indicating that the ∼3M⊙ general relativistic limit is respected. In view of the modified gravity perspective for the secondary component of the…

We use Big Bang Nucleosynthesis (BBN) data in order to impose constraints on the exponent of Barrow entropy. The latter is an extended entropy relation arising from the incorporation of quantum-gravitational effects on the black-hole structure, parameterized effectively by the new parameter Δ. When considered in a cosmological framework and under the light of the gravity-thermodynamics conjecture, Barrow entropy leads to modified cosmological scenarios whose Friedmann equations contain extra terms. We perform a detailed analysis of the BBN era and we calculate the deviation of the freeze-out temperature comparing to the result of standard cosmology. We use the observationally determined bound on |δTfTf| in order to extract the upper bound on Δ. As we find, the Barrow exponent should be inside the bound Δ≲1.4×10−4 in order not to spoil the BBN epoch, which shows that the deformation from standard Bekenstein-Hawking expression should be small as expected.

Radiation reaction (RR) terms at the third post-Minkowskian (3PM) order have recently been found to be instrumental in restoring smooth continuity between the non-relativistic, relativistic, and ultra-relativistic (including the massless) regimes. Here we propose a new and intriguing connection between RR and soft (bremsstrahlung) theorems which short-circuits the more involved conventional loop computations. Although first noticed in the context of the maximally supersymmetric theory, unitarity and analyticity arguments support the general validity of this 3PM-order connection that we apply, in particular, to Einstein's gravity and to its Jordan-Brans-Dicke extension. In the former case we find full agreement with a recent result by Damour obtained through a very different reasoning.

We map out the QCD phase structure at finite temperature and chemical potential for 2-flavour and 2+1-flavour QCD. This is done within a generalised functional approach to QCD put forward in [1]. Specifically we compute the quark propagator and the finite-temperature and density fluctuations of the gluon propagator and the quark-gluon vertex on the basis of precision data for vacuum correlation functions. The novel ingredient is the direct self-consistent computation of the DSEs for the three dominant dressings of the quark-gluon vertex, in contrast to the common use of STI-inspired vertices. For small densities the results for the chiral order parameter agree with the respective lattice and functional renormalisation group results, for large densities the present results are in a quantitative agreement with the latter, including the location of the critical end point.

We propose a novel primordial black hole (PBH) formation mechanism based on a first-order phase transition (FOPT). If a fermion species gains a huge mass in the true vacuum, the corresponding particles get trapped in the false vacuum as they do not have sufficient energy to penetrate the bubble wall. After the FOPT, the fermions are compressed into the false vacuum remnants to form non-topological solitons called Fermi-balls, and then collapse to PBHs due to the Yukawa attractive force. We derive the PBH mass and abundance, showing that for a O ( GeV ) FOPT the PBHs could be ∼ 10 17 g and explain all of dark matter. If the FOPT happens at higher scale, PBHs are typically overproduced and extra dilution mechanism is necessary to satisfy current constraints.

The concept of the Wigner function is used to construct a semi-classical kinetic theory describing the evolution of the axial current phase-space density of spin-12 particles in the relaxation time approximation. The resulting approach can be used to study spin polarization effects in relativistic matter, in particular, in heavy-ion collisions. An expression for the axial current based on the classical treatment of spin is also introduced and we show that it is consistent with earlier calculations using Wigner functions. Finally, we derive non-equilibrium corrections to the spin tensor, which are used to define, for the first time, the structure of spin transport coefficients in relativistic matter.

At low energies hadronic vacuum polarization (HVP) is strongly dominated by two-pion intermediate states, which are responsible for about 70% of the HVP contribution to the anomalous magnetic moment of the muon, aμHVP. Lattice-QCD evaluations of the latter indicate that it might be larger than calculated dispersively on the basis of e+e−→ hadrons data, at a level which would contest the long-standing discrepancy with the aμ measurement. In this Letter we study to which extent this 2π contribution can be modified without, at the same time, producing a conflict elsewhere in low-energy hadron phenomenology. To this end we consider a dispersive representation of the e+e−→2π process and study the correlations which thereby emerge between aμHVP, the hadronic running of the fine-structure constant, the P-wave ππ phase shift, and the charge radius of the pion. Inelastic effects play an important role, despite being constrained by the Eidelman–Łukaszuk bound. We identify scenarios in which aμHVP can be altered substantially, driven by changes in the phase shift and/or the inelastic…

We discuss a puzzle in relativistic spin hydrodynamics; in the previous formulation the spin source from the antisymmetric part of the canonical energy-momentum tensor (EMT) is crucial. The Belinfante improved EMT is pseudo-gauge transformed from the canonical EMT and is usually a physically sensible choice especially when gauge fields are coupled as in magnetohydrodynamics, but the Belinfante EMT has no antisymmetric part. We find that pseudo-transformed entropy currents are physically inequivalent in nonequilibrium situations. We also identify a current induced by the spin vorticity read from the Belinfante symmetric EMT.

Recent pulsar timing data reported by the NANOGrav collaboration may indicate the existence of a stochastic gravitational wave background around f∼10−8 Hz. We explore a possibility to generate such low-frequency gravitational waves from a dark sector phase transition. Assuming that the dark sector is completely decoupled from the visible sector except via the gravitational interaction, we find that some amount of dark radiation should remain until present. The NANOGrav data implies that the amount of dark radiation is close to the current upper bound, which may help mitigate the so-called Hubble tension. If the existence of dark radiation is not confirmed in the future CMB-S4 experiment, it would imply the existence of new particles feebly interacting with the standard model sector at an energy scale of O(1 - 100) MeV.

We discuss the impact of the recent O(αs3) calculations of the semileptonic width of the b quark and of the relation between pole and kinetic heavy quark masses by Fael et al. on the inclusive determination of |Vcb|. The most notable effect is a reduction of the uncertainty. Our final result is |Vcb|=42.16(51)10−3.

The recent experimental measurements on pp collisions at s=5.02TeV have shown a very large production of heavy baryons corresponding to a Λc/D0 ratio of about 0.5. This ratio is about one order of magnitude larger than what measured in e+e−, ep collisions, and is larger of about a factor two respect to the forward rapidity ratio in pp collisions at LHC. We apply for the first time to pp collisions a quark coalescence plus fragmentation approach developed for AA collisions, assuming the formation of Hot QCD matter at finite temperature, which was able to correctly predict a Λc/D∼O(1) in AA collisions at RHIC energy. We calculate the heavy baryon/meson ratio and the pT spectra of charmed hadrons with and without strangeness content: D0, Ds, Λc+, Ξc and Ωc in pp collisions at top LHC energies, finding a satisfactory result for the measured Λc+/D0 and the Ξc/D0. At variance with other approaches a coalescence approach predicts also a significant production of Ωc such that Ωc/D0∼O(10−1).

Primordial black holes (PBHs) from the early Universe have been connected with the nature of dark matter and can significantly affect cosmological history. We show that coincidence dark radiation and density fluctuation gravitational wave signatures associated with evaporation of ≲109 g PBHs can be used to explore and obtain important hints about the formation mechanisms of spinning and non-spinning PBHs spanning orders of magnitude in mass-range, which is challenging to do otherwise.

We calculate the 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.

Recent progress in the determination of both masses and radii of neutron stars has put strong constraints on the equation of state (EoS) above the nuclear saturation density. Within a confining quark matter model, we propose an anisotropic star consisting of a homogeneous and unpaired charge-neutral 3-flavor interacting quark matter with O(ms4) corrections in the context of Einstein-Gauss-Bonnet gravity theory. This generalized model depends only on three free parameters: the bag constant B, the interaction parameter a and the Gauss-Bonnet coupling constant α. Given the underlying EoS, we show the possibility of obtaining the maximal neutron star mass which satisfies the recent observational data for PSR J0751+1807. The numerical analysis of mass-radius relations supports the existence of other massive pulsars with a maximum mass consistent and common radii in the range of R≲(11∼14) Km [1]. Furthermore, we discuss the mass vs central mass density (M−ρc) relation for stability, compactness and binding energy in this gravity theory. Our results thus provide circumstantial evidence in…

Recently the LHCb collaboration has confirmed the evidence for lepton flavour nonuniversality at the 3.1σ level via an updated measurement of RK. In this work we analyse this evidence within a model-independent approach. We make projections for future measurements which indicate that LHCb will be in the position to discover lepton nonuniversality with the Run 3 data in a single observable. We analyse other ratios based on our analysis of the present measurements of the ratios RK(⁎) and analyse if they are able to differentiate between various new physics options within the effective field theory at present or in the near future. We also compare the present deviations in the ratios with NP indications in the angular observables of exclusive b→sℓℓ transitions. Finally, we update our global analysis considering all b→sℓℓ observables altogether, including a 20-parameter fit in connection of a Wilks' test.

Recently, Cardoso et al. [1] found an exact solution describing the black hole immersed in a galactic-like distribution of matter. There, the properties of gravitational radiation were studied. Here we continue analysis of properties of this geometry via consideration of the electromagnetic radiation. We calculate quasinormal modes, asymptotic tails and grey-body factors for electromagnetic radiation. In addition, we discuss the Unruh temperature for this spacetime. Estimations made in the regime which is best fitting the galaxies behavior show that influence of the environment on classical and quantum radiation around such black holes must be relatively small.

We discuss the effect of rapid rotation on the phase diagram of hadronic matter. The energy dispersion relation is shifted by an effective chemical potential induced by rotation. This suggests that rotation should lower the critical temperature of chiral restoration, but it is still controversial how the deconfinement temperature should change as a function of angular velocity. We adopt the hadron resonance gas model as an approach free from fitting parameters. We identify the deconfinement from the thermodynamic behavior and find that rotation decreases the deconfinement temperature. We also discuss the spatial inhomogeneity of the pressure and give a semi-quantitative estimate of the moment of inertia.

We calculate exclusive production of a longitudinally polarized heavy vector meson at next-to-leading order in the dipole picture. The large quark mass allows us to separately include both the first QCD correction proportional to the coupling constant αs, and the first relativistic correction suppressed by the quark velocity v2. Both of these corrections are found to be numerically important in J/ψ production. The results obtained are directly suitable for phenomenological calculations. We also demonstrate how vector meson production provides complementary information to structure function analyses when one extracts the initial condition for the energy evolution of the proton small-x structure.

We investigate the spin alignment of vector mesons arising from locally polarized quarks and anti-quarks (local spin alignment) in heavy-ion collisions. We find that ρ00≠1/3 does not necessarily signal the global polarization of quarks and anti-quarks along the orbital angular momentum of the system, but may also originate from their local spin polarization. Such local spin polarization could be induced by local vorticity arising from the anisotropic expansion of the fireball. We further propose experimental observables that can distinguish between the local and the global spin alignments. Measurements of these observables in heavy-ion collisions can probe the vorticity pattern and shed light on the puzzles of ϕ and K⁎0 spin alignments.

Quantum gravity effects in effective models of loop quantum gravity, such as loop quantum cosmology, are encoded in the choice of so-called polymerisation schemes. Physical viability of the models, such as an onset of quantum effects at curvature scales near the Planck curvature, severely restricts the possible choices. An alternative point of view on the choice of polymerisation scheme is to choose adapted variables so that the scheme is the simplest possible one, known as μ0-scheme in loop quantum cosmology. There, physically viable models with μ0-scheme polymerise the Hubble rate b that is directly related to the Ricci scalar and the matter energy density on-shell. Consequently, the onset of quantum effects depends precisely on those parameters. In this letter, we construct similar variables for black to white hole transitions modelled using the description of the Schwarzschild interior as a Kantowski-Sachs cosmology. The resulting model uses the μ0-scheme and features sensible physics for a broad range of initial conditions (= choices of black and white hole masses) and favours…

The effects of neutron skin on the multiplicity (Nch) and eccentricity (ϵ2) in relativistic 4496Ru+4496Ru and 4096Zr+4096Zr collisions at sNN=200 GeV are investigated with the Trento model. It is found that the Ru+Ru/Zr+Zr ratios of the Nch distributions and ϵ2 in mid-central collisions are exquisitely sensitive to the neutron skin type (skin vs. halo). The state-of-the-art calculations by energy density functional theory (DFT) favor the halo-type neutron skin and can soon be confronted by experimental data. It is demonstrated that the halo-type density can serve as a good surrogate for the DFT density, and thus can be efficiently employed to probe nuclear deformities by using elliptic flow data in central collisions. We provide hereby a proof-of-principle venue to simultaneously determine the neutron skin type, thickness, and nuclear deformity.

Dark matter (DM) interacting only gravitationally with the standard model could have been produced in the early universe by Hawking evaporation of primordial black holes (PBH). This mechanism is viable in a large range of DM mass, spanning up to the Planck scale. However, DM is also unavoidably produced by the irreducible UV gravitational freeze-in. We show that the latter mechanism sets strong bounds, excluding large regions of the parameter space favored by PBH production.

The current observational constraints still leave a substantial mass window ∼[10−16,10−14]∪[10−13,10−12]M⊙ for primordial black holes (PBHs) representing all of dark matter (DM) in our Universe. The gravitational waves (GWs) induced by the curvature perturbations are inevitably generated during the formation of these PBHs, and fall in the frequency band of LISA. Such scalar induced gravitational waves (SIGWs) are supposed to be definitely detected by LISA even when the second-order local-type non-Gaussianity characterized by the parameter FNL is taken into account. In this letter, we give a comprehensive analysis of the GWs induced by the local-type non-Gaussian curvature perturbations up to the third-order denoted by the non-linear parameter GNL, and we find that a log-dependent slope of SIGWs in the infrared region is generically predicted and the amplitude of SIGWs can be further suppressed by several orders of magnitude. As a result, the null-detection of SIGWs by LISA cannot rule out the possibility of PBHs making up all of DM.

A coupled-channel analysis of BESIII data on radiative J/ψ decays into ππ, KK¯, ηη and ωϕ has been performed. The partial-wave amplitude is constrained by a large number of further data. The analysis finds ten isoscalar scalar mesons. Their masses, widths and decay modes are determined. The scalar mesons are interpreted as mainly SU(3)-singlet and mainly octet states. Octet isoscalar scalar states are observed with significant yields only in the 1500-2100 MeV mass region. Singlet scalar mesons are produced over a wide mass range but their yield peaks in the same mass region. The peak is interpreted as scalar glueball. Its mass and width are determined to M=1865±25−30+10 MeV and Γ=370±50−20+30 MeV, its yield in radiative J/ψ decays to (5.8±1.0)10−3.

We consider the contribution of scalar resonances to hadronic light-by-light scattering in the anomalous magnetic moment of the muon. While the f0(500) has already been addressed in previous work using dispersion relations, heavier scalar resonances have only been estimated in hadronic models so far. Here, we compare an implementation of the f0(980) resonance in terms of the coupled-channel S-waves for γ⁎γ⁎→ππ/K¯K to a narrow-width approximation, which indicates aμHLbL[f0(980)]=−0.2(2)×10−11. With a similar estimate for the a0(980), the combined effect is thus well below 1×10−11 in absolute value. We also estimate the contribution of heavier scalar resonances. In view of the very uncertain situation concerning their two-photon couplings we suggest to treat them together with other resonances of similar mass when imposing the matching to short-distance constraints. Our final result is a refined estimate of the S-wave rescattering effects in the ππ and K¯K channel up to about 1.3 GeV and including a narrow-width evaluation of the a0(980): aμHLbL[scalars]=−9(1)×10−11.

Bound states of double-heavy tetraquarks are studied in a constituent quark model. Two bound states are found for isospin and spin-parity I(JP)=0(1+) in the bbu¯d¯ channel. One is deeply bound and compact made of colored diquarks, while the other is shallow and extended as a BB⁎ molecule. The former agrees well with lattice QCD results. A systematic decrease in the binding energy is seen by replacing one of the heavy quarks to a lighter one. Altogether we find ten bound states. It is shown for the first time that hadrons with totally different natures emerge from a single Hamiltonian.

Primordial black holes (PBHs) can constitute the predominant fraction of dark matter (DM) if PBHs reside in the currently unconstrained “sublunar” mass range. PBHs originating from scalar perturbations generated during inflation can naturally appear with a broad spectrum in a class of models. The resulting stochastic gravitational wave (GW) background generated from such PBH production can account for the recently reported North American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array data signal, and will be testable in future GW observations by interferometer-type experiments such as Laser Interferometer Space Antenna (LISA). We show that the broad mass function of such PBH DM is already being probed by Subaru Hyper Suprime-Cam (HSC) microlensing data and is consistent with a detected candidate event. Upcoming observations of HSC will be able to provide an independent definitive test of the stochastic GW signals originating from such PBH DM production scenarios.

We study the scaling properties of the finite temperature QCD phase transition, for light quark masses ranging from the heavy quark regime to their physical values. The lattice results are obtained in the fixed scale approach from simulations of Nf=2+1+1 flavours of Wilson fermions at maximal twist. We identify an order parameter free from the linear contributions in mass due to additive renormalization and regular terms in the Equation of State, which proves useful for the assessment of the hypothesized universal behaviour. We find compatibility with the 3D O(4) universality class for the physical pion mass and temperatures 120 MeV ≲T≲300 MeV. We discuss violation of scaling at larger masses and a possible cross-over to mean field behaviour. The chiral extrapolation T0=134−4+6 MeV of the pseudocritical temperature is robust against predictions of different universality classes and consistent with its estimate from the O(4) Equation of State for the physical pion mass.

The Standard Model (SM) is augmented with a U(1)B−3Lμ gauge symmetry spontaneously broken above the TeV scale when an SM-singlet scalar condenses. Scalar leptoquarks S1(3)=(3‾,1(3),13) charged under U(1)B−3Lμ mediate the intriguing effects observed in muon (g−2), RK(⁎), and b→sμ+μ− angular distributions, while generically evading all other phenomenological constraints. The fermionic sector is minimally extended with three right-handed neutrinos, and a successful type-I seesaw mechanism is realized. Charged lepton flavor violation is effectively suppressed, and proton decay—a common prediction of leptoquarks—is postponed to the dimension-6 effective Lagrangian. Unavoidable radiative corrections in the Higgs mass and muon Yukawa favor leptoquark masses interesting for collider searches. The parameters of the model are radiatively stable and can be evolved by the renormalization group to the Planck scale without inconsistencies. Alternative lepton-flavored gauge extensions of the SM, under which leptoquarks become muoquarks, are proposed for comparison.

Recently, a new hadronic structure at around 6.9 GeV was observed in an LHCb experiment. From its limited yet known decay mode, one could still determine that it contains at least four charm quarks and hence belongs to the category of exotic state. This finding indicates for the first time the tetracharm exotic states and is therefore quite importance. In this letter, we propose a nature hybrid interpretation for the structure of X(6900), i.e. in [3¯c]cc⊗[8c]G⊗[3c]c¯c¯ configuration with JPC=0++, and by using the QCD Sum Rule technique we performed mass spectrum calculation. The results showed that the observed X(6900) could be a gluonic tetracharm state, and some other structures may exist, e.g., one around 7.2 GeV in the tetracharm hybrid configuration and with JPC=0−+. We also predict the tetrabottom hybrid states, leaving for future experiment.

The first measurement of the cross section for coherent J / ψ photoproduction as a function of | t | , the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair s NN = 5.02 TeV with the J / ψ produced in the central rapidity region | y | < 0.8 , which corresponds to the small Bjorken- x range ( 0.3 − 1.4 ) × 10 − 3 . The measured | t | -dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x .

We use MUSE spectroscopic observations of the dwarf spheroidal galaxy Leo T between 470 and 935 nm to search for radiative decays of axion like particles (ALPs). Under the assumption that ALPs constitute the dark matter component of the Leo T halo, we derive bounds on the effective ALP-two-photon coupling. We improve existing limits by more than one order of magnitude in the ALP mass range 2.7-5.3 eV.

We study observational constraints on the modified symmetric teleparallel gravity, the non-metricity f(Q) gravity, which reproduces background expansion of the universe. For this purpose, we use Hubble measurements, Baryonic Acoustic Oscillations (BAO), 1048 Pantheon supernovae type Ia data sample which integrate SuperNova Legacy Survey (SNLS), Sloan Digital Sky Survey (SDSS), Hubble Space Telescope (HST) survey, Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1). We confront our cosmological model against observational samples to set constraints on the parameters using Markov Chain Monte Carlo (MCMC) methods. We find the equation of state parameter ω=−0.853−0.020+0.015 and ω=−0.796−0.074+0.049 for Hubble and Pantheon samples, respectively. As a result, the f(Q) model shows the quintessence behavior and deviates from ΛCDM.

We consider the uncertainty in the arm length of an interferometer due to metric fluctuations from the quantum nature of gravity, proposing a concrete microscopic model of energy fluctuations in holographic degrees of freedom on the surface bounding a causally connected region of spacetime. In our model, fluctuations longitudinal to the beam direction accumulate in the infrared and feature strong long distance correlation in the transverse direction. This leads to a signal that could be observed in a gravitational wave interferometer. We connect the positional uncertainty principle arising from our calculations to the 't Hooft gravitational S-matrix.

The NA62 experiment at CERN reports searches for K + → μ + N and K + → μ + ν X decays, where N and X are massive invisible particles, using the 2016–2018 data set. The N particle is assumed to be a heavy neutral lepton , and the results are expressed as upper limits of O ( 10 − 8 ) of the neutrino mixing parameter | U μ 4 | 2 for N masses in the range 200–384 MeV/ c 2 and lifetime exceeding 50 ns. The X particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for X masses in the range 10–370 MeV/ c 2 are reported for the first time, ranging from O ( 10 − 5 ) to O ( 10 − 7 ) . An improved upper limit of 1.0 × 10 − 6 is established at 90% CL on the K + → μ + ν ν ν ¯ branching fraction.

The kernel ridge regression (KRR) approach is extended to include the odd-even effects in nuclear mass predictions by remodulating the kernel function without introducing new weight parameters and inputs in the training network. By taking the WS4 mass model as an example, the mass for each nucleus in the nuclear chart is predicted with the extended KRR network, which is trained with the mass model residuals, i.e., deviations between experimental and calculated masses, of other nuclei with known masses. The resultant root-mean-square mass deviation from the available experimental data for the 2353 nuclei with Z≥8 and N≥8 can be reduced to 128 keV, which provides the most precise mass model from machine learning approaches so far. Moreover, the extended KRR approach can avoid the risk of worsening the mass predictions for nuclei at large extrapolation distances, and meanwhile, it provides a smooth extrapolation behavior with respect to the odd and even extrapolation distances.

In this letter we propose a reduction of the H0 tension puzzle by means of a theory of minimally modified gravity which is dubbed VCDM. After confronting the theory with the data, a transition in the expansion history of the universe in the low-redshift z≃0.3 is found. From the bestfit values the total fitness parameter is improved by Δχ2=33.41, for the data set considered. We then infer the local Hubble expansion rate today within this theory by means of low redshift Pantheon data. The resulting local Hubble expansion rate today is H0loc=73.69±1.4. Hence the tension is reduced within the VCDM theory.

A recent update from MiniBooNE has strengthened the observed 4.8σ excess of e-like events. Motivated by this and other notable deviations from standard model predictions, such as the muon (g−2), we propose a solution to low energy anomalies through a dark neutrino sector. The model is renormalizable and can also explain light neutrino masses with an anomaly-free and dark U(1)′ gauge symmetry broken at the GeV scale. Large kinetic mixing leads to s-channel production of heavy neutral leptons at e+e− colliders, where we point out and explain a ≳2σ excess observed in the BaBar monophoton data. Our model is also compatible with anomalous e-like events seen at old accelerator experiments, as well as with an excess of double vertex signatures observed at CCFR.

A search for leptoquarks produced singly and in pairs in proton-proton collisions is presented. We consider the leptoquark (LQ) to be a scalar particle of charge −1/3 e coupling to a top quark plus a tau lepton ( t τ ) or a bottom quark plus a neutrino ( b ν ), or a vector particle of charge +2/3 e , coupling to t ν or b τ . These choices are motivated by models that can explain a series of anomalies observed in the measurement of B meson decays. In this analysis the signatures t τ ν b and t τ ν are probed, using data recorded by the CMS experiment at the CERN LHC at s = 13 TeV and that correspond to an integrated luminosity of 137 fb −1 . These signatures have not been previously explored in a dedicated search. The data are found to be in agreement with the standard model prediction. Lower limits at 95% confidence level are set on the LQ mass in the range 0.98–1.73 TeV, depending on the LQ spin and its coupling λ to a lepton and a quark, and assuming equal couplings for the two LQ decay modes considered. These are the most stringent constraints to date on the existence of…

α -particle preformation factors, one of the most significant quantities in α decay, are systematically investigated, which are extracted from the ratios between theoretical α -decay half-lives calculated by the generalized liquid drop model and experimental data. The results indicate that both α -particle preformation factors P α and α decay energy Q α are important observed quantities for revealing the nuclear shell structure information. And a nice linear relationship exists between log 10 ⁡ P α and Q α − 1 / 2 , which means the famous Geiger-Nuttall law can not only describe α decay half-lives but deal with α -particle preformation factors, as well as the nuclear shell effects play key roles in α -particle preformation. Furthermore, the results indicate that Z = 82 and N = 126 closed shells play more important roles than Z = 50 and N = 82 shell closures in which the shell effect of N = 126 is stronger than that of Z = 82 in the α decay process. Besides, the unpaired nucleons will inhibit the preformation of α -particle. After considering the above significant physical effects, a…

The generalized parton distributions (GPDs) offer a window on three-dimensional imaging of the nucleon, providing understanding of how the fundamental properties of the nucleon, such as its mass and spin, arise from the underlying quark and gluon degrees of freedom. In this work, we present the first lattice calculation of the nucleon isovector helicity GPD at physical pion mass, using an a≈0.09 fm lattice ensemble with 2+1+1 flavors of highly improved staggered quarks generated by MILC Collaboration. We perform the GPD calculation in Breit frame using averaged nucleon boost momentum Pz≈2.2 GeV with nonzero momentum transfers in [0.2,1.0] GeV2. Nonperturbative renormalization in RI/MOM scheme is used to obtain the quasi-distribution before matching to the lightcone GPDs. The three-dimensional distribution H˜(x,Q2) is presented, along with the three-dimensional nucleon tomography and impact-parameter–dependent distribution for selected Bjorken x at μ=3 GeV in MS‾ scheme.

We construct a novel charged Taub-NUT spacetime, providing a first non-trivial example of a self-gravitating solution to the recently proposed ModMax theory [1], [2], the most general (1-parametric) theory of non-linear electrodynamics that is characterized by both the conformal symmetry and the SO(2) duality-rotation invariance. The spacetime features non-trivial magnetic fields, in their presence the non-linearity of the field becomes apparent and the solution is distinguished from that of the Maxwell theory. The thermodynamics of the new solution, the charged black hole limit of vanishing NUT parameter, and the self-dual solutions are also briefly discussed.

A new generalized ModMax model of nonlinear electrodynamics with four parameters is proposed. The ModMax model and Born–Infeld-type electrodynamics are particular cases of the present model. It is shown that a singularity of the electric field at the center of point-like charged particles is absent. We found corrections to Coulomb's law at r→∞ and obtained the total electrostatic and magnetic energies of point-like charges. Free electric and magnetic charges and their densities are obtained.

We calculate the potential contributions of the Hamiltonian in harmonic coordinates up 6PN for binary mass systems to O(GN4) and perform comparisons to recent results in the literature [1] and [2].

We calculate the collinear anomalous dimensions in massless four-loop QCD and N=4 supersymmetric Yang-Mills theory from the infrared poles of vertex form factors. We give very precise numerical approximations and a conjecture for the complete analytic results in both models we consider.

We discuss the emergence of black hole shadow and photon-sphere in the context of f(R) gravity. It is shown that the shadow is exponentially sensitive to linear instabilities of metric coming from some f(R) solutions. Thus, the instabilities of photon circular trajectories, delimiting the black hole photon-sphere, are double exponentialized. Specifically we individuate two Lyapunov exponents, rather than only one, related to two different sources of chaos in geodesic orbits as a sort of butterfly effect. Such a result violates the black hole chaos bound proposed by Maldacena, Shenker and Stanford for General Relativity. We also explore the impact of the black hole metric instabilities in f(R) gravity on the quasi-normal modes. In the framework of Extended Theories of Gravity, our analysis suggests a new paradigm to deal with black hole shadow and gravitational waves observations coming from black hole merging in the ringdown phase.