Mon·Apr 24, 2017Monday·April 24, 2017

1. 01*

   Low-shear QCD plasma from perturbation theory

   Greg Jackson🇿🇦 · Andre Peshier🇿🇦

   We argue that the phenomenologically inferred ratio of shear viscosity to entropy density of the quark-gluon plasma, $\eta /\text{s}<0.5$ near the deconfinement temperature $T_c$, can be understood from perturbative QCD. To rebut the widespread, opposite view we first show that, and why, the existing leading order result in (fixed) coupling should not be further expanded in logarithms. Emphasizing then that the resummation mandatory for screening also settles the often neglected question of scale setting for the running coupling, we establish a temperature dependence of $\eta /\text{s}$ which agrees well with constraints from hydrodynamics.

   hep-phMDPI Proc.(2019)·2 citations
2. 02*

   Minima of multi-Higgs potentials with triplets of $\Delta (3n^2)$ and $\Delta (6n^2)$

   Ivo de Medeiros Varzielas🇬🇧 · Stephen F. King🇬🇧 · Christoph Luhn🇩🇪 · Thomas Neder🇪🇸

   We analyse the minima of scalar potentials for multi-Higgs models where the scalars are arranged as either one triplet or two triplets of the discrete symmetries $A_4$, $S_4$, $\Delta (27)$, $\Delta (54)$, as well as $\Delta (3n^2)$ and $\Delta (6n^2)$ with $n>3$. The results should be useful for both multi-Higgs models involving electroweak doublets and multi-flavon models involving electroweak singlets, where in both cases the fields transform as triplets under some non-Abelian discrete symmetry.

   hep-phPLB(2017)·22 citations
3. 03*

   What does a non-vanishing neutrino mass have to say about the strong CP problem?

   P. Q. Hung🇺🇸

   A new solution to the strong CP problem with distinct experimental signatures at the LHC is proposed. It is based on the Yukawa interactions between mirror quarks, Standard Model (SM) quarks and Higgs singlets. (Mirror quarks and leptons which include non-sterile right-handed neutrinos whose Majorana masses are proportional to the electroweak scale, form the basis of the EW-${\nu }_R$ model.) The aforementioned Yukawa couplings can in general be complex and can contribute to $ArgDetM$ ($\bar{\theta }={\theta }_{QCD}+ArgDetM$) at tree-level. The crux of matter in this manuscript is the fact that {\em no matter how large} the CP-violating phases in the Yukawa couplings might be, $ArgDetM$ can remain small i.e. $\bar{\theta }<10^{-10}$ for reasonable values of the Yukawa couplings and, in fact, vanishes when the VEV of the Higgs singlet (responsible for the Dirac part of the neutrino mass in the seesaw mechanism) vanishes. The smallness of the contribution to $\bar{\theta }$ is {\em principally due} to the smallness of the ratio of the two mass scales in the seesaw mechanism: the Dirac and Majorana mass scales.

   hep-ph7 citations
4. 04*

   Electroweak production of Higgs boson pairs in 2HDMs

   Rikard Enberg🇸🇪 · William Klemm🇬🇧 · Stefano Moretti🇬🇧 · Shoaib Munir🇰🇷

   One of the main features of a Two-Higgs Doublet Model (2HDM) is the presence of two additional neutral Higgs states, besides the one mimicking the ~125 GeV state observed at the LHC. The three Higgs bosons of a 2HDM can be produced at the LHC either singly via gluon fusion or in pairs with each other. When analyzing their pair production, the emphasis is laid on gluon-initiated processes, and the electroweak (EW) production is generally not treated on the same footing, assuming its contribution to be highly subleading. We show here that when the sum of the masses of the lightest scalar and pseudoscalar Higgs bosons in the Type-I 2HDM is smaller than the Z-boson mass, their EW pair production can dominate over QCD pair production by orders of magnitude.

   hep-phPoS(2017)·2 citations
5. 05*

   Crossover-model approach to QCD phase diagram, equation of state and susceptibilities in the 2+1 and 2+1+1 flavor systems

   Akihisa Miyahara🇯🇵 · Masahiro Ishii🇯🇵 · Hiroaki Kouno🇯🇵 · Masanobu Yahiro🇯🇵

   We construct a simple model for describing the hadron-quark crossover transition by using lattice QCD (LQCD) data in the 2+1 flavor system, and draw the phase diagram in the 2+1 and 2+1+1 flavor systems through analyses of the equation of state (EoS) and the susceptibilities. In the present hadron-quark crossover (HQC) model is successful in reproducing LQCD data on the EoS and the flavor susceptibilities.We define the hadron-quark transition temperature. For the 2+1 flavor system, the transition line thus obtained is almost identical in planes that are created by temperature and the chemical potential for the baryon-number(B), the isospin(I), the hypercharge(Y), when the chemical potentials are smaller than 250 MeV. This BIY approximate equivalence persists also in the 2+1+1 flavor system. We plot the phase diagram also in planes that are created by temperature and the chemical potential for u,d,s quark number in order to investigate flavor dependence of transition lines. In the 2+1+1 flavor system, c quark does not affect the 2+1 flavor subsystem composed of u, d, s. The flavor off-diagonal susceptibilities are good indicators to see how hadrons survive as T increases, since the independent quark model hardly contributes to them.

   hep-phhep-latnucl-thInt.J.Mod.Phys.A(2017)·6 citations
6. 06*

   Towards the fate of the oscillating false vacuum

   Luc Darmé🇵🇱 · Joerg Jaeckel🇩🇪 · Marek Lewicki🇵🇱

   Motivated by cosmological examples we study quantum field theoretical tunnelling from an initial state where the "classical field", i.e. the vacuum expectation value of the field operator is spatially homogeneous but performing a time-dependent oscillation about a local minimum. In particular we estimate both analytically and numerically the exponential contribution to the tunnelling probability. We additionally show that after the tunnelling event, the classical field solution - the so-called "bubble" - mediating the phase transition can either grow or collapse. We present a simple analytical criterium to distinguish between the two behaviours.

   hep-phhep-thPRD(2017)·23 citations
7. 07*

   Two Body Hadronic Decays ${\Lambda }_b({\frac{1}{2}}^{+})\to B^{\ast }({\frac{3}{2}}^{+})+P$ in a quark model

   Fayyazuddin🇵🇰

   The framework under which decays ${\Lambda }_b({\frac{1}{2}}^{+})\to B({\frac{1}{2}}^{+})+M$ are analyzed is not applicable for the decays ${\Lambda }_b({\frac{1}{2}}^{+})\to B^{\ast }({\frac{3}{2}}^{+})+M$. These decays occur through a baryon pole ${\Sigma }_c^0$ which is generated by the W-exchange diagram in the process $b+u\stackrel{W}{\to }c+d$. The effective Hamiltonian which arises from the W-exchange diagram is expressed in the non relativistic limit. Since belongs to representation $6$ of SU(3), it contributes to two sets of decays: ${\Lambda }_b\to {\Delta }^0{D}^0,{\Delta }^{-}{D}^{+},$ and ${\Lambda }_b\to {\Sigma }_c^{\ast -}{\pi }^{+},$. The branching ratios for these decays are evaluated which can be compared with their experimental values when the data become available. Other prediction of the model is that asymmetry parameter $\alpha =0$, since baryon pole contributes to parity conserving (p-wave) amplitude and does not contribute to parity violating (d-wave) amplitude.

   hep-phPRD(2017)·5 citations
8. 08*

   Magnetic field influence on the early time dynamics of heavy-ion collisions

   Moritz Greif🇩🇪 · Carsten Greiner🇩🇪 · Zhe Xu🇨🇳

   In high energy heavy-ion collisions the magnetic field is very strong right after the nuclei penetrate each other and a non-equilibrium system of quarks and gluons builds up. Even though quarks might not be very abundant initially, their dynamics must necessarily be influenced by the Lorentz force. Employing the 3+1d partonic cascade BAMPS we show that the circular Larmor movement of the quarks leads to a strong positive anisotropic flow of quarks at very soft transverse momenta. We explore the regions where the effect is visible, and explicitly show how collisions damp the effect. As a possible application we look at photon production from the flowing non-equilibrium medium.

   hep-phnucl-thPRC(2017)·25 citations
9. 09*

   Dark matter reflection of particle symmetry

   M.Yu. Khlopov🇷🇺

   In the context of the relationship between physics of cosmological dark matter and symmetry of elementary particles a wide list of dark matter candidates is possible. New symmetries provide stability of different new particles and their combination can lead to a multicomponent dark matter. The pattern of symmetry breaking involves phase transitions in very early Universe, extending the list of candidates by topological defects and even primordial nonlinear structures.

   hep-phMod.Phys.Lett.A(2017)·6 citations
10. 10*

    Particle Dark Matter Candidates

    M.Yu. Khlopov🇷🇺

    A series of brief reviews collected in the present issue present various candidates for cosmological Dark Matter (DM) predicted by models of particle physics. The range from superlight axions to extended objects is covered. Though the possible list of candidates is far from complete it gives the flavor of the extensive field of Dark matter particle physics.

    hep-phMod.Phys.Lett.A(2017)·8 citations
11. 11*

    Simplified Models for Displaced Dark Matter Signatures

    Oliver Buchmueller🇬🇧 · Albert De Roeck🇨🇭 · Matthew McCullough🇨🇭 · Kristian Hahn🇺🇸 · Kevin Sung🇺🇸 · Pedro Schwaller🇩🇪 · Tien-Tien Yu🇨🇭

    We propose a systematic programme to search for long-lived neutral particle signatures through a minimal set of displaced searches requiring significant missing transverse energy (dMETs). Our approach is to extend the well-established dark matter simplified models to include displaced vertices. The dark matter simplified models are used to describe the primary production vertex. A displaced secondary vertex, characterised by the mass of the long-lived particle and its lifetime, is added for the displaced signature. We show how these models can be motivated by, and mapped onto, complete models such as gauge-mediated SUSY breaking and models of neutral naturalness. We also outline how this approach may be used to extend other simplified models to incorporate displaced signatures and to characterise searches for long-lived charged particles. Displaced vertices are a striking signature with virtually no backgrounds from SM processes, and thus provide an excellent target for the high-luminosity run of the Large Hadron Collider. The proposed models and searches provide a first step towards a systematic broadening of the displaced dark matter search programme.

    hep-phhep-exJHEP(2017)·39 citations
12. 12*

    Drell-Yan-like processes and duality

    I.V. Anikin🇷🇺 · L. Szymanowski🇵🇱 · O.V. Teryaev🇷🇺 · N. Volchanskiy🇷🇺

    We calculate the gauge invariant Drell-Yan-like hadron tensors. In connection with new COMPASS results, we propose the single spin asymmetry which probes gluon poles together with chiral-odd and time-odd functions. The relevant pion production as a particular case of Drell-Yan-like process has been discussed. For the meson-induced Drell-Yan process, we model an analog of the twist three distribution function, which is a collinear function in inclusive channel, by means of two non-collinear distribution amplitudes which are associated with exclusive channel. This modelling demonstrates the fundamental duality between different factorization regimes.

    hep-phPRD(2017)·5 citations
13. 13*

    Accessing the topological susceptibility via the Gribov horizon

    D. Dudal🇧🇪 · C. P. Felix🇧🇪 · M. S. Guimaraes🇧🇷 · S. P. Sorella🇧🇷

    The topological susceptibility, ${\chi }^4$, following the work of Witten and Veneziano, plays a key role in identifying the relative magnitude of the ${\eta }^{\prime }$ mass, the so-called $U(1{)}_A$ problem. A nonzero ${\chi }^4$ is caused by the Veneziano ghost, the occurrence of an unphysical massless pole in the correlation function of the topological current. In a recent paper (Phys.Rev.Lett.114 (2015) 24, 242001), an explicit relationship between this Veneziano ghost and color confinement was proposed, by connecting the dynamics of the Veneziano ghost, and thus the topological susceptibility, with Gribov copies. However, the analysis is incompatible with BRST symmetry (Phys.Rev.D 93 (2016) no.8, 085010). In this paper, we investigate the topological susceptibility, ${\chi }^4$, in SU(3) and SU(2) Euclidean Yang-Mills theory using an appropriate Padé approximation tool and a non-perturbative gluon propagator, within a BRST invariant framework and by taking into account Gribov copies in a general linear covariant gauge.

    hep-phhep-thPRD(2017)·19 citations
14. 14*

    Mass Dependence of Higgs Production at Large Transverse Momentum

    Eric Braaten🇺🇸 · Hong Zhang🇺🇸 · Jia-Wei Zhang🇺🇸

    The transverse momentum distribution of the Higgs at large $P_T$ is complicated by its dependence on three important energy scales: $P_T$, the top quark mass $m_t$, and the Higgs mass $m_H$. A strategy for simplifying the calculation of the cross section at large $P_T$ is to calculate only the leading terms in its expansion in $m_t^2/P_T^2$ and/or $m_H^2/P_T^2$. The expansion of the cross section in inverse powers of $P_T$ is complicated by logarithms of $P_T$ and by mass singularities. In this paper, we consider the top-quark loop contribution to the subprocess $q\bar{q}\to H+g$ at leading order in ${\alpha }_s$. We show that the leading power of $1/P_T^2$ can be expressed in the form of a factorization formula that separates the large scale $P_T$ from the scale of the masses. All the dependence on $m_t$ and $m_H$ can be factorized into a distribution amplitude for $t\bar{t}$ in the Higgs, a distribution amplitude for $t\bar{t}$ in a real gluon, and an endpoint contribution. The factorization formula can be used to simplify calculations of the $P_T$ distribution at large $P_T$ to next-to-leading order in ${\alpha }_s$.

    hep-phJHEP(2017)·7 citations
15. 15*

    B physics Beyond the Standard Model at One Loop: Complete Renormalization Group Evolution below the Electroweak Scale

    Jason Aebischer🇨🇭 · Matteo Fael🇨🇭 · Christoph Greub🇨🇭 · Javier Virto🇨🇭

    General analyses of $B$-physics processes beyond the Standard Model require accounting for operator mixing in the renormalization-group evolution from the matching scale down to the typical scale of $B$ physics. For this purpose the anomalous dimensions of the full set of local dimension-six operators beyond the Standard Model are needed. We present here for the first time a complete and non-redundant set of dimension-six operators relevant for $B$-meson mixing and decay, together with the complete one-loop anomalous dimensions in QCD and QED. These results are an important step towards the automation of general New Physics analyses.

    hep-phJHEP(2017)·184 citations
16. 16*

    Forcer, a FORM program for the parametric reduction of four-loop massless propagator diagrams

    B. Ruijl (NIKHEF, Amsterdam & Leiden U.)🇳🇱 · T. Ueda🇳🇱 · J.A.M. Vermaseren (NIKHEF, Amsterdam)🇳🇱

    We explain the construction of Forcer, a FORM program for the reduction of four-loop massless propagator-type integrals to master integrals. The resulting program performs parametric IBP reductions similar to the three-loop Mincer program. We show how one can solve many systems of IBP identities parametrically in a computer-assisted manner. Next, we discuss the structure of the Forcer program, which involves recognizing reduction actions for each topology, applying symmetries, and transitioning between topologies after edges have been removed. This part is entirely precomputed and automatically generated. We give examples of recent applications of Forcer, and study the performance of the program. Finally we demonstrate how to use the Forcer package and sketch how to prepare physical diagrams for evaluation by Forcer.

    hep-phComput.Phys.Commun.(2020)·156 citations
17. 17*

    $R_{D^{(\ast )}}$ anomaly: A possible hint for natural supersymmetry with $R$-parity violation

    Wolfgang Altmannshofer🇺🇸 · P. S. Bhupal Dev🇺🇸 · Amarjit Soni🇺🇸

    Recently, several $B$-physics experiments have reported an appreciable deviation from the Standard Model (SM) in the tree-level observables $R_{D^{(\ast )}}$; the combined weighted average now stands at $\approx 4\sigma$. We first show the anomaly necessarily implies model-independent collider signals of the form $pp\to b\tau \nu$ that should be expediously searched for at ATLAS/CMS as a complementary test of the anomaly. Next we suggest a possible interconnection of the anomaly with the radiative stability of the Standard Model Higgs boson and point to a minimal effective supersymmetric scenario with $R$-parity violation as the underlying cause. We also comment on the possibility of simultaneously explaining the recently reported $R_{K^{(\ast )}}$ anomaly in this setup.

    hep-phhep-exPRD(2017)·198 citations
18. 18*

    A scale at 10 MeV, gravitational topological vacuum, and large extra dimensions

    Ufuk Aydemir🇸🇪

    We discuss a possible scale of gravitational origin at around $10$ MeV, or $10^{-12}$ cm, which arises in the MacDowell-Mansouri formalism of gravity due to the topological Gauss-Bonnet term in the action, as pointed out by Bjorken several years ago. A length scale of the same size emerges also in the Kodama solution in gravity, which is known to be closely related to the MacDowell-Mansouri formulation. We particularly draw attention to the intriguing incident that existence of six compact extra dimensions originated from TeV-scale quantum gravity as well points to a length scale of $10^{-12}$ cm, as the compactification scale. The presence of six such extra dimensions is also in remarkable consistency with the MacDowell-Mansouri formalism; it provides a possible explanation for the factor of $\sim 10^{120}$ multiplying the Gauss-Bonnet term in the action. We also comment on the relevant implications of such a scale regarding the thermal history of the universe motivated by the fact that it is considerably close to $1-2$ MeV below which the weak interactions freeze out, leading to Big Bang Nucleosynthesis.

    hep-phgr-qchep-thUniverse(2018)·7 citations
19. 19*

    Standardized Cumulants of Flow Harmonic Fluctuations

    Navid Abbasi🇮🇷 · Davood Allahbakhshi🇮🇷 · Ali Davody🇮🇷 · Seyed Farid Taghavi🇮🇷

    The distribution of flow harmonics in heavy ion experiment can be characterized by standardized cumulants. We first model the ellipticity and power parameters of the elliptic-power distribution by employing MC-Glauber model. Then we use the elliptic-power distribution together with the hydrodynamic linear response approximation to study the two dimensional standardized cumulants of elliptic and triangular flow ($v_2$ and $v_3$) distribution. For the second harmonic, it turns out that finding two dimensional cumulants in terms of $2q$-particle correlation functions $c_2\{2q\}$ is limited to the skewness. We also show that $c_3\{2\}$, $c_3\{4\}$, and $c_3\{6\}$, are related to the second, fourth, and sixth standardized cumulants of the $v_3$ distribution, respectively. The cumulant $c_n\{2q\}$ can be also written in terms of $v_n\{2q\}$. Specifically, $-(v_3\{4\}/v_3\{2\}{)}^4$ turns out to be the kurtosis of the $v_3$ event-by-event fluctuation distribution. We introduce a new parametrization for the distribution $p(v_3)$ with $v_3\{2\}$, kurtosis and sixth-order standardized cumulant being its free parameters. Compared to the Gaussian distribution, it indicates a more accurate fit with experimental results. Finally, we compare the kurtosis obtained from simulation with that of extracted from experimental data for the $v_3$ distribution.

    ↳ nucl-thhep-phPRC(2018)·21 citations
20. 20*

    Constraining spatial variations of the fine-structure constant in symmetron models

    A. M. M. Pinho🇵🇹 · M. Martinelli🇳🇱 · C. J. A. P. Martins🇵🇹

    We introduce a methodology to test models with spatial variations of the fine-structure constant $\alpha$, based on the calculation of the angular power spectrum of these measurements. This methodology enables comparisons of observations and theoretical models through their predictions on the statistics of the $\alpha$ variation. Here we apply it to the case of symmetron models. We find no indications of deviations from the standard behavior, with current data providing an upper limit to the strength of the symmetron coupling to gravity ($\log {\beta }^2<-0.9$) when this is the only free parameter, and not able to constrain the model when also the symmetry breaking scale factor $a_{SSB}$ is free to vary.

    ↳ astro-ph.COgr-qchep-phhep-thPLB(2017)·6 citations
21. 21*

    Charm Physics and CKM

    Carla Göbel🇧🇷

    An overview of the most important progresses in charm physics since the last CKM Workshop (2014) is presented. Due emphasis is given to the experimental measurements directly related to the CKM matrix.

    ↳ hep-exhep-phPoS(2017)·1 citation
22. 22*

    Finite-size behaviour of generalized susceptibilities in the whole phase plane of the Potts model

    Xue Pan🇨🇳 · Yanhua Zhang🇨🇳 · Lizhu Chen🇨🇳 · Mingmei Xu🇨🇳 · Yuanfang Wu🇨🇳

    We study the sign distribution of generalized magnetic susceptibilities in the temperature-external magnetic field plane using the three-dimensional three-state Potts model. We find that the sign of odd-order susceptibility is opposite in the symmetric (disorder) and broken (order) phases, but that of the even-order one remains positive when it is far away from the phase boundary. When the critical point is approached from the crossover side, negative fourth-order magnetic susceptibility is observable. It is also demonstrated that non-monotonic behavior occurs in the temperature dependence of the generalized susceptibilities of the energy. The finite-size scaling behavior of the specific heat in this model is mainly controlled by the critical exponent of the magnetic susceptibility in the three-dimensional Ising universality class.

    ↳ cond-mat.stat-mechhep-lathep-phhep-thCPC(2018)·1 citation
23. 23*

    Leading isospin-breaking corrections to pion, kaon and charmed-meson masses with Twisted-Mass fermions

    D. Giusti🇮🇹 · V. Lubicz🇮🇹 · G. Martinelli🇮🇹 · F. Sanfilippo🇮🇹 · S. Simula🇮🇹 · N. Tantalo🇮🇹 · C. Tarantino🇮🇹

    We present a lattice computation of the isospin-breaking corrections to pseudoscalar meson masses using the gauge configurations produced by the European Twisted Mass collaboration with $N_f=2+1+1$ dynamical quarks at three values of the lattice spacing ($a\simeq 0.062,0.082$ and $0.089$ fm) with pion masses in the range $M_{\pi }\simeq 210-450$ MeV. The strange and charm quark masses are tuned at their physical values. We adopt the RM123 method based on the combined expansion of the path integral in powers of the $d$- and $u$-quark mass difference (${\hat{m}}_d-{\hat{m}}_u$) and of the electromagnetic coupling ${\alpha }_{em}$. Within the quenched QED approximation, which neglects the effects of the sea-quark charges, and after the extrapolations to the physical pion mass and to the continuum and infinite volume limits, we provide results for the pion, kaon and (for the first time) charmed-meson mass splittings, for the prescription-dependent parameters ${ϵ}_{{\pi }^0}$, ${ϵ}_{\gamma }(\overline{MS},2\text{mbox}GeV)$, ${ϵ}_{K^0}(\overline{MS},2\text{mbox}GeV)$, related to the violations of the Dashen's theorem, and for the light quark mass difference $({\hat{m}}_d-{\hat{m}}_u)(\overline{MS},2\text{mbox}GeV)$.

    ↳ hep-lathep-phPRD(2017)·107 citations
24. 24*

    Hydrodynamic modeling of heavy-ion collisions

    Li Yan🇨🇦

    This contribution presents a theoretical overview of hydrodynamic modelling of heavy-ion collisions, with highlights on some recent developments. In particular, the formulation of anisotropic hydrodynamics, the role of hydrodynamic fluctuations, and the non-linear coupling of flow coefficients will be discussed.

    ↳ nucl-thhep-phnucl-exNPA(2017)·4 citations
25. 25*

    Phase space mass bound for fermionic dark matter from dwarf spheroidal galaxies

    Chiara Di Paolo🇮🇹 · Fabrizio Nesti🇮🇹 · Francesco L. Villante🇮🇹

    We reconsider the lower bound on the mass of a fermionic dark matter (DM) candidate resulting from the existence of known small Dwarf Spheroidal galaxies, in the hypothesis that their DM halo is constituted by degenerate fermions, with phase-space density limited by the Pauli exclusion principle. By relaxing the common assumption that the DM halo scale radius is tied to that of the luminous stellar component and by marginalizing on the unknown stellar velocity dispersion anisotropy, we prove that observations lead to rather weak constraints on the DM mass, that could be as low as tens of eV. In this scenario, however, the DM halos would be quite large and massive, so that a bound stems from the requirement that the time of orbital decay due to dynamical friction in the hosting Milky Way DM halo is longer than their lifetime. The smallest and nearest satellites Segue I and Willman I lead to a final lower bound of $m\gtrsim 100$ eV, still weaker than previous estimates but robust and independent on the model of DM formation and decoupling. We thus show that phase space constraints do not rule out the possibility of sub-keV fermionic DM.

    ↳ astro-ph.GAhep-phhep-thMNRAS(2018)·75 citations
26. 26*

    A tale of two modes: Neutrino free-streaming in the early universe

    Lachlan Lancaster🇺🇸 · Francis-Yan Cyr-Racine🇺🇸 · Lloyd Knox🇺🇸 · Zhen Pan🇺🇸

    We present updated constraints on the free-streaming nature of cosmological neutrinos from cosmic microwave background (CMB) power spectra, baryonic acoustic oscillation data, and local measurements of the Hubble constant. Specifically, we consider a Fermi-like four-fermion interaction between massless neutrinos, characterized by an effective coupling constant $G_{\mathrm{eff}}$, and resulting in a neutrino opacity ${\dot{\tau }}_{\nu }\propto G_{\mathrm{eff}}^2{T}_{\nu }^5$. Using a conservative prior on the parameter ${\log }_{10}\left(G_{\mathrm{eff}}{\mathrm{MeV}}^2\right)$, we find a bimodal posterior distribution. The first of these modes is consistent with the standard $\Lambda$CDM cosmology and corresponds to neutrinos decoupling at redshift $z_{\nu ,\mathrm{dec}}>1.3\times 10^5$. The other mode of the posterior, dubbed the "interacting neutrino mode", corresponds to neutrino decoupling occurring within a narrow redshift window centered around $z_{\nu ,\mathrm{dec}}\sim 8300$. This mode is characterized by a high value of the effective neutrino coupling constant, together with a lower value of the scalar spectral index and amplitude of fluctuations, and a higher value of the Hubble parameter. Using both a maximum likelihood analysis and the ratio of the two mode's Bayesian evidence, we find the interacting neutrino mode to be statistically disfavored compared to the standard $\Lambda$CDM cosmology. Interestingly, the addition of CMB polarization and direct Hubble constant measurements significantly raises the statistical significance of this secondary mode, indicating that new physics in the neutrino sector could help explain the difference between local measurements of $H_0$, and those inferred from CMB data. A robust consequence of our results is that neutrinos must be free streaming long before the epoch of matter-radiation equality.

    ↳ astro-ph.COhep-phJCAP(2017)·168 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.