Mon·Jul 1, 2019Monday·July 1, 2019

1. 01*

   A numerical evaluation of planar two-loop helicity amplitudes for a W-boson plus four partons

   Heribertus Bayu Hartanto🇬🇧 · Simon Badger🇬🇧 · Christian Brønnum-Hansen🇬🇧 · Tiziano Peraro🇨🇭

   We present the first numerical results for the two-loop helicity amplitudes for the scattering of four partons and a W-boson in QCD. We use a finite field sampling method to reduce directly from Feynman diagrams to the coefficients of a set of master integrals after applying integration-by-parts identities. Since the basis of master integrals is not yet fully known analytically, we identify a set of master integrals with a simple divergence structure using local numerator insertions. This allows for accurate numerical evaluation of the amplitude using sector decomposition methods.

   hep-phhep-thJHEP(2019)·66 citations
2. 02*

   Testability of leptogenesis with three RH-neutrinos below the electroweak scale

   Michele Lucente🇧🇪

   The Standard Model extended with right-handed neutrinos whose masses are below the electroweak scale provides a simultaneous solution for the origin of neutrino masses and of the baryon asymmetry of the Universe, that can be tested in current experiments. If three right-handed neutrinos participate to the processes, their parameter space of solutions extends to very large mixing angles, saturating the current experimental constraints. Solutions with right-handed neutrino masses at the GeV scale can be probed in the decay of $B$ mesons at the LHC. For this channel the collision of isotopes of intermediate mass such as Ar provides a better sensitivity per unit of running time compared to collisions with protons.

   hep-phhep-ex0 citations
3. 03*

   Are the XYZ states unconventional states or conventional states with unconventional properties?

   Christoph Hanhart🇩🇪 · Eberhard Klempt🇩🇪

   We discuss three possible scenarios for the interpretation of mesons containing a heavy quark and its antiquark near and above the first threshold for a decay into a pair of heavy mesons in a relative $S$--wave. View I assumes that these thresholds force the quark potential to flatten which implies that while in these energy ranges molecular states may be formed there should not be any quark--anti-quark states above these thresholds. View II assumes that the main part of the interaction between two mesons is due to the poles which originate from the $Q\bar{Q}$ interaction. The properties of the $Q\bar{Q}$ mesons are strongly influenced by opening thresholds but the number of states is given by the quark model. In View III, both types of mesons are admitted also near and above the open flavor thresholds: $Q\bar{Q}$ mesons and dynamically generated mesons. Experimental consequences of these different views are discussed.

   hep-phhep-exInt.J.Mod.Phys.A(2020)·18 citations
4. 04*

   $DK$, $DDK$, and $DDDK$ molecules--understanding the nature of the $D_{s0}^{\ast }(2317)$

   Tian-Wei Wu🇨🇳 · Ming-Zhu Liu🇨🇳 · Li-Sheng Geng🇨🇳 · Emiko Hiyama🇯🇵 · Manuel Pavon Valderrama🇨🇳

   The $DK$ interaction is strong enough to form a bound state, the $D_{s0}^{\ast }(2317)$. This in turn begs the question of whether there are bound states composed of several charmed mesons and a kaon. Previous calculations indicate that the three-body $DDK$ system is probably bound, where the quantum numbers are $J^P=0^{-}$, $I=\frac{1}{2}$, $S=1$ and $C=2$. The minimum quark content of this state is $cc\bar{q}\bar{s}$ with $q=u,d$, which means that, if discovered, it will be an explicitly exotic tetraquark. In the present work. we apply the Gaussian Expansion Method to study the $DDDK$ system and show that it binds as well. The existence of these three and four body states is rather robust with respect to the $DD$ interaction and subleading (chiral) corrections to the $DK$ interaction. If these states exist, it is quite likely that their heavy quark symmetry counterparts exist as well. These three-body $DDK$ and four-body $DDDK$ molecular states could be viewed as counterparts of atomic nuclei, which are clusters of nucleons bound by the residual strong force, or chemical molecules, which are clusters of atoms bound by the residual electromagnetic interaction.

   hep-phhep-exhep-latnucl-ex+1PRD(2019)·68 citations
5. 05*

   30 years of jet quenching

   Xin-Nian Wang🇨🇳

   In the last 30 years, the physics of jet quenching has gone from an early stage of a pure theoretical idea to initial theoretical calculations, experimental verification and now a powerful diagnostic tool for studying properties of the quark-gluon plasma (QGP) in high-energy heavy-ion collisions. I will describe my collaboration with Miklos Gyulassy in this exciting area of high-energy nuclear physics in the past 30 years on this special occasion of his 70th birthday and discuss what is ahead of us in jet tomographic study of QGP in heavy-ion collisions.

   hep-phnucl-thPoS(2020)·5 citations
6. 06*

   Low scale leptogenesis in a hybrid model of the scotogenic type I and III seesaw

   Daijiro Suematsu🇯🇵

   The scotogenic type I and type III seesaw models are good candidates to explain the existence of neutrino masses and dark matter simultaneously. However, since triplet fermions have SU(2) gauge interaction, they cannot be out of equilibrium before the electroweak symmetry breaking. Thus, leptogenesis seems to be difficult within a framework of the pure type III seesaw model. Some extension seems to be required to solve this fault. A model extended by introducing a singlet fermion could be such a simple example. If the singlet fermion is in the thermal equilibrium even for its extremely small neutrino Yukawa coupling, leptogenesis could be shown to occur successfully for a rather low mass of the singlet fermion. The required mass could be lowered to $10^4$~GeV.

   hep-phPRD(2019)·18 citations
7. 07*

   Borexino and General Neutrino Interactions

   Amir N. Khan🇩🇪 · Werner Rodejohann🇩🇪 · Xun-Jie Xu🇩🇪

   We derive constraints on all possible general neutrino-electron interactions (scalar, vector, pseudoscalar, axialvector and tensor) using the recent real time Borexino event rate measurements of $pp$, $pep$ and ${}^{7}Be$ solar neutrinos. The limits improve several previous ones from TEXONO and CHARM-II for incoming electron and muon neutrinos, and are the first ones for the tau flavor. Future improvements by next-generation solar neutrino experiments are also studied. The limits extend the physics reach of solar neutrino measurements to TeV-scale physics. Finally, the different properties of the new interactions for Dirac and Majorana neutrinos are discussed.

   hep-phhep-exPRD(2020)·51 citations
8. 08*

   Kinetic approach to a relativistic BEC with inelastic processes

   Richard Lenkiewicz🇩🇪 · Alex Meistrenko🇩🇪 · Hendrik van Hees🇩🇪 · Kai Zhou🇩🇪 · Zhe Xu🇨🇳 · Carsten Greiner🇩🇪

   The phenomenon of Bose-Einstein condensation is investigated in the context of the Color-Glass-Condensate description of the initial state of ultrarelativistic heavy-ion collisions. For the first time, in this paper we study the influence of particle-number changing $2\leftrightarrow 3$ processes on the transient formation of a Bose-Einstein Condensate within an isotropic system of scalar bosons by including $2\leftrightarrow 3$ interactions of massive bosons with constant and isotropic cross sections, following a Boltzmann equation. The one-particle distribution function is decomposed in a condensate part and a non-zero momentum part of excited modes, leading to coupled integro-differential equations for the time evolution of the condensate and phase-space distribution function, which are then solved numerically. Our simulations converge to the expected equilibrium state, and only for ${\sigma }_{23}/{\sigma }_{22}\ll 1$ we find that a Bose-Einstein condensate emerges and decays within a finite lifetime in contrast to the case where only binary scattering processes are taken into account, and the condensate is stable due to particle-number conservation. Our calculations demonstrate that Bose-Einstein Condensates in the very early stage of heavy-ion collisions are highly unlikely, if inelastic collisions are significantly participating in the dynamical gluonic evolution.

   hep-phnucl-thPRD(2019)·6 citations
9. 09*

   Non-derivative Axionic Couplings to Nucleons at large and small N

   Francesco Bigazzi🇮🇹 · Aldo L. Cotrone🇮🇹 · Matti Järvinen🇳🇱 · Elias Kiritsis🇬🇷

   Among the possible CP-odd couplings of the axion to ordinary matter, the most relevant ones for phenomenology are the Yukawa couplings to nucleons. We analyze such non-derivative couplings within three different approaches: standard effective field theory, the Skyrme model and holographic QCD. In all the cases, the couplings can be related to the CP-odd non-derivative couplings to nucleons of the low-lying mesons and the ${\eta }^{\prime }$. Using the effective field theory approach we discuss how to derive the expressions for the CP-odd interaction terms as functions of the parameters of the effective Lagrangian at generic number of colors $N_c$ and flavors $N_f$. Then, we compute the CP-odd couplings to nucleons of the axion, the ${\eta }^{\prime }$ and the pseudo-Goldstone mesons in both the Skyrme and the holographic QCD model with $N_f=2,3$. We present model-independent expressions for the coefficients of the non-derivative axion-nucleon couplings. This allows us to provide quantitative estimates of these couplings.

   hep-phhep-lathep-thJHEP(2020)·23 citations
10. 10*

    Neutrino decoherence in presence of strong gravitational fields

    Amélie Chatelain🇫🇷 · Maria Cristina Volpe🇫🇷

    We explore the impact of strong gravitational fields on neutrino decoherence. To this aim, we employ the density matrix formalism to describe the propagation of neutrino wave packets in curved spacetime. By considering Gaussian wave packets, we determine the coherence proper time, neglecting the effect of matter outside the compact object. We show that strong gravitational fields nearby compact objects significantly influence neutrino coherence.

    hep-phastro-ph.SRhep-thPLB(2020)·31 citations
11. 11*

    Proposal for the validation of Monte Carlo implementations of the standard model effective field theory

    Gauthier Durieux (ed.)🇮🇱 · Ilaria Brivio (ed.)🇩🇰 · Fabio Maltoni (ed. ex officio)🇧🇪 · Michael Trott (ed. ex officio)🇩🇰 · Simone Alioli🇮🇹 · Andy Buckley🇬🇧 · Mauro Chiesa🇩🇪 · Jorge de Blas🇮🇹 · Athanasios Dedes🇬🇷 · Céline Degrande🇧🇪 · Ansgar Denner🇩🇪 · Christoph Englert🇬🇧 and 29 other authors

    We propose a procedure to cross-validate Monte Carlo implementations of the standard model effective field theory. It is based on the numerical comparison of squared amplitudes computed at specific phase-space and parameter points in pairs of implementations. Interactions are fully linearised in the effective field theory expansion. The squares of linear effective field theory amplitudes and their interference with standard-model contributions are compared separately. Such pairwise comparisons are primarily performed at tree level and a possible extension to the one-loop level is also briefly considered. We list the current standard model effective field theory implementations and the comparisons performed to date.

    hep-phhep-ex12 citations
12. 12*

    Metastable Nuclear Isomers as Dark Matter Accelerators

    Maxim Pospelov🇨🇦 · Surjeet Rajendran🇺🇸 · Harikrishnan Ramani🇺🇸

    Inelastic dark matter and strongly interacting dark matter are poorly constrained by direct detection experiments since they both require the scattering event to deliver energy from the nucleus into the dark matter in order to have observable effects. We propose to test these scenarios by searching for the collisional de-excitation of meta-stable nuclear isomers by the dark matter particles. The longevity of these isomers is related to a strong suppression of $\gamma$- and $\beta$-transitions, typically inhibited by a large difference in the angular momentum for the nuclear transition. The collisional de-excitation by dark matter is possible since heavy dark matter particles can have a momentum exchange with the nucleus comparable to the inverse nuclear size, hence lifting tremendous angular momentum suppression of the nuclear transition. This de-excitation can be observed either by searching for the direct effects of the decaying isomer, or through the re-scattering or decay of excited dark matter states in a nearby conventional dark matter detector setup. Existing nuclear isomer sources such as naturally occurring ${}^{180m}$Ta, ${}^{137m}$Ba produced in decaying Cesium in nuclear waste, ${}^{177m}$Lu from medical waste, and ${}^{178m}$Hf from the Department of Energy storage can be combined with current dark matter detector technology to search for this class of dark matter.

    hep-phastro-ph.COhep-exnucl-ex+1PRD(2020)·48 citations
13. 13*

    Probing Quadratic Gravity with Binary Inspirals

    Yunho Kim🇦🇺 · Archil Kobakhidze🇦🇺 · Zachary S. C. Picker🇦🇺

    In this paper, we study gravitational waves generated by binary systems within an extension of General Relativity which is described by the addition of quadratic in curvature tensor terms to the Einstein-Hilbert action. Treating quadratic gravity as an effective theory valid in the low energy/curvature regime, we argue that reliable calculations can be performed in the early inspiral phase, and furthermore, no flux of additional massive waves can be detected. We then compute the massive dipole (-1PN) leading corrections to the post-Newtonian (PN) expansion of the standard waveform. By confronting these theoretical calculations with available experimental data, we constrain both unknown parameters of quadratic gravity to be $0\le \gamma \lesssim 5.7\cdot 10^{76}$, and $-\frac{\gamma }{4}\le \beta \lesssim -4.2\cdot 10^{75}$.

    ↳ gr-qchep-phhep-thEPJC(2021)·16 citations
14. 14*

    Non-Fierz-Pauli bimetric theory from quadratic curvature gravity on Einstein manifolds

    Yuki Niiyama🇯🇵 · Yuya Nakamura🇯🇵 · Ryosuke Zaimokuya🇯🇵 · Yu Furuya🇯🇵 · Yuuiti Sendouda🇯🇵

    We show that, in four-dimensional spacetimes with an arbitrary Einstein metric, with and without a cosmological constant, perturbative dynamical degrees of freedom in generic quadratic-curvature gravity can be decoupled into massless and massive parts. The massive part has the structure identical to, modulo the over-all sign, the non-Fierz-Pauli-type massive gravity, and a further decomposition into the spin-2 and spin-0 sectors can be done. The equivalence at the level of equations of motion allows us to translate various observational bounds on the mass of extra fields into constraints on the coupling constants in quadratic curvature gravity. We find that the Weyl-squared term is confronting two apparently contradicting constraints on massive spin-2 fields from the inverse-square law experiments and observations of spinning black holes.

    ↳ gr-qchep-phhep-th2 citations
15. 15*

    The Holographic QCD Axion

    Francesco Bigazzi🇮🇹 · Alessio Caddeo🇮🇹 · Aldo L. Cotrone🇮🇹 · Paolo Di Vecchia🇩🇰 · Andrea Marzolla🇮🇹

    A holographic model of QCD axion is presented. It describes a composite axion in the KSVZ class. Having a gravity dual, based on the Witten-Sakai-Sugimoto model, it is calculable in the strongly coupled regime. Its basic properties are derived, including the low energy Lagrangian, from which the axion couplings to nucleons can be derived. Basic features in the deconfined phase are studied as well. In particular, the temperature dependence of the axion mass is extracted from the topological susceptibility. As an aside, the topological susceptibility of strongly coupled $\mathcal{N}=4$ SYM at finite temperature is derived for the first time.

    ↳ hep-thhep-phJHEP(2019)·22 citations
16. 16*

    The Hunt for Primordial Interactions in the Large Scale Structures of the Universe

    Matteo Biagetti🇳🇱

    The understanding of the primordial mechanism that seeded the cosmic structures we observe today in the sky is one of the major goals in cosmology. The leading paradigm for such a mechanism is provided by the inflationary scenario, a period of violent accelerated expansion in the very early stages of evolution of the Universe. While our current knowledge of the physics of inflation is limited to phenomenological models which fit observations, an exquisite understanding of the particle content and interactions taking place during inflation would provide breakthroughs in our understanding of fundamental physics at high energies. In this review, we summarize recent theoretical progress in the modelling of the imprint of primordial interactions in the large scale structures of the Universe. We focus specifically on the effects of such interactions on the statistical distribution of dark matter halos, providing a consistent treatment of the steps required to connect the correlations generated among fields during inflation all the way to the late-time correlations of halos.

    ↳ astro-ph.COhep-phhep-thGalaxies(2019)·67 citations
17. 17*

    Astrophysical neutrinos: theory

    Ofelia Pisanti🇮🇹

    In the era of multi-messenger astronomy, neutrinos are among the most important astronomical messengers, due to their interaction properties. In these lessons I briefly review the main issues concerning the theory on astrophysical neutrinos.

    ↳ astro-ph.COastro-ph.HEhep-phJ.Phys.Conf.Ser.(2019)·8 citations
18. 18*

    A Mellin Space Approach to Cosmological Correlators

    Charlotte Sleight🇺🇸

    We propose a Mellin space approach to the evaluation of late-time momentum-space correlation functions of quantum fields in $\left(d+1\right)$-dimensional de Sitter space. The Mellin-Barnes representation makes manifest the analytic structure of late-time correlators and, more generally, provides a convenient general $d$ framework for the study of conformal correlators in momentum space. In this work we focus on tree-level correlation functions of general scalars as a prototype, including $n$-point contact diagrams and $4$-point exchanges. For generic scalars, both the contact and exchange diagrams are given by (generalised) Hypergeometric functions, which reduce to existing expressions available in the literature for $d=3$ and external scalars which are either simultaneously conformally coupled or massless. This approach can also be used for the perturbative bulk evaluation of momentum-space boundary correlators in $\left(d+1\right)$-dimensional anti-de Sitter space (Witten diagrams).

    ↳ hep-thastro-ph.COhep-phJHEP(2020)·220 citations
19. 19*

    Suppression of elliptic flow without viscosity

    Adam Takacs🇳🇴 · Denes Molnar🇭🇺

    We investigate fluid-to-particle conversion using the usual Cooper-Frye approach but with more general local equilibrium distributions than the Boltzmann or Bose/Fermi distributions typically used. Even though we study ideal fluids (i.e., shear stress and bulk pressure are zero everywhere), we find a suppression of elliptic flow (v2) at high transverse momenta (pT>1.5 GeV/c), relative to results obtained with the traditional Boltzmann distributions. The non-viscous suppression shows qualitatively similar features to the well-known shear viscous suppression of v2; for example, it increases with pT, and it is smaller for heavier species as seen in self-consistent kinetic theory calculations. Our results question whether all of the v2 suppression seen in the data can be attributed to viscous effects, and indicate that shear viscosities extracted from RHIC and LHC elliptic flow data might be overestimated.

    ↳ nucl-thhep-exhep-phnucl-ex8 citations
20. 20*

    How AMPT generates large elliptic flow with small cross sections

    Denes Molnar (Dept. of Physics and Astronomy, Purdue University, West Lafayette, IN)🇺🇸

    We resolve the long-standing open question of how the transport model AMPT manages to generate sufficiently high elliptic flow (v2) in A+A reactions with only few-millibarn 2->2 partonic cross sections - in apparent contradiction with an early study by Molnar and Gyulassy. Through detailed comparisons with the covariant Molnar's Parton Cascade (MPC), we pinpoint which features of initial conditions, interactions, and dynamics encoded in the partonic stage of AMPT allow it to circumvent the "opacity puzzle" at RHIC.

    ↳ nucl-thhep-phnucl-ex9 citations
21. 21*

    A Trigger for Displaced Muon Pairs Following the CMS Phase II Upgrades

    Yuri Gershtein🇺🇸 · Simon Knapen🇺🇸

    We show that the phase II upgrade of the CMS tracking detector could enable the experiment to trigger on very low mass $\mathcal{O}(1\text{GeV})$ displaced muon pairs with minimal $p_T$ cuts. As a result, CMS can be competitive with LHCb when searching for low mass displaced exotics originating from heavy flavor decays. The method can also be applied to signatures without muons but with a moderate amount of MET, $H_T$ or multiple displaced vertices in the event.

    ↳ hep-exhep-phPRD(2020)·15 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.