Thu·Mar 22, 2018Thursday·March 22, 2018

1. 01*

   The QCD running coupling at all scales and the connection between hadron masses and \Lambda_s

   Alexandre Deur🇺🇸

   We report on recent experimental and theoretical developments in our understanding of the QCD running coupling \alpha_s in QCD's nonperturbative regime. They allow us to analytically compute the hadron mass spectrum, with \Lambda_s the only input necessary to this determination. The computed spectra agrees well with experimental data.

   hep-phFew Body Syst.(2018)·2 citations
2. 02*

   Resummation for (boosted) top-quark pair production at NNLO+NNLL' in QCD

   Michal Czakon🇩🇪 · Andrea Ferroglia🇺🇸 · David Heymes🇬🇧 · Alexander Mitov🇬🇧 · Ben D. Pecjak🇬🇧 · Darren J. Scott🇳🇱 · Xing Wang🇨🇳 · Li Lin Yang🇨🇳

   We construct predictions for top quark pair differential distributions at hadron colliders that combine state-of-the-art NNLO QCD calculations with double resummation at NNLL' accuracy of threshold logarithms arising from soft gluon emissions and of small mass logarithms. This is the first time a resummed calculation at full NNLO+NNLL' accuracy in QCD for a process with non-trivial color structure has been completed at the differential level. Of main interest to us is the stability of the M_{tt} and top-quark p_T distributions in the boosted regime where fixed order calculations may become strongly dependent on the choice of dynamic scales. With the help of numeric and analytic arguments we confirm that the choice for the factorization and renormalization scales advocated recently by some of the authors is indeed optimal. We further derive a set of optimized kinematics-dependent scales for the matching functions which appear in the resummed calculations. Our NNLO+NNLL' prediction for the top-pair invariant mass is significantly less sensitive to the choice of factorization scale than the fixed order prediction, even at NNLO. Notably, the resummed and fixed order calculations are in nearly perfect agreement with each other in the full M_{tt} range when the optimal dynamic scale is used. For the top-quark p_T distribution the resummation performed here has less of an impact and instead we find that upgrading the matching with fixed-order from NLO+NNLL' to NNLO+NNLL' to be an important effect, a point to be kept in mind when using NLO-based Monte Carlo event generators to calculate this distribution.

   hep-phhep-exJHEP(2018)·65 citations
3. 03*

   Photoproduction of light vector mesons in Xe-Xe ultraperipheral collisions at the LHC and the nuclear density of Xe-129

   V. Guzey (St. Petersburg, INP and Jyvaskyla U. and Helsinki Inst. of Phys.)🇷🇺 · E. Kryshen🇷🇺 · M. Zhalov (St. Petersburg, INP)🇷🇺

   We make predictions for cross sections of $\rho$ and $\varphi$ vector meson photoproduction in ultraperipheral Xe-Xe collisions at $\sqrt{s_{NN}}=5.44$ TeV. Analyzing the momentum transfer distribution of $\rho$ mesons in this process, we explore the feasibility of extracting the nuclear density of ${}^{129}$Xe, which is needed in searches for dark matter with Xenon-based detectors.

   hep-phnucl-thPLB(2018)·9 citations
4. 04*

   Big-bang nucleosynthesis and Leptogenesis in CMSSM

   Munehiro Kubo🇯🇵 · Joe Sato🇯🇵 · Takashi Shimomura🇯🇵 · Yasutaka Takanishi🇯🇵 · Masato Yamanaka🇯🇵

   We have investigated the constrained minimal supersymmetric standard model with three right-handed Majorana neutrinos whether there still is a parameter region which is consistent with all existing experimental data/limits such as Leptogenesis and the dark matter abundance and we also can solve the Lithium problem. Using Casas-Ibarra parameterization, we have found that a very narrow parameter space of the complex orthogonal matrix elements where the lightest slepton can have a long lifetime, that is necessary for solving the Lithium problem. Further, under this condition, there is a parameter region that can give an explanation for the experimental observations. We have studied three cases of the right-handed neutrino mass ratio \mbox{\em (i)} $M_2=2\times M_1$, \mbox{\em (ii)} $M_2=4\times M_1$, \mbox{\em (iii)} $M_2=10\times M_1$ while $M_3=40\times M_1$ is fixed. We have obtained the mass range of the lightest right-handed neutrino mass that lies between $10^9$ GeV and $10^{11}$ GeV. The important result is that its upper limit is derived by solving the Lithium problem and the lower limit comes from Leptogenesis. Calculated low-energy observables of these parameter sets such as BR($\mu \to e\gamma$) is not yet restricted by experiments and will be verified in the near future.

   hep-phPRD(2018)·5 citations
5. 05*

   Phenomenological study on the decay widths of ${\rm Y}(nS)\to {\bar{d}}^{\ast }(2380)+X$

   Chao-Yi Lü🇨🇳 · P. Wang🇨🇳 · Y. B. Dong🇨🇳 · P. N. Shen🇨🇳 · Z. Y. Zhang🇨🇳 · D. M. Li🇨🇳

   The decay widths of ${\rm Y}(nS)$ $\to$ ${\bar{d}}^{\ast }(2380)+X$ with $n=1,2,3$ are studied in a phenomenological way. With the help of crossing symmetry, the decay widths are obtained by investigating the imaginary part of the forward scattering amplitudes between $d^{\ast }$ and ${\rm Y}(nS)$. The wave functions of $d^{\ast }$ and deuteron obtained in previous studies are used for calculating the amplitude. The interaction between $d^{\ast }$ ($d$) and ${\rm Y}$ is governed by the quark-meson interaction where the coupling constant is determined by fitting the observed widths of ${\rm Y}(nS)$ $\to$ $\bar{d}+X$. The numerical results show that the decay widths of ${\rm Y}(nS)$ $\to$ ${\bar{d}}^{\ast }+X$ are about $2-10$ times smaller than that of $\bar{d}+X$. The calculated momentum of $\overline{d^{\ast }}$ is in the range $0.3-0.8$ GeV. Therefore, it is very likely that one can find ${\bar{d}}^{\ast }(2380)$ in these semi-inclusive decay processes.

   hep-phnucl-thCPC(2018)·4 citations
6. 06*

   Triangle singularity in $\tau \to f_1(1285)\pi {\nu }_{\tau }$ decay

   E. Oset🇪🇸 · L. Roca🇪🇸

   We show that the ${\tau }^{-}$ decay into $f_1(1285){\pi }^{-}{\nu }_{\tau }$ is dominated by a triangle loop mechanism with $K^{\ast }$, ${\bar{K}}^{\ast }$ and $K$ (or $\bar{K}$) as internal lines, which manifests a strong enhancement reminiscent of a nearby singularity present in the narrow $K^{\ast }$ limit. The $f_1(1285)$ is then produced by its coupling to the $K^{\ast }\bar{K}$ and ${\bar{K}}^{\ast }K$ which is obtained from a previous model where this resonance was dynamically generated as a molecular $K^{\ast }\bar{K}$ (or ${\bar{K}}^{\ast }K$) state using the techniques of the chiral unitary approach. We make predictions for the $f_1\pi$ mass distribution which significantly deviates from the phase-space shape, due to the distortion caused by the triangle singularity. We find a good agreement with the experimental value within uncertainties for the integrated partial decay width, which is a clear indication of the importance of the triangle singularity in this decay and supports the dynamical origin of the $f_1(1285)$ as a $K^{\ast }\bar{K}$ and ${\bar{K}}^{\ast }K$ molecular state.

   hep-phPLB(2018)·24 citations
7. 07*

   Some intriguing aspects of multiparticle production processes

   Grzegorz Wilk🇵🇱 · Zbigniew Włodarczyk🇵🇱

   Multiparticle production processes provide valuable information about the mechanism of the conversion of the initial energy of projectiles into a number of secondaries by measuring their multiplicity distributions and their distributions in phase space. They therefore serve as a reference point for more involved measurements. Distributions in phase space are usually investigated using the statistical approach, very successful in general but failing in cases of small colliding systems, small multiplicities, and at the edges of the allowed phase space, in which cases the underlying dynamical effects competing with the statistical distributions take over. We discuss an alternative approach, which applies to the whole phase space without detailed knowledge of dynamics. It is based on a modification of the usual statistics by generalizing it to a superstatistical form. We stress particularly the scaling and self-similar properties of such an approach manifesting themselves as the phenomena of the log-periodic oscillations and oscillations of temperature caused by sound waves in hadronic matter. Concerning the multiplicity distributions we discuss in detail the phenomenon of the oscillatory behaviour of the modified combinants apparently observed in experimental data.

   hep-phnucl-thInt.J.Mod.Phys.A(2018)·26 citations
8. 08*

   Neutrino mixing in SO(10) GUTs with non-abelian flavor symmetry in the hidden sector

   Alexei Yu. Smirnov🇩🇪 · Xun-Jie Xu🇩🇪

   The relation between the mixing matrices of leptons and quarks: $U_{\mathrm{PMNS}}\approx V_{\mathrm{CKM}}^{†}{U}_0$, where $U_0$ is a matrix of special forms (e.g. BM, TBM), can be a clue for understanding the lepton mixing and neutrino masses. It may imply the Grand unification and existence of a hidden sector with certain symmetry which generates $U_0$ and leads to the smallness of neutrino masses. We apply the residual symmetry approach to obtain $U_0$. The residual symmetries of both the visible and hidden sectors are ${\mathbb{Z}}_2\times {\mathbb{Z}}_2$. Their embedding in a unified flavor group is considered. We find that there are only several possible structures of $U_0$, including the BM mixing and matrices with elements determined by the golden ratio. Realization of the BM scenario based on the $SO(10)$ GUT with the $S_4$ flavor group is presented. Generic features of this scenario are discussed, in particular, the prediction of CP phase $144^{\circ }\lesssim {\delta }_{\mathrm{CP}}\lesssim 210^{\circ }$ in the minimal version.

   hep-phhep-exPRD(2018)·18 citations
9. 09*

   Alternative angular variables for suppression of QCD multijet events in new physics searches with missing transverse momentum at the LHC

   Tai Sakuma🇬🇧 · Henning Flaecher🇬🇧 · Dominic Smith🇬🇧

   We introduce three alternative angular variables-denoted by ${\tilde{\omega }}_{\text{min}}$, ${\hat{\omega }}_{\text{min}}$, and ${\chi }_{\text{min}}$-for QCD multijet event suppression in supersymmetry searches in events with large missing transverse momentum in proton-proton collisions at the LHC at CERN. In searches in all-hadronic final states in the CMS and ATLAS experiments, the angle $\Delta {\phi }_i$, the azimuthal angle between a jet and the missing transverse momentum, is widely used to reduce QCD multijet background events with large missing transverse momentum, which is primarily caused by a jet momentum mismeasurement or neutrinos in hadron decays-the missing transverse momentum is aligned with a jet. A related angular variable-denoted by $\Delta {\phi }_{\text{min}}^{\ast }$, the minimum of the azimuthal angles between a jet and the transverse momentum imbalance of the other jets in the event-is used instead in a series of searches in all-hadronic final states in CMS to suppress QCD multijet background events to a negligible level. In this paper, before introducing the alternative variables, we review the variable $\Delta {\phi }_{\text{min}}^{\ast }$ in detail and identify room for improvement, in particular, to maintain good acceptances for signal models with high jet multiplicity final states. Furthermore, we demonstrate with simulated event samples that ${\hat{\omega }}_{\text{min}}$ and ${\chi }_{\text{min}}$ considerably outperform $\Delta {\phi }_{\text{min}}^{\ast }$ and $\Delta {\phi }_i$ in rejecting QCD multijet background events and that ${\hat{\omega }}_{\text{min}}$ and ${\tilde{\omega }}_{\text{min}}$ are also useful for reducing the total standard model background events.

   hep-ph6 citations
10. 10*

    Precise predictions for same-sign W-boson scattering at the LHC

    Alessandro Ballestrero🇮🇹 · Benedikt Biedermann🇩🇪 · Simon Brass🇩🇪 · Ansgar Denner🇩🇪 · Stefan Dittmaier🇩🇪 · Rikkert Frederix🇩🇪 · Pietro Govoni🇮🇹 · Michele Grossi🇮🇹 · Barbara Jäger🇩🇪 · Alexander Karlberg🇨🇭 · Ezio Maina🇮🇹 · Mathieu Pellen🇩🇪 and 12 other authors

    Vector-boson scattering processes are of great importance for the current run-II and future runs of the Large Hadron Collider. The presence of triple and quartic gauge couplings in the process gives access to the gauge sector of the Standard Model (SM) and possible new-physics contributions there. To test any new-physics hypothesis, sound knowledge of the SM contributions is necessary, with a precision which at least matches the experimental uncertainties of existing and forthcoming measurements. In this article we present a detailed study of the vector-boson scattering process with two positively-charged leptons and missing transverse momentum in the final state. In particular, we first carry out a systematic comparison of the various approximations that are usually performed for this kind of process against the complete calculation, at LO and NLO QCD accuracy. Such a study is performed both in the usual fiducial region used by experimental collaborations and in a more inclusive phase space, where the differences among the various approximations lead to more sizeable effects. Afterwards, we turn to predictions matched to parton showers, at LO and NLO: we show that on the one hand, the inclusion of NLO QCD corrections leads to more stable predictions, but on the other hand the details of the matching and of the parton-shower programs cause differences which are considerably larger than those observed at fixed order, even in the experimental fiducial region. We conclude with recommendations for experimental studies of vector-boson scattering processes.

    hep-phEPJC(2018)·116 citations
11. 11*

    High energy neutrinos

    M. Masip🇪🇸

    We describe several components in the diffuse flux of high energy neutrinos reaching the Earth and discuss whether they could explain IceCube's observations. Then we focus on TeV neutrinos from the Sun. We show that this solar neutrino flux is correlated with the cosmic-ray shadow of the Sun measured by HAWC, and we find that it is much larger than the flux of atmospheric neutrinos. Stars like our Sun provide neutrinos with a very steep spectrum and no associated gammas. We argue that this is the type of contribution that could solve the main puzzle presented by the high energy IceCube data.

    hep-phastro-ph.HE0 citations
12. 12*

    Les Houches 2017: Physics at TeV Colliders Standard Model Working Group Report

    J. Bendavid🇨🇭 · F. Caola🇬🇧 · V. Ciulli🇮🇹 · R. Harlander🇩🇪 · G. Heinrich🇩🇪 · J. Huston🇺🇸 · S. Kallweit🇨🇭 · S. Prestel🇺🇸 · E. Re🇨🇭 · K. Tackmann · J. Thaler🇺🇸 · K. Theofilatos (conveners)🇨🇭 and 93 other authors

    This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators.

    hep-ph171 citations
13. 13*

    A reappraisal of constraints on $Z^{\prime }$ models from unitarity and direct searches at the LHC

    Triparno Bandyopadhyay🇮🇳 · Gautam Bhattacharyya🇮🇳 · Dipankar Das🇮🇳 · Amitava Raychaudhuri🇮🇳

    In a truly model-independent approach, we reexamine a minimal extension of the Standard Model (SM) through the introduction of an additional $U(1)$ symmetry leading to a new neutral gauge boson ($Z^{\prime }$), allowing its kinetic mixing with the hypercharge gauge boson. An SM neutral scalar is used to spontaneously break this extra symmetry leading to the mass of the $Z^{\prime }$. Except for three right-handed neutrinos no other fermions are added. We use the current LHC Drell-Yan data to put model-independent constraints in the parameter space of three quantities, namely, $M_{Z^{\prime }}$, the $Z$-$Z^{\prime }$ mixing angle (${\alpha }_z$) and the extra $U(1)$ effective gauge coupling ($g_x^{\prime }$), which absorb all model dependence. We impose additional constraints from unitarity and low energy neutrino-electron scattering. However, limits extracted from direct searches turn out to be most stringent. We obtain $M_{Z^{\prime }}>4.4$ TeV and $|{\alpha }_z|<0.001$ at $95\%$ C.L., when the strength of the additional $U(1)$ gauge coupling is the same as that of the SM $SU(2{)}_L$.

    hep-phhep-exPRD(2018)·58 citations
14. 14*

    The approach to equilibrium of a quarkonium in a quark-gluon plasma

    Jean-Paul Blaizot🇫🇷 · Miguel Angel Escobedo🇫🇮

    We derive equations of motion for the reduced density matrix of a heavy quarkonium in contact with a quark-gluon plasma in thermal equilibrium. These equations allow in particular a proper treatment of the regime when the temperature of the plasma is comparable to the binding energy of the quarkonium. These equations are used to study how the quarkonium approaches equilibrium with the plasma, and we discuss the corresponding entropy increase, or free energy decrease, depending on the temperature regime. The effect of collisions can be accounted for by the generalization of the imaginary potential introduced in previous studies, and from which collision rates are derived. An important outcome of the present analysis is that this imaginary potential has a sizeable dependence on the energy of the relevant transitions.

    hep-phnucl-thPRD(2018)·103 citations
15. 15*

    Gauge fixing the Standard Model Effective Field Theory

    Andreas Helset🇩🇰 · Michael Paraskevas🇬🇷 · Michael Trott🇩🇰

    We gauge fix the Standard Model Effective Field Theory in a manner invariant under background field gauge transformations using a geometric description of the field connections.

    hep-phPRL(2018)·60 citations
16. 16*

    Saturated Overburden Scattering and the Multiscatter Frontier: Discovering Dark Matter at the Planck Mass and Beyond

    Joseph Bramante🇨🇦 · Benjamin Broerman🇨🇦 · Rafael F. Lang🇺🇸 · Nirmal Raj🇺🇸

    We show that underground experiments like LUX/LZ, PandaX-II, XENON, and PICO could discover dark matter up to the Planck mass and beyond, with new searches for dark matter that scatters multiple times in these detectors. This opens up significant discovery potential via re-analysis of existing and future data. We also identify a new effect which substantially enhances experimental sensitivity to large dark matter scattering cross-sections: while passing through atmospheric or solid overburden, there is a maximum number of scatters that dark matter undergoes, determined by the total number of scattering sites it passes, such as nuclei and electrons. This extends the reach of some published limits and future analyses to arbitrarily large dark matter scattering cross-sections.

    hep-phhep-exPRD(2018)·92 citations
17. 17*

    Magnetic Field Transfer From A Hidden Sector

    Kohei Kamada🇰🇷 · Yuhsin Tsai🇺🇸 · Tanmay Vachaspati🇺🇸

    Primordial magnetic fields in the dark sector can be transferred to magnetic fields in the visible sector due to a gauge kinetic mixing term. We show that the transfer occurs when the evolution of magnetic fields is dominated by dissipation due to finite electric conductivity, and does not occur at later times if the magnetic fields evolve according to magnetohydrodynamics scaling laws. The efficiency of the transfer is suppressed by not only the gauge kinetic mixing coupling but also the ratio between the large electric conductivity and the typical momentum of the magnetic fields. We find that the transfer gives nonzero visible magnetic fields today. However, without possible dynamo amplifications, the field transfer is not efficient enough to obtain the intergalactic magnetic fields suggested by the gamma-ray observations, although there are plenty of possibilities for efficient dark magnetogenesis, which are experimentally unconstrained.

    hep-phastro-ph.COPRD(2018)·10 citations
18. 18*

    $K\to \pi \pi$ and $K-\pi$ Matrix Elements of the Chromomagnetic Operators from Dual QCD

    Andrzej Buras🇩🇪 · Jean-Marc Gerard🇧🇪

    We perform for the first time a direct calculation of on-shell $K\to \pi \pi$ hadronic matrix elements of chromomagnetic operators (CMO) in the Standard Model and beyond. To his end, we use the successful Dual QCD (DQCD) approach in which we also consider off-shell $K-\pi$ matrix elements that allows the comparison with lattice QCD calculations of these matrix elements presented recently by the ETM collaboration. Working in the SU(3) chiral limit, we find for the single $B$ parameter $B_{\mathrm{CMO}}=0.33$. Using the numerical results provided by the ETM collaboration we argue that only small corrections beyond that limit are to be expected. Our results are relevant for new physics scenarios in the context of the emerging ${ϵ}^{\prime }/ϵ$ anomaly strongly indicated within DQCD and supported by RBC-UKQCD lattice collaboration.

    hep-phhep-exhep-latJHEP(2018)·27 citations
19. 19*

    Cannibal Dark Matter and Large Scale Structure

    Manuel A. Buen-Abad🇺🇸 · Razieh Emami🇨🇳 · Martin Schmaltz🇺🇸

    Cannibals are dark matter particles with a scattering process that allows three particles to annihilate to two. This exothermic process keeps the gas of the remaining particles warm long after they become non-relativistic. A cannibalizing dark sector which is decoupled from the Standard Model naturally arises from a pure-glue confining hidden sector. It has an effective field theory description with a single massive interacting real scalar field, the lightest glueball. Since warm dark matter strongly suppresses growth of structure cannibals cannot be all of the dark matter. Thus we propose a scenario where most dark matter is non-interacting and cold but about 1 percent is cannibalistic. We review the cannibals' unusual scaling of the temperature and energy and number densities with redshift and generalize the equations for the growth of matter density perturbations to the case of cannibals. We solve the equations numerically to predict the scaling of the Hubble parameter and the characteristic shape of the linear matter power spectrum as a function of model parameters. Our results may have implications for the ${\sigma }_8$ and $H_0$ problems.

    hep-phastro-ph.COPRD(2018)·60 citations
20. 20*

    Phenomenology of Self-Interacting Dark Matter in a Matter-Dominated Universe

    Nicolás Bernal🇨🇴 · Catarina Cosme🇵🇹 · Tommi Tenkanen🇬🇧

    We study production of self-interacting dark matter (DM) during an early matter-dominated phase. As a benchmark scenario, we consider a model where the DM consists of singlet scalar particles coupled to the visible Standard Model (SM) sector via the Higgs portal. We consider scenarios where the initial DM abundance is set by either the usual thermal freeze-out or an alternative freeze-in mechanism, where DM was never in thermal equilibrium with the SM sector. For the first time, we take the effect of self-interactions within the hidden sector into account in determining the DM abundance, reminiscent to the Strongly Interacting Massive Particle (SIMP) scenario. In all cases, the number density of DM may change considerably compared to the standard radiation-dominated case, having important observational and experimental ramifications.

    hep-phastro-ph.COEPJC(2019)·93 citations
21. 21*

    Homological classification of topological terms in sigma models on homogeneous spaces

    Joe Davighi🇬🇧 · Ben Gripaios🇬🇧

    We classify the topological terms (in a sense to be made precise) that may appear in a non-linear sigma model based on maps from an arbitrary worldvolume manifold to a homogeneous space $G/H$ (where $G$ is an arbitrary Lie group and $H\subset G$). We derive a new condition for $G$-invariance of topological terms, which is necessary and sufficient (at least when $G$ is connected), and discuss a variety of examples in quantum mechanics and quantum field theory. In the present work we discuss only terms that may be written in terms of (possibly only locally-defined) differential forms on $G/H$, leading to an action that is manifestly local. Such terms come in one of two types, with prototypical quantum-mechanical examples given by the Aharonov-Bohm effect and the Dirac monopole. The classification is based on the observation that, for topological terms, the maps from the worldvolume to $G/H$ may be replaced by singular homology cycles on $G/H$. In a forthcoming paper we apply the results to phenomenological models in which the Higgs boson is composite.

    ↳ hep-thhep-phJHEP(2018)·25 citations
22. 22*

    Towards observation of three-nucleon short-range correlations in high Q^2 A(e, e')X reactions

    Donal B. Day Leonid L. Frankfurt · Misak M. Sargsian · Mark I. Strikman

    We present a detailed study of kinematical and dynamical conditions necessary for probing highly elusive three-nucleon short range correlations~(3N-SRCs) in nuclei through inclusive electron scattering. The kinematic requirements that should be satisfied in order to isolate 3N-SRCs in inclusive processes are derived. We demonstrate that a sequence of two short-range NN interactions represents the main mechanism for 3N-SRCs in inclusive processes. Within this mechanism we predict a quadratic dependence of the inclusive cross section ratios of nuclei to ${}^3$He in the 3N-SRC region to the same ratio measured in 2N-SRC domain. The extended analysis of the available data satisfying the necessary 3N-SRC kinematical conditions is presented. This analysis provides tantalizing signatures of scaling associated with the onset of 3N-SRC dominance. The same data are also consistent with the prediction of the quadratic relation between the ratios measured in the 3N and 2N-SRC regions for nuclei ranging $4\le A\le 197$. This agreement made it possible to extract $a_3(A)$, the probability of 3N-SRCs relative to the A=3 nucleus. We find $a_3(A)$ to be significantly larger in magnitude than the analogous parameter, $a_2(A)$, for 2N-SRCs.

    ↳ nucl-thhep-exhep-phnucl-exPRC(2023)·18 citations
23. 23*

    Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN

    D. Banerjee🇺🇸 · V.E. Burtsev🇷🇺 · A. G.Chumakov🇷🇺 · D. Cooke🇨🇭 · P.Crivelli🇨🇭 · E. Depero🇨🇭 · A. V. Dermenev🇷🇺 · S. V. Donskov🇷🇺 · R. R. Dusaev🇷🇺 · T. Enik🇷🇺 · N. Charitonidis🇨🇭 · A. Feshchenko🇷🇺 and 36 other authors

    We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e+e- pairs observed in the excited Be-8 nucleus decays. Due to its coupling to electrons, the X could be produced in the bremsstrahlung reaction e- Z -> e- Z X by a 100 GeV e- beam incident on an active target in the NA64 experiment at the CERN SPS and observed through the subsequent decay into an e+e- pair. With 5.4\times 10^{10} electrons on target, no evidence for such decays was found, allowing to set first limits on the X-e^- coupling in the range 1.3\times 10^{-4} < \epsilon_e < 4.2\times 10^{-4} excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A') from non-observation of the decay A'->e+e- of the bremsstrahlung A' with a mass <~ 23 MeV.

    ↳ hep-exhep-phPRL(2018)·176 citations
24. 24*

    Broadband Axion Dark Matter Haloscopes via Electric Sensing

    Ben T. McAllister🇦🇺 · Maxim Goryachev🇦🇺 · Jeremy Bourhill🇦🇺 · Eugene N. Ivanov🇦🇺 · Michael E. Tobar🇦🇺

    The mass of axion dark matter is only weakly bounded by cosmological observations, necessitating a variety of detection techniques over several orders of magnitude of mass ranges. Axions haloscopes based on resonant cavities have become the current standard to search for dark matter axions. Such structures are inherently narrowband and for low masses the volume of the required cavity becomes prohibitively large. Broadband low-mass detectors have already been proposed using inductive magnetometer sensors and a gapped toroidal solenoid magnet. In this work we propose an alternative, which uses electric sensors in a conventional solenoidal magnet aligned in the laboratory z-axis, as implemented in standard haloscope experiments. In the presence of the DC magnetic field, the inverse Primakoff effect causes a time varying permanent electric vacuum polarization in the z-direction to oscillate at the axion Compton frequency, which induces an oscillating electromotive force. We propose non-resonant techniques to detect this oscillating elctromotive force by implementing a capacitive sensor or an electric dipole antenna coupled to a low noise amplifier. We present the first experimental results and discuss the foundations and potential of this proposal. Preliminary results constrain $g_{a\gamma \gamma }>\sim 2.35\times 10^{-12}$ ${\text{GeV}}^{-1}$ in the mass range of $2.08\times 10^{-11}$ to $2.2\times 10^{-11}$ eV, and demonstrate potential sensitivity to axion-like dark matter with masses in the range of $10^{-12}$ to $10^{-8}$ eV.

    ↳ physics.ins-detgr-qchep-exhep-ph37 citations
25. 25*

    The Ultraviolet Behavior Of Quantum Gravity

    Damiano Anselmi🇮🇹 · Marco Piva🇮🇹

    A theory of quantum gravity has been recently proposed by means of a novel quantization prescription, which is able to turn the poles of the free propagators that are due to the higher derivatives into fakeons. The classical Lagrangian contains the cosmological term, the Hilbert term, $\sqrt{-g}{R}_{\mu \nu }{R}^{\mu \nu }$ and $\sqrt{-g}{R}^2$. In this paper, we compute the one-loop renormalization of the theory and the absorptive part of the graviton self energy. The results illustrate the mechanism that makes renormalizability compatible with unitarity. The fakeons disentangle the real part of the self energy from the imaginary part. The former obeys a renormalizable power counting, while the latter obeys the nonrenormalizable power counting of the low energy expansion and is consistent with unitarity in the limit of vanishing cosmological constant. The value of the absorptive part is related to the central charge $c$ of the matter fields coupled to gravity.

    ↳ hep-thgr-qchep-phJHEP(2018)·108 citations
26. 26*

    Millisecond Pulsars, TeV Halos, and Implications For The Galactic Center Gamma-Ray Excess

    Dan Hooper🇺🇸 · Tim Linden🇺🇸

    Observations by HAWC indicate that many young pulsars (including Geminga and Monogem) are surrounded by spatially extended, multi-TeV emitting regions. It is not currently known, however, whether TeV emission is also produced by recycled, millisecond pulsars (MSPs). In this study, we perform a stacked analysis of 24 MSPs within HAWC's field-of-view, finding between 2.6-3.2 sigma evidence that these sources are, in fact, surrounded by TeV halos. The efficiency with which these MSPs produce TeV halos is similar to that exhibited by young pulsars. This result suggests that several dozen MSPs will ultimately be detectable by HAWC, including many "invisible" pulsars without radio beams oriented in our direction. The TeV halos of unresolved MSPs could also dominate the TeV-scale diffuse emission observed at high galactic latitudes. We also discuss the possibility that TeV and radio observations could be used to constrain the population of MSPs that is present in the inner Milky Way, thereby providing us with a new way to test the hypothesis that MSPs are responsible for the Galactic Center GeV excess.

    ↳ astro-ph.HEastro-ph.COhep-phPRD(2018)·49 citations
27. 27*

    The Penrose process, superradiance and ergoregion instabilities

    Rodrigo Vicente🇵🇹 · Vitor Cardoso🇵🇹 · Jorge C. Lopes🇵🇹

    Superradiant scattering is a radiation enhancement process that takes place in many contexts, and which has recently found exciting applications in astro and particle physics. In the framework of curved spacetime physics, it has been associated with the classical Penrose process for particles. Superradiance is usually also associated with bosonic fields around geometries with ergoregions and horizons. These notions are in clear tension however: the Penrose process occurs for horizonless geometries, and particles are composed of fermions. Here, we resolve the tension in its different aspects, by showing that (i) superradiance occurs for self-interacting fermions on flat spacetime; (ii) superradiance occurs also for horizonless geometries, where it leads to an ergoregion instability. Ultracompact, horizonless geometries will usually respond with echoes of growing amplitude, until rotational (or electrostatic) energy is extracted from the object; (iii) the Fourier-domain analysis leads to absence of superradiance when horizons are not present. We elucidate why this analysis fails to give meaningful results; (iv) finally, we show that superradiant, ergoregion instabilities have a particle analog of similar growth timescales and which can power the formation of a structure outside a compact, rotating star.

    ↳ gr-qcastro-ph.HEhep-phhep-thPRD(2018)·59 citations

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