Wed·Jan 31, 2018Wednesday·January 31, 2018

1. 01*

   Vacuum-like jet fragmentation in a dense QCD medium

   P. Caucal🇫🇷 · E. Iancu🇫🇷 · A.H. Mueller🇺🇸 · G. Soyez🇫🇷

   We study the fragmentation of a jet propagating in a dense quark-gluon plasma. Using a leading, double-logarithmic approximation in perturbative QCD, we compute for the first time the effects of the medium on the vacuum-like emissions. We show that, due to the scatterings off the plasma, the in-medium parton showers differ from the vacuum ones in two crucial aspects: their phase-space is reduced and the first emission outside the medium can violate angular ordering. We compute the jet fragmentation function and find results in qualitative agreement with measurements at the LHC.

   hep-phnucl-thPRL(2018)·160 citations
2. 02*

   What does the matter created in high multiplicity proton-nucleus collisions teach us about the 3-D structure of the proton?

   K. Dusling🇺🇸 · M. Mace🇺🇸 · R. Venugopalan🇺🇸

   The study of multiparticle correlations and collectivity in the hot and dense matter created in collisions of heavy-ions as well as those of smaller systems such as proton--heavy-ion collisions has progressed to the point where detailed knowledge of the three-dimensional structure of the proton is needed to confront experimental data. We discuss results from a simple proof-of-principle initial state parton model which reproduces many features of the data on proton--heavy-ion collisions that are often ascribed to hydrodynamic flow. We outline how this model can be further improved with particular emphasis on missing elements in our understanding of the dynamical spatial and momentum structure of the proton.

   hep-phnucl-exnucl-thPoS(2018)·7 citations
3. 03*

   Pileup mitigation at the LHC: a theorist's view

   Gregory Soyez🇫🇷

   To maximise the potential for new measurements and discoveries at the LHC, the machine delivers as high as possible collision rates. As a consequence, multiple proton-proton collisions occur whenever two bunches cross. Interesting high-energy (hard) collisions are therefore contaminated by several soft, zero-bias, ones. This effect known as pileup pollutes the final state of the collision. It complicates the reconstruction of the objects in this final state, resulting in increased experimental uncertainties. To reduce these uncertainties, and improve the quality and precision of LHC measurements, techniques are devised to correct for the effects of pileup. This document provides a theoretical review of the main methods used during Run I and II of the LHC to mitigate pileup effects. I start with an in-depth presentation of the area--median used for the majority of applications, including several refinements of the original idea, their practical implementation and an assessment of their efficiency and robustness. I then focus on several theoretical calculations that can provide both quantitative and qualitative information on the area--median approach. In the case of boosted jets, a field that has seen a wide interest recently, a set of methods, known as grooming techniques has also been used. I describe these techniques, address their performance and briefly show that they are amenable to a theoretical, analytic, understanding. The last part of this review focuses on ideas oriented towards future pileup mitigation techniques. This includes new methods that have recently been proposed as well as a large series of alternative ideas. The latter are yet unpublished and have not received the same amount of investigation than the former but they have the potential to bring new developments and further improvement over existing techniques in a future where pileup mitigation will be crucial.

   hep-phhep-exPhys.Rept.(2019)·73 citations
4. 04*

   Status of Flavour Maximal Non-minimal Universal Extra Dimension

   Sayan Dasgupta🇮🇳 · Ujjal Kumar Dey🇮🇳 · Tapoja Jha🇮🇳 · Tirtha Sankar Ray🇮🇳

   In this paper we consider an $S^1/{\mathbb{Z}}_2$ compactified flat extra dimensional scenario where all the standard model states can access the bulk and have generalised brane localised kinetic terms. The flavour structure of brane kinetic terms for the standard model fermions are dictated by stringent flavour bounds on the first two generations implying an $U(2{)}_{Q_L}\otimes U(2{)}_{u_R}\otimes U(2{)}_{d_R}$ flavour symmetry. We consider the constraints on such a scenario arising from dark matter relic density and direct detection measurements, precision electroweak data, Higgs physics and LHC dilepton searches. We discuss the possibility of such a scenario providing an explanation of the recently measured anomaly in $R_{K^{(\ast )}}$ within the allowed region of the parameter space.

   hep-phPRD(2018)·18 citations
5. 05*

   Anomaly mediated SUSY breaking model retrofitted for naturalness

   Howard Baer🇺🇸 · Vernon Barger🇺🇸 · Dibyashree Sengupta🇺🇸

   Anomaly-mediated supersymmetry breaking (AMSB) models seem to have become increasingly implausible due to 1. difficulty in generating a Higgs mass m(h)~125 GeV, 2. typically unnatural superparticle spectra characterized by a large superpotential mu term and 3. the possibility of a wino-like lightest SUSY particle (LSP) as dark matter now seems to be excluded. In the present paper we propose some minor modifications to the paradigm model which solve these three issues. Instead of adding a universal bulk scalar mass to avoid tachyonic sleptons, we add distinct Higgs and matter scalar soft masses which then allow for light higgsinos. To gain accord with the measured Higgs mass, we also include a bulk trilinear soft term. The ensuing natural generalized AMSB (nAMSB) model then has a set of light higgsinos with mass nearby the weak scale m(W,Z,h)~100 GeV as required by naturalness while the winos populate the several hundred GeV range and gluinos and squarks occupy the multi-TeV range. For LHC searches, the wino pair production followed by decay to same-sign diboson signature channel offers excellent prospects for discovery at high luminosity LHC along with higgsino pair production leading to soft dileptons plus jet(s)+MET. A linear e^+e^- collider operating above higgsino pair production threshold should be able to distinguish the AMSB gaugino spectra from unified or mirage unified scenarios. Dark matter is expected to occur as a higgsino-like WIMP plus axion admixture.

   hep-phPRD(2018)·36 citations
6. 06*

   Neutrino conversion in a neutrino flux: Towards an effective theory of collective oscillations

   Rasmus S. L. Hansen🇩🇪 · Alexei Yu. Smirnov🇩🇪

   Collective oscillations of supernova neutrinos above the neutrino sphere can be completely described by the propagation of individual neutrinos in external potentials and are in this sense a linear phenomenon. An effective theory of collective oscillations can be developed based on certain assumptions about time dependence of these potentials. General conditions for strong flavor transformations are formulated and these transformations can be interpreted as parametric resonance effects induced by periodic modulations of the potentials. We study a simplified and solvable example, where a probe neutrino is propagating in a flux of collinear neutrinos, such that $\nu \nu -$ interactions in the flux are absent. Still, this example retains the main feature - the coherent flavor exchange. Properties of the parametric resonance are studied, and it is shown that integrations over energies and emission points of the flux neutrinos suppress modulations of the potentials and therefore strong transformations. The transformations are also suppressed by changes in densities of background neutrinos and electrons.

   hep-phastro-ph.HEJCAP(2018)·8 citations
7. 07*

   $N^{\ast }$ Production from $e^{+}{e}^{-}$ Annihilations

   Bing-Song Zou🇨🇳

   Up to now, the $N^{\ast }$ production from $e^{+}{e}^{-}$ annihilations has been studied only around charmonium region. Charmonium decays to $N^{\ast }$s are analogous to (time-like) EM form factors in that the charm quark annihilation provides a nearly pointlike (ggg) current. Complementary to other sources, such as $\pi N$, $eN$ and $\gamma N$ reactions, this new source for $N^{\ast }$ spectroscopy has a few advantages, such as an isospin filter and a low spin filter. The experimental results on $N^{\ast }$ from $e^{+}{e}^{-}$ annihilations and their phenomenological implications are reviewed. Possible new sources on $N^{\ast }$ production from $e^{+}{e}^{-}$ annihilations are discussed.

   hep-phhep-exnucl-exnucl-th5 citations
8. 08*

   Spin portal to dark matter

   H. Hernández-Arellano🇲🇽 · M. Napsuciale🇲🇽 · S. Rodríguez🇲🇽

   In this work we study the possibility that dark matter fields transform in the $(1,0)\oplus (0,1)$ representation of the Homogeneous Lorentz Group. In an effective theory approach, we study the lowest dimension interacting terms of dark matter with standard model fields, assuming that dark matter fields transform as singlets under the standard model gauge group. There are three dimension-four operators, two of them yielding a Higgs portal to dark matter. The third operator couple the photon and $Z^0$ fields to the higher multipoles of dark matter, yielding a \textit{spin portal} to dark matter. For dark matter ($D$) mass below a half of the $Z^0$ mass, the decays $Z^0\to \bar{D}D$ and $H\to \bar{D}D$ are kinematically allowed and contribute to the invisible widths of the $Z^0$ and $H$. We calculate these decays and use experimental results on these invisible widths to constrain the values of the low energy constants finding in general that effects of the spin portal can be more important that those of the Higgs portal. We calculate the dark matter relic density in our formalism, use the constraints on the low energy constants from the $Z^0$ and $H$ invisible widths and compare our results with the measured relic density, finding that dark matter with a $(1,0)\oplus (0,1)$ space-time structure must have a mass $M>43GeV$.

   hep-phhep-thPRD(2018)·12 citations
9. 09*

   Stop Coannihilation in the CMSSM and SubGUT Models

   John Ellis🇬🇧 · Jason L. Evans🇰🇷 · Feng Luo🇯🇵 · Keith A. Olive🇺🇸 · Jiaming Zheng🇯🇵

   Stop coannihilation may bring the relic density of heavy supersymmetric dark matter particles into the range allowed by cosmology. The efficiency of this process is enhanced by stop-antistop annihilations into the longitudinal (Goldstone) modes of the $W$ and $Z$ bosons, as well as by Sommerfeld enhancement of stop annihilations and the effects of bound states. Since the couplings of the stops to the Goldstone modes are proportional to the trilinear soft supersymmetry-breaking $A$-terms, these annihilations are enhanced when the $A$-terms are large. However, the Higgs mass may be reduced below the measured value if the $A$-terms are too large. Unfortunately, the interpretation of this constraint on the stop coannihilation strip is clouded by differences between the available Higgs mass calculators. For our study, we use as our default calculator FeynHiggs 2.13.0, the most recent publicly available version of this code. Exploring the CMSSM parameter space, we find that along the stop coannihilation strip the masses of the stops are severely split by the large $A$-terms. This suppresses the Higgs mass drastically for $\mu$ and $A_0>0$, whilst the extent of the stop coannihilation strip is limited for $A_0<0$ and either sign of $\mu$. However, in sub-GUT models, reduced renormalization-group running mitigates the effect of the large $A$-terms, allowing larger LSP masses to be consistent with the Higgs mass calculation. We give examples where the dark matter particle mass may reach $\gtrsim 8$ TeV.

   hep-phEPJC(2018)·38 citations
10. 10*

    Chiral Lagrangians with decuplet baryons to one loop

    Shao-Zhou Jiang🇨🇳 · Yan-Rui Liu🇨🇳 · Hong-Qian Wang🇨🇳 · Qin-He Yang🇨🇳

    We construct the relativistic chiral Lagrangians with decuplet baryons up to the order $\mathcal{O}(p^4)$ (one loop). For the meson-decuplet-decuplet couplings, there are 1, 13, 55, and 548 terms in the $\mathcal{O}(p^1)$-$\mathcal{O}(p^4)$ order Lagrangians, respectively. For the meson-octet-decuplet Lagrangians, the number of independent terms from $\mathcal{O}(p^1)$ to $\mathcal{O}(p^4)$ are 1, 5, 67, and 611, respectively. For convenience of applications, the $\pi \Delta \Delta$ and $\pi N\Delta$ chiral Lagrangians are picked out. This new form of $\Delta$ Lagrangians is equivalent to the original isovector-isospinor one and we establish relations between these two forms.

    hep-phnucl-thPRD(2018)·7 citations
11. 11*

    $\mu -\tau$ Reflection Symmetry Embedded in Minimal Seesaw

    Newton Nath🇨🇳 · Zhi-zhong Xing🇨🇳 · Jue Zhang🇨🇳

    We embed $\mu -\tau$ reflection symmetry into the minimal seesaw formalism, where two right-handed neutrinos are added to the Standard Model of particle physics. Assuming that both the left- and right-handed neutrino fields transform under $\mu -\tau$ reflection symmetry, we obtain the required forms of the neutrino Dirac mass matrix and the Majorana mass matrix for the right-handed neutrinos. To investigate the neutrino phenomenology at low energies, we first consider the breaking of $\mu -\tau$ reflection symmetry due to the renormalization group running, and then systematically study various breaking schemes by introducing explicit breaking terms at high energies.

    hep-phEPJC(2018)·48 citations
12. 12*

    Assisted Vacuum Decay by Time Dependent Electric Fields

    Andreas Otto🇩🇪 · Hans Oppitz🇩🇪 · Burkhard Kämpfer🇩🇪

    We consider the vacuum decay by electron-positron pair production in spatially homogeneous, time dependent electric fields by means of quantum kinetic equations. Our focus is on the impact of various pulse shapes as envelopes of oscillating fields and the assistance effects in multi-scale fields, which are also seen in photons accompanying the creation and motion of pairs.

    hep-phEPJA(2018)·16 citations
13. 13*

    Digluon contribution to $J/\psi$ production

    Ivan Schmidt🇨🇱 · Marat Siddikov🇨🇱

    In this paper we study the contribution of the double parton distributions of gluons to the charmonium production. Despite being suppressed in the heavy quark mass limit, numerically this contribution gives a sizeable correction to the leading order $k_T$ factorization result in LHC kinematics due to enhancement of gluonic densities in the small Bjorken $x_B$ limit. This contribution is not suppressed at large $J/\psi$ momenta $p_T$ and thus presents one of the complementary mechanisms of charmonia production in this kinematics.

    hep-phJ.Phys.G(2019)·6 citations
14. 14*

    Simplest Little Higgs Revisited: Hidden Mass Relation, Unitarity and Naturalness

    Kingman Cheung🇹🇼 · Shi-Ping He🇨🇳 · Ying-nan Mao🇨🇳 · Chen Zhang🇹🇼 · Yang Zhou🇨🇳

    We analyze the scalar potential of the Simplest Little Higgs (SLH) model in an approach consistent with the spirit of continuum effective field theory (CEFT). By requiring correct electroweak symmetry breaking (EWSB) with the $125\text{GeV}$ Higgs boson, we are able to derive a relation between the pseudo-axion mass $m_{\eta }$ and the heavy top mass $m_T$, which serves as a crucial test of the SLH mechanism. By requiring $m_{\eta }^2>0$ an upper bound on $m_T$ can be obtained for any fixed SLH global symmetry breaking scale $f$. We also point out that an absolute upper bound on $f$ can be obtained by imposing partial wave unitarity constraint, which in turn leads to absolute upper bounds of $m_T\lesssim 19\text{TeV},m_{\eta }\lesssim 1.5\text{TeV}$ and $m_{Z^{\prime }}\lesssim 48\text{TeV}$. We present the allowed region in the three-dimensional parameter space characterized by $f,t_{\beta },m_T$, taking into account the requirement of valid EWSB and the constraint from perturbative unitarity. We also propose a strategy of analyzing the fine-tuning problem consistent with the spirit of CEFT and apply it to the SLH. We suggest that the scalar potential and fine-tuning analysis strategies adopted here should also be applicable to a wide class of Little Higgs and Twin Higgs models, which may reveal interesting relations as crucial tests of the related EWSB mechanism and provide a new perspective on assessing their degree of fine-tuning.

    hep-phPRD(2018)·5 citations
15. 15*

    The Dynamics of Beauty & Charm Hadrons and top quarks in the Era of the LHCb & Belle II and ATLAS/CMS, Motto: Non-perturbative QCD \& Many-body Final States

    I.I. Bigi🇺🇸

    Our community has to apply {\em non}-perturbative QCD on different levels of flavor dynamics in strange, charm \& beauty hadrons and even for top quarks. We need {\em consistent} parameterization of the CKM matrix and describe weak decays of beauty hadrons with {\em many-body} final states. It is crucial to use the {\em Wilsonian} OPE as much as possible and discuss "duality" in the worlds of quarks and hadrons. The pole mass of heavy quarks is {\em not} well-defined on the {\em non}-perturbative level -- i.e., it is {\em not} Borel summable in total QCD. We need a novel team to combine the strengths of our tools from MEP and HEP.

    hep-phActa Phys.Polon.B(2018)·0 citations
16. 16*

    Relating CP-violating decays to the neutron EDM

    Thomas Gutsche🇩🇪 · Astrid N. Hiller Blin🇩🇪 · Sergey Kovalenko🇨🇱 · Serguei Kuleshov🇨🇱 · Valery E. Lyubovitskij🇩🇪 · Manuel J. Vicente Vacas🇪🇸 · Alexey Zhevlakov🇷🇺

    We use the present upper bound on the neutron electric dipole moment to give an estimate for the upper limit of the CP-violating couplings of the $\eta ({\eta }^{\prime })$ meson to the neutron. Using this result, we derive constraints on the CP-violating two-pion decays of the $\eta ({\eta }^{\prime })$. Our results are relevant for the running and planned GlueX and LHCb measurements of rare meson decays.

    hep-phFew Body Syst.(2018)·2 citations
17. 17*

    Neutrino masses in a conformal multi-Higgs-doublet model

    Manuel Fink🇦🇹 · Helmut Neufeld🇦🇹

    We construct a conformal version of a general multi-Higgs-doublet model with additional right-handed neutrino gauge-singlets. Assuming a minimal extension of the scalar sector by a real singlet field, we show that the resulting model achieves the same attractive properties as the non-conformal theory, combining the seesaw mechanism and higher-order mass production to generate naturally light neutrino masses. Starting with dimensionless couplings only, all masses and energy scales in the theory (including the heavy Majorana masses and the electroweak scale) are obtained from dimensional transmutation via the Coleman-Weinberg mechanism. A characteristic feature of the conformal model is the appearance of the scalon in the scalar spectrum.The mass of this particle, which can be expressed in terms of the masses of the other particles in the theory, is produced at the one-loop level. We establish a connection between the large seesaw scale and a suppression of the scalon interactions. The positivity condition for the squared scalon mass requires sufficiently large masses of the additional Higgs bosons balancing the contributions of the heavy neutrinos.

    hep-ph5 citations
18. 18*

    Inclusive $h_c$ production and energy spectrum from $e^{+}{e}^{-}$ annihilation at Super $B$ factory

    Qing-Feng Sun🇨🇳 · Yu Jia🇨🇳 · Xiaohui Liu🇨🇳 · Ruilin Zhu🇨🇳

    We calculate the next-to-leading order (NLO) radiative correction to the color-octet $h_c$ inclusive production in $e^{+}{e}^{-}$ annihilation at Super $B$ factory, within the nonrelativistic QCD factorization framework. The analytic expression for the NLO short-distance coefficient (SDC) accompanying the color-octet production operator ${\mathcal{O}}_8^{h_c}{(}^1{S}_0)$ is obtained after summing both virtual and real corrections. The size of NLO correction for the color-octet production channel is found to be positive and substantial. The NLO prediction to the $h_c$ energy spectrum is plagued with unphysical endpoint singularity. With the aid of the soft-collinear effective theory, those large endpoint logarithms are resummed to the next-to-leading logarithmic (NLL) accuracy. Consequently, further supplemented with the non-perturbative shape function, we obtain the well-behaved predictions for the $h_c$ energy spectrum in the entire kinematic range, which awaits the examination by the forthcoming Belle II experiment.

    hep-phhep-exPRD(2018)·8 citations
19. 19*

    Precise test of Higgs properties via triple Higgs production in VBF at future colliders

    A. S. Belyaev🇬🇧 · P. B. Schaefers🇬🇧 · M. C. Thomas🇬🇧

    For certain classes of Beyond the Standard Model theories, including composite Higgs models, the coupling of the Higgs to gauge bosons can be different from the Standard Model one. In this case, the multi-boson production via vector boson fusion (VBF) can be hugely enhanced in comparison to the SM production one due to the lack of cancellation in longitudinal vector boson scattering. Among these processes, triple Higgs boson production in VBF plays a special role - its enhancement is especially spectacular due to the absence of background from transversely polarised vector bosons in the final state. While the rates from $pp\to jjhhh$ production in vector boson fusion are too low at the LHC and even at future 33 TeV $pp$ colliders, we have found that the 100 TeV $pp$ future circular collider (FCC) has the unique opportunity to probe the $hVV$ coupling far beyond the LHC sensitivity. We have evaluated the $pp\to jjhhh$ rates as a function of deviation from the $hVV$ coupling and have found that the background is much smaller than the signal for observable signal rates. We also found that the 100 TeV $pp$ FCC can probe the $hVV$ coupling up to the permille level, which is far beyond the LHC reach. These results highlight a special role of the $hhh$ VBF production and stress once more the importance of the 100 TeV $pp$ FCC.

    hep-phPRD(2019)·13 citations
20. 20*

    Learning to Classify from Impure Samples with High-Dimensional Data

    Patrick T. Komiske🇺🇸 · Eric M. Metodiev🇺🇸 · Benjamin Nachman🇺🇸 · Matthew D. Schwartz🇺🇸

    A persistent challenge in practical classification tasks is that labeled training sets are not always available. In particle physics, this challenge is surmounted by the use of simulations. These simulations accurately reproduce most features of data, but cannot be trusted to capture all of the complex correlations exploitable by modern machine learning methods. Recent work in weakly supervised learning has shown that simple, low-dimensional classifiers can be trained using only the impure mixtures present in data. Here, we demonstrate that complex, high-dimensional classifiers can also be trained on impure mixtures using weak supervision techniques, with performance comparable to what could be achieved with pure samples. Using weak supervision will therefore allow us to avoid relying exclusively on simulations for high-dimensional classification. This work opens the door to a new regime whereby complex models are trained directly on data, providing direct access to probe the underlying physics.

    hep-phhep-exstat.MLPRD(2018)·87 citations
21. 21*

    Solar Neutrinos as a Signal and Background in Direct-Detection Experiments Searching for Sub-GeV Dark Matter With Electron Recoils

    Rouven Essig🇺🇸 · Mukul Sholapurkar🇺🇸 · Tien-Tien Yu🇺🇸

    Direct-detection experiments sensitive to low-energy electron recoils from sub-GeV dark matter (DM) interactions will also be sensitive to solar neutrinos via coherent neutrino-nucleus scattering (CNS), since the recoiling nucleus can produce a small ionization signal. Solar neutrinos constitute both an interesting signal in their own right and a potential background to a DM search that cannot be controlled or reduced by improved shielding, material purification and handling, or improved detector design. We explore these two possibilities in detail for semiconductor (Si and Ge) and Xe targets, considering several possibilities for the unmeasured ionization efficiency at low energies. For DM-electron-scattering searches, neutrinos start being an important background for exposures larger than ~1-10 kg-years in Si and Ge, and for exposures larger than ~0.1-1 kg-year in Xe. For the absorption of bosonic DM (dark photons and axion-like particles) by electrons, neutrinos are most relevant for masses below ~1 keV and again slightly more important in Xe. Treating the neutrinos as a signal, we find that the CNS of B-8 neutrinos can be observed with ~2 sigma significance with exposures of ~2, 7, and 20 kg-years in Xe, Ge, and Si, respectively, assuming there are no other backgrounds. We give an example for how this would constrain non-standard neutrino interactions. Neutrino components at lower energy can only be detected if the ionization efficiency is sufficiently large. In this case, observing pep neutrinos via CNS requires exposures ~10-100 kg-years in Si or Ge (~1000 kg-years in Xe), and observing CNO neutrinos would require an order of magnitude more exposure. Only Si could potentially detect Be-7 neutrinos. These measurements would allow for a direct measurement of the electron-neutrino survival probability over a wide energy range.

    hep-phastro-ph.COPRD(2018)·112 citations
22. 22*

    Cosmologically Viable Low-energy Supersymmetry Breaking

    Anson Hook (1)🇺🇸 · Robert McGehee (2 and 3)🇺🇸 · Hitoshi Murayama (2,3,4) ((1) Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, (2) Department of Physics, University of California, Berkeley, (3) Theoretical Physics Group, Lawrence Berkeley National Laboratory, (4) Kavli Institute for the Physics and Mathematics of the Universe (WPI))🇺🇸

    A recent cosmological bound on the gravitino mass, $m_{3/2}<4.7$ eV, together with LHC results on the Higgs mass and direct searches, excludes minimal gauge mediation with high reheating temperatures. We discuss a minimal, vector-mediated model which incorporates the seesaw mechanism for neutrino masses, allows for thermal leptogenesis, ameliorates the $\mu$ problem, and achieves the observed Higgs mass and a gravitino as light as $1$-$2$ eV.

    hep-phPRD(2018)·22 citations
23. 23*

    Searching for Dark Photon Dark Matter with Gravitational Wave Detectors

    Aaron Pierce🇺🇸 · Keith Riles🇺🇸 · Yue Zhao🇺🇸

    If dark matter stems from the background of a very light gauge boson, this gauge boson could exert forces on test masses in gravitational wave detectors, resulting in displacements with a characteristic frequency set by the gauge boson mass. We outline a novel search strategy to hunt for such dark matter, and show that both ground-based and future space-based gravitational wave detectors have the capability to make a 5$\sigma$ discovery in unexplored parameter regimes.

    hep-phastro-ph.HEgr-qcPRL(2018)·175 citations
24. 24*

    Probability Density Functions for CP-Violating Rephasing Invariants

    Jean-François Fortin🇨🇦 · Nicolas Giasson🇨🇦 · Luc Marleau🇨🇦

    The implications of the anarchy principle on CP violation in the lepton sector are investigated. A systematic method is introduced to compute the probability density functions for the CP-violating rephasing invariants of the PMNS matrix from the Haar measure relevant to the anarchy principle. Contrary to the CKM matrix which is hierarchical, it is shown that the Haar measure, and hence the anarchy principle, are very likely to lead to the observed PMNS matrix. Predictions on the CP-violating Dirac rephasing invariant $|j_D|$ and Majorana rephasing invariant $|j_1|$ are also obtained. They correspond to $⟨|j_D|{⟩}_{\text{Haar}}=\pi /105\approx 0.030$ and $⟨|j_1|{⟩}_{\text{Haar}}=1/(6\pi )\approx 0.053$ respectively, in agreement with the experimental hint from T2K of $|j_D^{\text{exp}}|\approx 0.032\pm 0.005$ (or $\approx 0.033\pm 0.003$) for the normal (or inverted) hierarchy.

    hep-phNPB(2018)·5 citations
25. 25*

    Anisotropic hydrodynamics with a scalar collisional kernel

    Dekrayat Almaalol🇺🇸 · Michael Strickland🇺🇸

    Prior studies of non-equilibrium dynamics using anisotropic hydrodynamics have used the relativistic Anderson-Witting scattering kernel or some variant thereof. In this paper, we make the first study of the impact of using a more realistic scattering kernel. For this purpose, we consider a conformal system undergoing transversally-homogenous and boost-invariant Bjorken expansion and take the collisional kernel to be given by the leading order 2 <-> 2 scattering kernel in scalar lambda phi^4. We consider both classical and quantum statistics in order to assess the impact of Bose enhancement on the dynamics. We also determine the anisotropic non-equilibrium attractor of a system subject to this collisional kernel. We find that, when the near-equilibrium relaxation-times in the Anderson-Witting and scalar collisional kernels are matched, the scalar kernel results in a higher degree of momentum-space anisotropy during the system's evolution, given the same initial conditions. Additionally, we find that taking into account Bose enhancement further increases the dynamically generated momentum-space anisotropy.

    hep-phnucl-thPRC(2018)·34 citations
26. 26*

    ${\eta }_c$ production in photon - induced interactions at the LHC

    V. P. Goncalves🇧🇷 · B. D. Moreira🇧🇷

    In this paper we investigate the ${\eta }_c$ production by photon - photon and photon - hadron interactions in $pp$ and $pA$ collisions at the LHC energies. The inclusive and diffractive contributions for the ${\eta }_c$ photoproduction are estimated using the nonrelativistic quantum chromodynamics (NRQCD) formalism. We estimate the rapidity and transverse momentum distributions for the ${\eta }_c$ photoproduction in hadronic collisions at the LHC and present our estimate for the total cross sections at the Run 2 energies. A comparison with the predictions for the exclusive ${\eta }_c$ photoproduction, which is a direct probe of the Odderon, also is presented.

    hep-phhep-exPRD(2018)·22 citations
27. 27*

    Electromagnetic transitions of $(b\bar{c})$ bound system

    Sonali Patnaik🇮🇳 · P.C. Dash🇮🇳 · Susmita Kar🇮🇳 · N.Barik🇮🇳

    We study electromagnetic transitions: $B_c^{\ast }(ns)\to B_c(ns)e^{+}{e}^{-}$, $B_c^{\ast }(ns)\to B_c(n^{\prime }s)e^{+}{e}^{-}$ and $B_c(ns)\to B_c^{\ast }(n^{\prime }s)e^{+}{e}^{-}$ in the relativistic independent quark (RIQ) model based on a flavor-independent potential in the scalar-vector harmonic form. The transition form factors for energetically possible transitions involving $B_c$ - and $B_c^{\ast }$- mesons in ground as well as orbitally excited states are predicted in their respective kinematic range. Our predictions on decay width for the allowed and hindered transitions are found compatible with those of the model calculations based on Bethe-Salpeter approach. Predictions in this sector would not only provide more information about members of the $B_c$-family including mass splitting between vector mesons and corresponding pseudoscalar counterparts but give hints for experimental determination of unknown masses of other excited $B_c$ - and ground state of $B_c^{\ast }$-meson, which is expected at LHCb and $Z^0$ factory in near future.

    hep-phPRD(2018)·10 citations
28. 28*

    Nucleon Resonance Structure from Exclusive Meson Electroproduction with CLAS

    Victor I. Mokeev🇺🇸

    Studies of the nucleon resonance electroexcitation amplitudes in a wide range of photon virtualities offer unique information on many facets of strong QCD behind the generation of all prominent excited nucleon states. Advances in the evaluation of resonance electroexcitation amplitudes from the data measured with the CLAS detector and the future extension of these studies with the CLAS12 detector at Jefferson Lab are presented. For the first time, analyses of ${\pi }^{0}p$, ${\pi }^{+}n$, $\eta p$, and ${\pi }^{+}{\pi }^{-}p$ electroproduction off proton channels have provided electroexcitation amplitudes of most resonances in the mass range up to 1.8 GeV and at photon virtualities $Q^2<5$~GeV${}^2$.Studies of the resonance electroexcitation amplitudes revealed the $N^{\ast }$ structure as a complex interplay between the inner core of three dressed quarks and the external meson-baryon cloud. The successful description of the $\Delta (1232)3/2^{+}$ and $N(1440)1/2^{+}$ electrocouplings achieved within the Dyson-Schwinger Equation approach under a traceable connection to the QCD Lagrangian and supported by the novel light front quark model demonstrated the relevance of dressed quarks with dynamically generated masses as an active structural component in baryons. Future experiments with the CLAS12 detector will offer insight into the structure of all prominent resonances at the highest photon virtualities, $Q^2<12$~GeV${}^2$, ever achieved in exclusive reactions, thus addressing the most challenging problems of the Standard Model on the nature of hadron mass, quark-gluon confinement, and the emergence of nucleon resonance structures from QCD. A search for new states of hadronic matter, the so-called hybrid-baryons with glue as a structural component, will complete the long term efforts on the resonance spectrum exploration.

    ↳ nucl-exhep-phFew Body Syst.(2018)·26 citations
29. 29*

    $\Delta (1232)$-Resonance in the Hydrogen Spectrum

    Franziska Hagelstein (AEC Bern)🇨🇭

    The electromagnetic excitation of the $\Delta (1232)$-resonance plays an appreciable role in the Lamb shift and hyperfine structure of muonic and electronic hydrogen. Its effect appears at the subleading order $\mathcal{O}({\alpha }^5)$, together with other proton-polarizability contributions from forward two-photon exchange. We use the large-$N_c$ relations for the nucleon-to-delta transition form factors to compute the effect of the $\Delta (1232)$ in the hydrogen spectrum. We pay particular attention to a subtile difference between predictions based on a direct calculation of the two-photon exchange (or Compton scattering amplitudes) and predictions based on the $\Delta (1232)$-production photoabsorption cross sections. The mismatch is explained by studying the dispersion relations for tree-level Compton scattering off the proton in more details.

    ↳ nucl-thhep-phFew Body Syst.(2018)·16 citations
30. 30*

    Condition for confinement in non-Abelian gauge theories

    Masud Chaichian🇫🇮 · Marco Frasca🇮🇹

    We show that a criterion for confinement, based on the BRST invariance, holds in four dimensions, by solving a non-Abelian gauge theory with a set of exact solutions. The confinement condition we consider was obtained by Kugo and Ojima some decades ago. The current understanding of gauge theories permits us to apply the techniques straightforwardly for checking the validity of this criterion. In this way, we are able to show that the non-Abelian gauge theory is confining and that confinement is rooted in the BRST invariance and asymptotic freedom.

    ↳ hep-thhep-phmath-phmath.MPPLB(2018)·31 citations
31. 31*

    Spectator electric fields, de Sitter space-time and the Schwinger effect

    Massimo Giovannini🇨🇭

    During a de Sitter stage of expansion the spectator fields of different spin are constrained by the critical density bound and by further requirements determined by their specific physical nature. The evolution of spectator electric fields in conformally flat background geometries is occasionally concocted by postulating the existence of ad hoc currents but this apparently innocuous trick violates the second law of thermodynamics. Such a problem occurs, in particular, for those configurations (customarily employed for the analysis of the Schwinger effect in four-dimensional de Sitter backgrounds) leading to an electric energy density which is practically unaffected by the expansion of the underlying geometry. The obtained results are compared with more mundane situations where Joule heating develops in the early stages of a quasi-de Sitter phase.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2018)·24 citations
32. 32*

    Is The Universal Matter - Antimatter Asymmetry Fine Tuned?

    Gary Steigman🇺🇸 · Robert J. Scherrer🇺🇸

    The asymmetry between matter and antimatter is key to the existence and nature of our Universe. A measure of the matter - antimatter asymmetry of the Universe is provided by the present value of the universal ratio of baryons (baryons minus antibaryons) to photons (or the ratio of baryons to entropy). The baryon asymmetry parameter is an important physical and cosmological parameter. But how fine tuned is it? A "natural" value for this parameter is zero, corresponding to equal amounts of matter and antimatter. Another, also possibly natural, choice for this dimensionless parameter would be of order unity, corresponding to nearly equal amounts (by number) of matter (and essentially no antimatter) and photons in every comoving volume. However, observations suggest that in the Universe we inhabit the value of this parameter is nonzero, but smaller than this natural value by some nine to ten orders of magnitude. In this contribution we review the evidence that our Universe does not contain equal amounts of matter and antimatter. Any change in the magnitude of the baryon asymmetry parameter necessarily leads to a universe with physical characteristics different from those in our own. The degree of fine tuning in the baryon asymmetry parameter is determined by the width of the range over which it can be varied and still allow for the existence of life. Our results suggest that the baryon asymmetry parameter can be varied over a very wide range without impacting the prospects for life; this result is not suggestive of fine tuning. [abridged]

    ↳ astro-ph.COhep-ph12 citations
33. 33*

    On chiral extrapolations of charmed meson masses and coupled-channel reaction dynamics

    Xiao-Yu Guo🇩🇪 · Yonggoo Heo🇩🇪 · Matthias F.M. Lutz🇩🇪

    We perform an analysis of QCD lattice data on charmed meson masses. The quark-mass dependence of the data set is used to gain information on the size of counter terms of the chiral Lagrangian formulated with open-charm states with J^P= 0^- and J^P =1^- quantum numbers. Of particular interest are those counter terms that are active in the exotic flavour sextet channel. A chiral expansion scheme where physical masses enter the extrapolation formulae is developed and applied to the lattice data set. Good convergence properties are demonstrated and an accurate reproduction of the lattice data based on ensembles of PACS-CS, MILC, ETMC and HSC with pion and kaon masses smaller than 600 MeV is achieved. It is argued that a unique set of low-energy parameters is obtainable only if additional information from HSC on some scattering observables is included in our global fits. The elastic and inelastic s-wave pi D and eta D scattering as considered by HSC is reproduced faithfully. Based on such low-energy parameters we predict 15 phase shifts and in-elasticities at physical quark masses but also for an additional HSC ensemble at smaller pion mass. In addition we find a clear signal for a member of the exotic flavour sextet states in the eta D channel, below the bar K D_s threshold. For the isospin violating strong decay width of the D_{s0}(2317) we obtain the range (104-116) keV.

    ↳ hep-lathep-phnucl-thPRD(2018)·85 citations
34. 34*

    Instanton liquid properties from lattice QCD

    A. Athenodorou🇨🇾 · Ph. Boucaud🇫🇷 · F. De Soto🇪🇸 · J. Rodríguez-Quintero🇪🇸 · S. Zafeiropoulos🇩🇪

    We examined the instanton contribution to the QCD configurations generated from lattice QCD for $N_F=0$, $N_F=2+1$ and $N_F=2+1+1$ dynamical quark flavors from two different and complementary approaches. First via the use of Gradient flow, we computed instanton liquid properties using an algorithm to localize instantons in the gauge field configurations and studied their evolution with flow time. Then, the analysis of the running at low momenta of gluon Green's functions serves as an independent confirmation of the instanton density which can also be derived without the use of the Gradient flow.

    ↳ hep-lathep-phJHEP(2018)·30 citations
35. 35*

    N* Experiments and their Impact on Strong QCD Physics

    Volker D. Burkert🇺🇸

    I give a brief overview of experimental studies of the spectrum and the structure of the excited states of the nucleon and what we learn about their internal structure. The focus is on the effort to obtain a more complete picture of the light-quark baryon excitation spectrum employing electromagnetic beams, and on the study of the transition form factors and helicity amplitudes and their dependence on the magnitude of the photon virtuality $Q^2$, especially for some of the most prominent resonances. The results were obtained in pion and eta electroproduction experiments off proton targets. They strengthen the connection of experiment and new results from modeling sQCD in DSE and Light Cone SR approaches. They also point to the nature of these states as 3-quark excitations at the core.

    ↳ nucl-exhep-phnucl-thFew Body Syst.(2018)·21 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.