Wed·Nov 7, 2018Wednesday·November 7, 2018

1. 01*

   Nuclear PDFs Today

   Hannu Paukkunen🇫🇮

   I review the current status of global analysis of nuclear parton distributions and discuss some near-future prospects. I also advocate proton-nucleus (p-$A$) measurements at the LHC with $A\ll 208$ from the viewpoint of nuclear parton distributions.

   hep-phPoS(2018)·26 citations
2. 02*

   Heavy flavour production in the SACOT-$m_{\mathrm{T}}$ scheme

   Ilkka Helenius🇫🇮 · Hannu Paukkunen🇫🇮

   The hadroproduction of heavy-flavoured mesons has recently attracted a growing interest e.g. within the people involved in global analysis of proton and nuclear parton distribution functions, saturation physics, and physics of cosmic rays. In particular, the D- and B-meson measurements of LHCb at forward direction are sensitive to gluon dynamics at small $x$ and are one of the few perturbative small-$x$ probes before the next generation deep-inelastic-scattering experiments. In this talk, we will concentrate on the collinear-factorization approach to inclusive D-meson production and describe a novel implementation - SACOT-$m_{\mathrm{T}}$ - of the general-mass variable flavour number scheme (GM-VFNS). In the GM-VFNS framework the cross sections retain the full heavy-quark mass dependence at $p_{\mathrm{T}}=0$, but gradually reduce to the ordinary zero-mass results towards asymptotically high $p_{\mathrm{T}}$. However, the region of small (but non-zero) $p_{\mathrm{T}}$ has been somewhat problematic in the previous implementations of GM-VFNS, leading to divergent cross sections towards $p_{\mathrm{T}}\to 0$, unless the QCD scales are set in a particular way. Here, we provide a solution to this problem. In essence, the idea is to consistently account for the underlying energy-momentum conservation in the presence of a final-state heavy quark-antiquark pair. This automatically leads to a well-behaved GM-VFNS description of the cross sections across all $p_{\mathrm{T}}$ without a need to fine tune the QCD scales. The results are compared with the LHCb data and a very good agreement is found. We also compare to fixed-order based calculations and explain why they lead to approximately a factor of two lower D-meson production cross sections than the GM-VFNS approach.

   hep-phPoS(2018)·1 citation
3. 03*

   Calibrating the Naïve Cornell Model with NRQCD

   Vicent Mateu🇪🇸 · Pablo G. Ortega🇪🇸 · David R. Entem🇪🇸 · Francisco Fernandez🇪🇸

   Along the years, the Cornell Model has been extraordinarily successful in describing hadronic phenomenology, in particular in physical situations for which an effective theory of the strong interactions such as NRQCD cannot be applied. As a consequence of its achievements, a relevant question is whether its model parameters can somehow be related to fundamental constants of QCD. We shall give a first answer in this article by comparing the predictions of both approaches. Building on results from a previous study on heavy meson spectroscopy, we calibrate the Cornell model employing NRQCD predictions for the lowest-lying bottomonium states up to N${}^3$LO, in which the bottom mass is varied within a wide range. We find that the Cornell model mass parameter can be identified, within perturbative uncertainties, with the MSR mass at the scale $R=1$GeV. This identification holds for any value of ${\alpha }_s$ or the bottom mass, and for all perturbative orders investigated. Furthermore, we show that: a) the "string tension" parameter is independent of the bottom mass, and b) the Coulomb strength $\kappa$ of the Cornell model can be related to the QCD strong coupling constant ${\alpha }_s$ at a characteristic non-relativistic scale. We also show how to remove the $u=1/2$ renormalon of the static QCD potential and sum-up large logs related to the renormalon subtraction by switching to the low-scale, short-distance MSR mass, and using R-evolution. Our R-improved expression for the static potential remains independent of the heavy quark mass value and agrees with lattice QCD results for values of the radius as large as $0.8$fm, and with the Cornell model potential at long distances. Finally we show that for moderate values of $r$, the R-improved NRQCD and Cornell static potentials are in head-on agreement.

   hep-phhep-latEPJC(2019)·42 citations
4. 04*

   Long-Lived Fermions at AL3X

   Daniel Dercks🇩🇪 · Herbert K. Dreiner🇩🇪 · Martin Hirsch🇪🇸 · Zeren Simon Wang🇩🇪

   Recently Gligorov $\text{et al.}$ [arXiv:1810.03636] proposed to build a cylindrical detector named '$\text{AL3X}$' close to the $\text{ALICE}$ experiment at interaction point (IP) 2 of the LHC, aiming for discovery of long-lived particles (LLPs) during Run 5 of the HL-LHC. We investigate the potential sensitivity reach of this detector in the parameter space of different new-physics models with long-lived fermions namely heavy neutral leptons (HNLs) and light supersymmetric neutralinos, which have both not previously been studied in this context. Our results show that the $\text{AL3X}$ reach can be complementary or superior to that of other proposed detectors such as $\text{CODEX-b}$, $\text{FASER}$, $\text{MATHUSLA}$ and $\text{SHiP}$.

   hep-phPRD(2019)·85 citations
5. 05*

   WIMPy Leptogenesis in extended Scotogenic Model

   Debasish Borah🇮🇳 · Arnab Dasgupta🇰🇷 · Sin Kyu Kang🇰🇷

   We address the possibility of realizing successful leptogenesis from dark matter annihilations in the scotogenic model of neutrino masses to explain the same order of magnitude abundance of dark matter and baryons in the present Universe. After showing that the minimal model in this category cannot satisfy all these requirements, we study a minimal extension of this model and find that the scale of leptogenesis can be as low as 5 TeV, lower than the one in vanilla leptogenesis scenario in scotogenic model along with the additional advantage of explaining the baryon-dark matter coincidence. Due to such low scale, the model remains predictive at dark matter direct detection and rare decay experiments looking for charged lepton flavor violating processes.

   hep-phPoS(2019)·2 citations
6. 06*

   Study of $CP$ Violation in $B^{-}\to K^{-}{\pi }^{+}{\pi }^{-}$ and $B^{-}\to K^{-}\sigma (600)$ decays in the QCD factorization approach

   Jing-Juan Qi🇨🇳 · Zhen-Yang Wang🇨🇳 · Xin-Heng Guo🇨🇳 · Zhen-Hua Zhang🇨🇳 · Chao Wang🇨🇳

   In this work, we study the localized $CP$ violation in $B^{-}\to K^{-}{\pi }^{+}{\pi }^{-}$ and $B^{-}\to K^{-}\sigma (600)$ decays by employing the quasi two-body QCD factorization approach. Both the resonance and the nonresonance contributions are studied for the $B^{-}\to K^{-}{\pi }^{+}{\pi }^{-}$ decay. The resonance contributions include those not only from $[\pi \pi ]$ channels including $\sigma (600)$, ${\rho }^0(770)$ and $\omega (782)$ but also from $[K\pi ]$ channels including $K^{\ast }(892)$, $K_0^{\ast }(1430)$, $K^{\ast }(1410)$, $K^{\ast }(1680)$ and $K_2^{\ast }(1430)$. By fitting the experimental data ${\mathcal{A}}_{\mathcal{C}\mathcal{P}}(K^{-}{\pi }^{+}{\pi }^{-})=0.678\pm 0.078\pm 0.0323\pm 0.007$ for $m_{K^{-}{\pi }^{+}}^2<15$ ${\mathrm{GeV}}^2$ and $0.08<m_{{\pi }^{+}{\pi }^{-}}^2<0.66$ ${\mathrm{GeV}}^2$, we get the end-point divergence parameters in our model, ${\varphi }_S\in [4.75,5.95]$ and ${\rho }_S\in [4.2,8]$. Using these results for ${\rho }_S$ and ${\varphi }_S$, we predict that the $CP$ asymmetry parameter ${\mathcal{A}}_{\mathcal{C}\mathcal{P}}\in [-0.094,-0.034]$ and the branching fraction $\mathcal{B}\in [1.82,20.0]\times 10^{-5}$ for the $B^{-}\to K^{-}\sigma (600)$ decay. In addition, we also analyse contributions to the localized $CP$ asymmetry ${\mathcal{A}}_{\mathcal{C}\mathcal{P}}(B^{-}\to K^{-}{\pi }^{+}{\pi }^{-})$ from $[\pi \pi ]$, $[K\pi ]$ channel resonances and nonresonance individually, which are found to be ${\mathcal{A}}_{\mathcal{C}\mathcal{P}}(B^{-}\to K^{-}[{\pi }^{+}{\pi }^{-}]\to K^{-}{\pi }^{+}{\pi }^{-})=0.585\pm 0.045$, ${\mathcal{A}}_{\mathcal{C}\mathcal{P}}(B^{-}\to [K^{-}{\pi }^{+}]\pi \to K^{-}{\pi }^{+}{\pi }^{-})=0.086\pm 0.021$ and ${{\mathcal{A}}_{\mathcal{C}\mathcal{P}}}^{NR}(B^{-}\to K^{-}{\pi }^{+}{\pi }^{-})=0.061\pm 0.0042$, respectively. Comparing these results, we can see that the localized $CP$ asymmetry in the $B^{-}\to K^{-}{\pi }^{+}{\pi }^{-}$ decay is mainly induced by the $[\pi \pi ]$ channel resonances while contributions from the $[K\pi ]$ channel resonances and nonresonance are both very small.

   hep-phPRD(2019)·29 citations
7. 07*

   Weak Decays of Doubly Heavy Baryons: W-Exchange

   Qi-An Zhang🇨🇳

   Since the LHCb collaboration announced the observation of the doubly charmed baryon ${\Xi }_{cc}^{++}$, a series of studies of doubly heavy baryons have been presented. In this work, I analyse the non-leptonic weak decays of doubly heavy baryons ${\Xi }_{bc}$ and ${\Omega }_{bc}$ under the flavor $SU(3)$ symmetry. I mainly focus on the $W$-exchange diagrams, which will contribute to the decay channels with final states are light meson and light baryon. These channels would be helpful for searching for ${\Xi }_{bc}$ and ${\Omega }_{bc}$ at LHC. And these channels and relations of corresponding decay widths could be examined by the future experimental facilities such as LHC, Belle II and CEPC.

   hep-phEPJC(2018)·36 citations
8. 08*

   Unearthing the electroweak structure of warped 5D models

   Abhishek M. Iyer🇮🇹 · K. Sridhar🇮🇳

   Heavy charged bosons, with masses in the range of a few TeV, are a characteristic of warped extra-dimensional models with bulk gauge fields. Rendering the latter consistent with electroweak precision tests typically requires either a deformation of the metric or extension of the gauge symmetry. We make here the first attempt at finding empirical discriminants which would tell these models apart. Demonstrating the power of simple kinematic observables involving same-sign leptons, we construct simple yet powerful statistical discriminants.

   hep-phPRD(2019)·1 citation
9. 09*

   Heavy baryon spectroscopy

   R.N. Faustov🇷🇺 · V.O. Galkin🇷🇺

   Masses of heavy baryons are calculated in the relativistic quark-diquark picture. Obtained results are in good agreement with available experimental data including recent measurements by the LHCb Collaboration. Possible quantum numbers of excited heavy baryon states are discussed.

   hep-phEPJ Web Conf.(2019)·11 citations
10. 10*

    Constraining the anomalous Higgs boson coupling in $H$+$\gamma$ production

    Liaoshan Shi🇨🇳 · Zhijun Liang🇨🇳 · Bo Liu🇨🇳 · Zhenhui He🇨🇳

    Higgs boson production in association with a photon ($H$+$\gamma$) offers a promising channel to test the Higgs boson to photon coupling at various energy scales. Its potential sensitivity to anomalous couplings of the Higgs boson has not been explored with the proton-proton collision data. In this paper, we reinterpret the latest ATLAS $H$+$\gamma$ resonance search results within the Standard Model effective field theory (EFT) framework, using 36.1 fb${}^{-1}$ of proton-proton collision data recorded with the ATLAS detector at $\sqrt{s}=13$ TeV. Constraints on the Wilson coefficients of dimension-six EFT operators related to the Higgs boson to photon coupling are provided for the first time in the $H$+$\gamma$ final state at the LHC.

    hep-phCPC(2019)·9 citations
11. 11*

    The fate of the Littlest Higgs with T-parity under 13 TeV LHC data

    Jürgen Reuter🇩🇪 · Daniel Dercks🇩🇪 · Gudrid Moortgat-Pick🇩🇪 · So Young Shim🇰🇷

    Little Higgs models - which can most easily be thought of as a variant of composite Higgs models - explain a light Higgs boson at 125 GeV as an pseudo-Nambu-Goldstone boson of a spontaneously broken global symmetry. The mechanism of collective symmetry breaking shifts the UV scale of these models to the 10 TeV scale and higher. T-parity is introduced as a discrete symmetry to remove tree-level constraints on the electroweak precision data. Still after run 1 of LHC, electroweak precision observables gave stronger constraints than Higgs data and direct searches. We present a full recast of all available 13 TeV searches from LHC run 2 to show that now direct searches supersede electroweak precision observables. The latest exclusion limits on the LHT model will be presented, as well as an outlook on the full high-luminosity phase of LHC.

    hep-phPoS(2019)·1 citation
12. 12*

    Dimuon enhancement at 28 GeV and tentative (pseudo)scalar partner of the Z boson at 57.5 GeV

    Eef van Beveren🇵🇹 · George Rupp🇵🇹

    The CMS Collaboration at the LHC recently reported an accumulation of data around 28 GeV in the invariant-mass distribution of muon pairs in association with a b quark jet and at least a second jet. This is analysed here in the light of the possible existence of a (pseudo)scalar boson with mass of about 57.5 GeV. We find that part of the data may originate in the radiative decay of Z bosons into pairs consisting of the lighter boson and a photon, giving rise to dimuon decay products that either stem from the photon or from the (pseudo)scalar boson.

    hep-phhep-ex5 citations
13. 13*

    Generalized Pauli-Gursey transformation and Majorana neutrinos

    Kazuo Fujikawa🇯🇵

    We discuss a generalization of the Pauli-Gursey transformation, which is motivated by the Autonne-Takagi factorization, to an arbitrary $n$ number of generations of neutrinos using $U(2n)$ that defines general canonical transformations and diagonalizes symmetric complex Majorana mass matrices in special cases. The Pauli-Gursey transformation mixes particles and antiparticles and thus changes the definition of the vacuum and C. We define C, P and CP symmetries at each Pauli frame specified by a generalized Pauli-Gursey transformation. The Majorana neutrinos in the C and P violating seesaw model are then naturally defined by a suitable choice of the Pauli frame, where only Dirac-type fermions appear with well-defined C, P and CP, and thus the C symmetry for Majorana neutrinos agrees with the C symmetry for Dirac-type fermions. This fully symmetric setting corresponds to the idea of Majorana neutrinos as Bogoliubov quasi-particles. In contrast, the conventional direct construction of Majorana neutrinos in the seesaw model, where CP is well-defined but C and P are violated, encounters the mismatch of C symmetry for Majorana neutrinos and C symmetry for chiral fermions; this mismatch is recognized as the inevitable appearance of the singlet (trivial) representation of C symmetry for chiral fermions.

    hep-phhep-thPLB(2019)·10 citations
14. 14*

    $\nu$-Inflaton Dark Matter

    Antonio Torres Manso🇵🇹 · Joao G. Rosa🇵🇹

    We present a unified model where the same scalar field can drive inflation and account for the present dark matter abundance. This scenario is based on the incomplete decay of the inflaton field into right-handed neutrino pairs, which is accomplished by imposing a discrete interchange symmetry on the inflaton and on two of the right-handed neutrinos. We show that this can lead to a successful reheating of the Universe after inflation, while leaving a stable inflaton remnant at late times. This remnant may be in the form of WIMP-like inflaton particles or of an oscillating inflaton condensate, depending on whether or not the latter evaporates and reaches thermal equilibrium with the cosmic plasma. We further show that this scenario is compatible with generating light neutrino masses and mixings through the seesaw mechanism, predicting at least one massless neutrino, and also the observed baryon asymmetry via thermal leptogenesis.

    hep-phastro-ph.COgr-qchep-thJHEP(2019)·13 citations
15. 15*

    Left-handed color-sextet diquark in the Kaon system

    Chuan-Hung Chen🇹🇼 · Takaaki Nomura🇰🇷

    We investigate whether a color-sextet scalar diquark (${\mathbf{H}}_6$) coupling to the left-handed quarks contributes to the $\Delta S=2$ process. It is found that the box diagrams mediated by $W$ and ${\mathbf{H}}_6$ bosons have no contributions to $\Delta S=2$ when the limit of $m_t=0$ is used, and the flavor mixing matrices for diagonalizing quark mass matrices are introduced at the same time. When the heavy top-quark mass effects are taken into account, it is found that in addition to the $W-{\mathbf{H}}_6$ box diagrams significantly contributing to $\Delta S=2$, their effects can be as large as those from the ${\mathbf{H}}_6-{\mathbf{H}}_6$ box diagrams. Using the parameters that are constrained by the $K^0-{\bar{K}}^0$ mixing parameter $\Delta M_K$ and the Kaon indirect CP violation ${ϵ}_K$, we find that the left-handed color-sextet diquark can lead to the Kaon direct CP violation being $Re({ϵ}^{\prime }/ϵ)\sim 0.4\times 10^{-3}$. In the chosen scheme, although the diquark contribution to $K_L\to {\pi }^0\nu \bar{\nu }$ is small, the branching ratio of $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ can reach the current experimental upper bound.

    hep-phhep-exPRD(2019)·10 citations
16. 16*

    Top Quark Anomalous Couplings at the High-Luminosity Phase of the LHC

    Frédéric Déliot🇫🇷 · Miguel C. N. Fiolhais🇺🇸 · António Onofre🇵🇹

    The combination of the latest and most precise measurements of several top quark properties is presented in this paper in order to establish allowed regions on anomalous contributions to the Lorentz structure of the $Wtb$ vertex. These measurements include single top production cross sections, $W$ boson helicity fractions and forward-backward asymmetries, both at Tevatron and at the Large Hadron Collider, up to a center-of-mass energy of 13 TeV. The results obtained at 95% Confidence Level for the top quark anomalous couplings are compared with the limits extracted from a combination that includes the expected measurements at the future High-Luminosity run of the Large Hadron Collider.

    hep-phMod.Phys.Lett.A(2019)·9 citations
17. 17*

    Self-interacting dark matter with a vector mediator: kinetic mixing with U(1)${}_{(B-L{)}_3}$ gauge boson

    Ayuki Kamada🇰🇷 · Masaki Yamada🇺🇸 · Tsutomu T. Yanagida🇯🇵

    A spontaneously broken hidden U(1)${}_h$ gauge symmetry can explain both the dark matter stability and the observed relic abundance. In this framework, the light gauge boson can mediate the strong dark matter self-interaction, which addresses astrophysical observations that are hard to explain in collisionless cold dark matter. Motivated by flavoured grand unified theories, we introduce right-handed neutrinos and a flavoured $B-L$ gauge symmetry for the third family U(1)${}_{(B-L{)}_3}$. The unwanted relic of the U(1)${}_h$ gauge boson decays into neutrinos via the kinetic mixing with the U(1)${}_{(B-L{)}_3}$ gauge boson. Indirect detection bounds on dark matter are systematically weakened, since dark matter annihilation results in neutrinos. However, the kinetic mixing between U(1)${}_{(B-L{)}_3}$ and U(1)${}_Y$ gauge bosons are induced by quantum corrections and leads to an observable signal in direct and indirect detection experiments of dark matter. This model can also explain the baryon asymmetry of the Universe via the thermal leptogenesis. In addition, we discuss the possibility of explaining the lepton flavour universality violation in semi-leptonic $B$ meson decays that is recently found in the LHCb experiment.

    hep-phastro-ph.COJHEP(2019)·33 citations
18. 18*

    Measurement of the Triple Higgs Coupling at a HE-LHC

    Samuel Homiller🇺🇸 · Patrick Meade🇺🇸

    The currently unmeasured triple Higgs coupling is one of the strong motivations for future physics programs at the LHC and beyond. A sufficiently precise measurement can lead to qualitative changes in our understanding of electroweak symmetry breaking and the cosmological history of the Higgs potential. As such, the quantitative measurement of this coupling is now one of the benchmark measurements for any proposed collider. We study the capability of a potential $27\mathrm{TeV}$ HE-LHC upgrade in measuring the Higgs trilinear coupling via the di-Higgs production process in the $b\bar{b}\gamma \gamma$ channel. We emphasize that a key background from single Higgs production via gluon fusion has been underestimated and underappreciated in prior studies. We perform a detailed study taking into account two different potential detector scenarios, and validate against HL-LHC projections from ATLAS. We find that the di-Higgs production process can be observed at $\ge 4.5\sigma$, corresponding to a $\sim 40\%$ measurement of the Higgs self-coupling, with $15{\mathrm{ab}}^{-1}$ of data at the HE-LHC.

    hep-phJHEP(2019)·31 citations
19. 19*

    Coloured coannihilations: Dark matter phenomenology meets non-relativistic EFTs

    S. Biondini🇳🇱 · S. Vogl🇩🇪

    We investigate the phenomenology of a simplified model with a Majorana fermion as dark matter candidate which interacts with Standard Model quarks via a colour-charged coannihilation partner. Recently it has been realized that non-perturbative dynamics, including the Sommerfeld effect, bound state formation/dissociation and thermal corrections, play an important role in coannihilations with coloured mediators. This calls for a careful analysis of thermal freeze-out and a new look at the experimental signatures expected for a thermal relic. We employ a state of the art calculation of the relic density which makes use of a non-relativistic effective theory framework and calculate the effective annihilation rates by solving a plasma-modified Schrodinger equation. We determine the cosmologically preferred parameter space and confront it with current experimental limits and future prospects for dark matter detection.

    hep-phJHEP(2019)·51 citations
20. 20*

    Gauge covariant approach to the electroweak interactions of mesons in the Nambu-Jona-Lasinio model with spin-1 states

    A.A. Osipov🇷🇺 · B. Hiller🇵🇹 · P.M. Zhang🇨🇳

    An extended Nambu-Jona-Lasinio (NJL) model with chiral group $U(2)\times U(2)$ and spin-0 and spin-1 four quark interactions is used to develop the gauge covariant approach to the diagonalization of the $\pi -a_1$ mixing in the presence of electroweak forces. This allows for manifestly gauge covariant description of both the non-anomalous and anomalous parts of the effective Lagrangian. It is shown that in the non-anomalous sector the theory is equivalent to the standard non-covariant approach.

    hep-phMod.Phys.Lett.A(2019)·4 citations
21. 21*

    What does Inflation say about Dark Energy given the Swampland Conjectures?

    Chien-I Chiang🇺🇸 · Jacob M. Leedom🇺🇸 · Hitoshi Murayama🇺🇸

    We discuss the relations between swampland conjectures and observational constraints on both inflation and dark energy. Using the requirement $|\nabla V|\ge cV$, with $c$ as a universal constant whose value can be derived from inflation, there may be no observable distinction between constant and non-constant models of dark energy. However, the latest modification of the above conjecture, which utilizes the second derivative of the potential, opens up the opportunity for observations to determine if the dark energy equation of state deviates from that of a cosmological constant. We also comment on the observability of tensor fluctuations despite the conjecture that field excursions are smaller than the Planck scale.

    ↳ hep-thastro-ph.COhep-phPRD(2019)·45 citations
22. 22*

    Time-varying neutrino mass from a supercooled phase transition: current cosmological constraints and impact on the ${\Omega }_m$-${\sigma }_8$ plane

    Christiane S. Lorenz🇬🇧 · Lena Funcke🇨🇦 · Erminia Calabrese🇬🇧 · Steen Hannestad🇩🇰

    In this paper we investigate a time-varying neutrino mass model, motivated by the mild tension between cosmic microwave background (CMB) measurements of the matter fluctuations and those obtained from low-redshift data. We modify the minimal case of the model proposed by Dvali and Funcke (2016) that predicts late neutrino mass generation in a post-recombination cosmic phase transition, by assuming that neutrino asymmetries allow for the presence of relic neutrinos in the late-time Universe. We show that, if the transition is supercooled, current cosmological data (including CMB temperature, polarization and lensing, baryon acoustic oscillations, and Type Ia supernovae) prefer the scale factor $a_s$ of the phase transition to be very large, peaking at $a_s\sim 1$, and therefore supporting a cosmological scenario in which neutrinos are almost massless until very recent times. We find that in this scenario the cosmological bound on the total sum of the neutrino masses today is significantly weakened compared to the standard case of constant-mass neutrinos, with $\sum m_{\nu }<4.8$~eV at 95\% confidence, and in agreement with the model predictions. The main reason for this weaker bound is a large correlation arising between the dark energy and neutrino components in the presence of false vacuum energy that converts into the non-zero neutrino masses after the transition. This result provides new targets for the coming KATRIN and PTOLEMY experiments. We also show that the time-varying neutrino mass model considered here does not provide a clear explanation to the existing cosmological ${\Omega }_m$-${\sigma }_8$ discrepancies.

    ↳ astro-ph.COhep-phPRD(2019)·64 citations
23. 23*

    New Inflation in the Landscape and Typicality of the Observed Cosmic Perturbation

    Chien-I Chiang🇺🇸 · Keisuke Harigaya🇺🇸

    We investigate if the observed small and nearly scale-invariant primordial cosmic perturbation, i.e. the perturbation amplitude $P_{\zeta }\sim 10^{-9}$ and the spectral index $n_s\simeq 0.965$, is typical in the landscape of vacua after imposing anthropic selections on them. We consider the situation where the universe begins from a metastable vacuum driving a precedent inflation, a curvature-dominated open universe is created by tunneling, and the curvature energy is inflated away by new inflation. We argue that the initial inflaton field value is homogeneous but typically non-zero because of the quantum fluctuation of long wavelength modes created during the precedent inflation, and only the universe which accidentally has a small inflaton field value is anthropically selected. We show that this bias, together with certain distributions of inflation model parameters that are physically well-motivated, makes the observed small and nearly scale-invariant spectrum typical.

    ↳ astro-ph.COhep-phhep-thPRD(2019)·5 citations
24. 24*

    HIJING++, a Heavy Ion Jet INteraction Generator for the High-luminosity Era of the LHC and Beyond

    Gábor Bíró🇭🇺 · Gábor Papp🇭🇺 · Gergely Gábor Barnaföldi🇭🇺 · Dániel Nagy🇭🇺 · Miklos Gyulassy🇭🇺 · Péter Lévai🇭🇺 · Xin-Nian Wang🇨🇳 · Ben-Wei Zhang🇨🇳

    HIJING++ (Heavy Ion Jet INteraction Generator) is the successor of the widely used original HIJING, developed almost three decades ago. While the old versions (1.x and 2.x) were written in FORTRAN, HIJING++ was completely rewritten in C++. During the development we keep in mind the requirements of the high-energy heavy-ion community: the new Monte Carlo software have a well designed modular framework, therefore any future modifications are much easier to implement. It contains all the physical models that were also present in it's predecessor, but utilizing modern C++ features it also includes native thread based parallelism, an easy-to-use analysis interface and a modular plugin system, which makes room for possible future improvements. In this paper we summarize the results of our performance tests measured on 2 widely used architectures.

    ↳ physics.comp-phhep-phMDPI Proc.(2019)·9 citations
25. 25*

    Nucleon-$J/\psi$ and nucleon-${\eta }_c$ scattering in $P_c$ pentaquark channels from LQCD

    Ursa Skerbis🇸🇮 · Sasa Prelovsek🇸🇮

    The lattice QCD simulation of $NJ/\psi$ and $N{\eta }_c$ scattering is performed at $m_{\pi }\simeq 266$MeV in channels with all possible $J^P$. This includes $J^P=3/2^{\pm }$ and $5/2^{\pm }$ where LHCb discovered $P_c(4380)$ and $P_c(4450)$ pentaquark states in proton$-J/\psi$ decay. This is the first lattice simulation that reaches the energies 4.3-4.5 GeV where pentaquarks reside. Several decay channels are open in this energy region and we explore the fate of $P_c$ in the one-channel approximation in this work. Energies of eigenstates are extracted for the nucleon-charmonium system at zero total momentum for all quantum numbers, i.e. six lattice irreducible representations. No significant energy shifts are observed. The number of the observed lattice eigenstates agrees with the number expected for non-interacting charmonium and nucleon. Thus, we do not find any strong indication for a resonance or a bound state in these exotic channels within one-channel approximation. This possibly indicates that the coupling of $NJ/\psi$ channel with other two-hadron channels might be responsible for $P_c$ resonances in experiment. One of the challenges of this study is that up to six degenerate $J/\psi (p)N(-p)$ eigenstates are expected in the non-interacting limit due non-zero spins of $J/\psi$ and N, and we establish all of them in the spectra.

    ↳ hep-lathep-phPRD(2019)·59 citations
26. 26*

    Unraveling the effective fluid approach for $f(R)$ models in the subhorizon approximation

    Rubén Arjona🇪🇸 · Wilmar Cardona🇪🇸 · Savvas Nesseris🇪🇸

    We provide explicit formulas for the effective fluid approach of $f(R)$ theories, such as the Hu & Sawicki and the designer models. Using the latter and simple modifications to the CLASS code, which we call EFCLASS, in conjunction with very accurate analytic approximations for the background evolution, we obtain competitive results in a much simpler and less error-prone approach. We also derive the initial conditions in matter domination and we find they differ from those already found in the literature for a constant $w$ model. A clear example is the designer model that behaves as $\Lambda$CDM in the background, but has nonetheless dark energy perturbations. We then use the aforementioned models to derive constraints from the latest cosmological data, including supernovae, BAO, CMB, $H(z)$ and growth-rate data, and find they are statistically consistent to the $\Lambda$CDM model. Finally, we show that the viscosity parameter $c_{vis}^2$ in realistic models is not constant as commonly assumed, but rather evolves significantly over several orders of magnitude, something which could affect forecasts of upcoming surveys.

    ↳ astro-ph.COgr-qchep-phPRD(2019)·95 citations
27. 27*

    QCD phase diagram for finite imaginary chemical potential with HISQ fermions

    Jishnu Goswami🇩🇪 · Frithjof Karsch🇩🇪 · Anirban Lahiri🇩🇪 · Christian Schmidt🇩🇪

    We present results from an ongoing study of the phase diagram of (2+1)-flavor QCD using the HISQ action with smaller than physical light quark masses in the Roberge-Weiss (RW) plane on lattices with temporal extent $N_{\tau }=4$. We find that the endpoint of the $1^{st}$ order RW transition line remains $2^{nd}$ order at least down to light quark masses corresponding to Goldstone pion masses of $55$ MeV. Furthermore, we show that the chiral condensate is sensitive to the RW transition and may serve as a energy-like operator characterizing universal behavior close to the RW endpoint.

    ↳ hep-lathep-phnucl-thPoS(2018)·11 citations
28. 28*

    Amplitudes from anomalous superconformal symmetry

    Dmitry Chicherin🇩🇪 · Johannes M. Henn🇩🇪 · Emery Sokatchev🇫🇷

    We initiate a systematic study of the consequences of (super)conformal symmetry of massless scattering amplitudes. The classical symmetry is potentially broken at the quantum level by infrared and ultraviolet effects. We study its manifestations on the finite hard part of the scattering process. The conformal Ward identities in momentum space are second-order differential equations, difficult to analyze. We prefer to study superconformal symmetry whose generators are first-order in the momenta. Working in a massless N=1 supersymmetric Wess-Zumino model, we derive on-shell superconformal Ward identities. They contain an anomaly due to collinear regions of loop momenta. It is given by an integral with one loop less than the original graph, with an extra integral over a collinear splitting parameter. We discuss the relation to the holomorphic anomaly that was previously studied in tree-level amplitudes and at the level of unitarity cuts. We derive and solve Ward identities for various scattering processes in the model. We classify the on-shell superamplitudes according to their Grassmann degree, in close analogy with the helicity classification of gluon amplitudes. We focus on MHV-like and NMHV-like amplitudes with up to six external particles, at one and two loops. Interestingly, the superconformal generator acting on the bosonic part of the amplitudes is Witten's twistor collinearity operator. We find that the first-order differential equations, together with physically motivated boundary conditions, uniquely fix the answer. All the cases considered give rise to uniform weight functions. Our most interesting example is a five-point non-planar hexa-box integral with an off-shell leg. It gives first indications on the function space needed for Higgs plus two jet production at next-to-next-to leading order.

    ↳ hep-thhep-phJHEP(2019)·8 citations
29. 29*

    Spectator Dark Matter

    Tommi Markkanen🇬🇧 · Arttu Rajantie🇬🇧 · Tommi Tenkanen🇬🇧

    The observed dark matter abundance in the Universe can be fully accounted for by a minimally coupled spectator scalar field that was light during inflation and has sufficiently strong self-coupling. In this scenario, dark matter was produced during inflation by amplification of quantum fluctuations of the spectator field. The self-interaction of the field suppresses its fluctuations on large scales, and therefore avoids isocurvature constraints. The scenario does not require any fine-tuning of parameters. In the simplest case of a single real scalar field, the mass of the dark matter particle would be in the range $1\mathrm{GeV}\lesssim m\lesssim 10^8\mathrm{GeV}$, depending on the scale of inflation, and the lower bound for the quartic self-coupling is $\lambda \gtrsim 0.45$.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2018)·79 citations
30. 30*

    Generalized Conformal Transformation and Inflationary Attractors

    Khamphee Karwan (Naresuan U.)🇹🇭 · Phongpichit Channuie (Walailak U.)🇹🇭

    We investigate the inflationary attractors in models of inflation inspired from general conformal transformation of general scalar-tensor theories to the Einstein frame. The coefficient of the conformal transformation in our study depends on both the scalar field and its kinetic term. Therefore the relevant scalar-tensor theories display the subset of the class I of the degenerate higher-order scalar-tensor theories in which both the scalar field and its kinetic term can non-minimally couple to gravity. We find that if the conformal coefficient $\Omega$ takes a multiplicative form such that $\Omega \equiv w(\varphi )W(X)$ where $X$ is the kinetic term of the field $\varphi$, the theoretical predictions of the proposed model can have usual universal attractor independent of any functions of $W(X)$. For the case where $\Omega$ takes an additive form, such that $\Omega \equiv w(\varphi )+k(\varphi )\Xi (X)$, we find that there are new $\xi$ attractors in addition to the universal ones. We analyze the inflationary observables of these models and compare them to the latest constraints from the Planck collaboration. We find that the observable quantities associated to these new $\xi$ attractors do not satisfy the constraints from Planck data at a strong coupling limit.

    ↳ gr-qchep-phhep-thPRD(2019)·4 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.