Mon·Dec 14, 2015Monday·December 14, 2015

1. 01*

   Combination of Run-1 Exotic Searches in Diboson Final States at the LHC

   Flavia Dias🇬🇧 · Stefan Gadatsch🇨🇭 · Maxime Gouzevich🇫🇷 · Christos Leonidopoulos🇬🇧 · Sergio Novaes🇧🇷 · Alexandra Oliveira🇮🇹 · Maurizio Pierini🇨🇭 · Thiago Tomei🇧🇷

   We perform a statistical combination of the ATLAS and CMS results for the search of a heavy resonance decaying to a pair of vector bosons with the $\sqrt{s}=8$ TeV datasets collected at the LHC. We take into account six searches in hadronic and semileptonic final states carried out by the two collaborations. We consider only public information provided by ATLAS and CMS in the HEPDATA database and in papers published in refereed journals. We interpret the combined results within the context of a few benchmark new physics models, such as models predicting the existence of a {\ensuremath{\mathrm{W^\prime}}\xspace} or a bulk Randall-Sundrum spin--2 resonance, for which we present exclusion limits, significances, $p$-values and best-fit cross sections. A heavy diboson resonance with a production cross section of $\sim$4-5 fb and mass between 1.9 and 2.0 TeV is the exotic scenario most consistent with the experimental results. Models in which a heavy resonance decays preferentially to a WW final state are disfavoured.

   hep-phhep-exJHEP(2016)·23 citations
2. 02*

   Damping and Decoherence in Neutron Oscillations

   B.O. Kerbikov🇷🇺 · M.S. Lukashov🇷🇺 · Y.A. Kamyshkov🇺🇸 · L.J. Varriano🇺🇸

   An analysis is made of the role played by the gas environment in neutron-mirror-neutron and neutron-antineutron oscillations. In the first process the interaction with the ambient medium induces a refraction energy shift which plays the role of an extra magnetic field. In the second process antineutron annihilation in practice might lead to strong decoherence, which should be taken into account in experiments with free neutrons looking for the neutron to antineutron transformation.

   hep-ph8 citations
3. 03*

   Quark Condensate from Renormalization Group Optimized Spectral Density

   J.-L. Kneur🇫🇷 · A. Neveu🇫🇷

   Our renormalization group consistent variant of optimized perturbation, RGOPT, is used to calculate the nonperturbative QCD spectral density of the Dirac operator and the related chiral quark condensate $⟨\bar{q}q⟩$, for $n_f=2$ and $n_f=3$ massless quarks. Sequences of approximations at two-, three-, and four-loop orders are very stable and give $⟨\bar{q}q{⟩}_{n_f=2}^{1/3}(2\mathrm{GeV})=-(0.833-0.845){\bar{\Lambda }}_2$, and $⟨\bar{q}q{⟩}_{n_f=3}^{1/3}(2\mathrm{GeV})=-(0.814-0.838){\bar{\Lambda }}_3$ where the range is our estimated theoretical error and ${\bar{\Lambda }}_{n_f}$ the basic QCD scale in the $\overline{\mathrm{MS}}$-scheme. We compare those results with other recent determinations (from lattice calculations and spectral sum rules).

   hep-phhep-lathep-thNucl.Part.Phys.Proc.(2016)·1 citation
4. 04*

   The Flavor of the Composite Twin Higgs

   Csaba Csaki🇺🇸 · Michael Geller🇮🇱 · Ofri Telem🇮🇱 · Andreas Weiler🇩🇪

   The assumption of anarchic quark flavor puts serious stress on composite Higgs models: flavor bounds imply a tuning of a few per-mille (at best) in the Higgs potential. Composite twin Higgs (CTH) models significantly reduce this tension by opening up a new region of parameter space, obtained by raising the coupling among the composites close to the strong coupling limit $g_{\ast }\sim 4\pi$, thereby raising the scale of composites to around 10 TeV. This does not lead to large tuning in the Higgs potential since the leading quantum corrections are canceled by the twin partners (rather than the composites). We survey the leading flavor bounds on the CTH, which correspond to tree-level $\Delta F=2$ four-Fermi operators from Kaluza-Klein (KK) Z exchange in the kaon system and 1-loop corrections from KK fermions to the electric dipole moment of the neutron. We provide a parametric estimate for these bounds and also perform a numeric scan of the parameter space using the complete calculation for both quantities. The results confirm our expectation that CTH models accommodate anarchic flavor significantly better than regular composite Higgs (CH) models. Our conclusions apply both to the identical and fraternal twin cases.

   hep-phJHEP(2016)·51 citations
5. 05*

   Measuring the Higgs-bottom coupling in weak boson fusion

   Christoph Englert🇬🇧 · Olivier Mattelaer🇬🇧 · Michael Spannowsky🇬🇧

   We study Higgs production through weak boson fusion with subsequent decay to bottom quarks. By combining jet substructure techniques and matrix element methods in different limits we motivate this channel as a probe of the bottom-Yukawa interactions in the boosted regime. In particular we ameliorate the "no-go" results of cut-and-count analyses in this channel. After applying a data-driven reconstruction approach we find that the Higgs-bottom coupling can be limited to $0.82<y_b/y_b^{\text{SM}}<1.14$ with $600{\mathrm{fb}}^{-1}$.

   hep-phhep-exPLB(2016)·31 citations
6. 06*

   2, 84, 30, 993, 560, 15456, 11962, 261485, ...: Higher dimension operators in the SM EFT

   Brian Henning🇺🇸 · Xiaochuan Lu🇺🇸 · Tom Melia🇺🇸 · Hitoshi Murayama🇺🇸

   In a companion paper, we show that operator bases for general effective field theories are controlled by the conformal algebra. Equations of motion and integration by parts identities can be systematically treated by organizing operators into irreducible representations of the conformal group. In the present work, we use this result to study the standard model effective field theory (SM EFT), determining the content and number of higher dimension operators up to dimension 12, for an arbitrary number of fermion generations. We find additional operators to those that have appeared in the literature at dimension 7 (specifically in the case of more than one fermion generation) and at dimension 8. (The title sequence is the total number of independent operators in the SM EFT with one fermion generation, including hermitian conjugates, ordered in mass dimension, starting at dimension 5.)

   hep-phhep-thJHEP(2017)·375 citations
7. 07*

   Creating the Fermion Mass Hierarchies with Multiple Higgs Bosons

   Martin Bauer🇩🇪 · Marcela Carena🇺🇸 · Katrin Gemmler🇺🇸

   After the Higgs boson discovery, it is established that the Higgs mechanism explains electroweak symmetry breaking and generates the masses of all particles in the Standard Model, with the possible exception of neutrino masses. The hierarchies among fermion masses and mixing angles remain however unexplained. We propose a new class of two Higgs doublet models in which a flavor symmetry broken at the electroweak scale addresses this problem. The models are strongly constrained by electroweak precision tests and the fact that they produce modifications to Higgs couplings and flavor changing neutral currents; they are also constrained by collider searches for extra scalar bosons. The surviving models are very predictive, implying unavoidable new physics signals at the CERN Large Hadron Collider, e.g. extra Higgs Bosons with masses $M<700$ GeV.

   hep-phPRD(2016)·55 citations
8. 08*

   Reconciling $(g-2{)}_{\mu }$ and charged lepton flavour violating processes through a doubly charged scalar

   Joydeep Chakrabortty🇮🇳 · Pradipta Ghosh🇫🇷 · Subhadeep Mondal🇮🇳 · Tripurari Srivastava🇮🇳

   In this work, we investigate the phenomenological consequences of a doubly charged scalar which may belong to different uncoloured scalar multiplets. This doubly charged scalar couples to the charged leptons as well as gauge bosons, which we parametrize in a model independent way. Restricting ourselves in the regime of conserved charged-parity (CP), we assume only a few non-zero Yukawa couplings ($y_{\mu \ell }$, where $\ell =e,\mu ,\tau$) between the doubly charged scalar and the charged leptons. Our choices allow the doubly charged scalar to impinge low-energy processes like anomalous magnetic moment of muon and a few possible charged lepton flavour violating (CLFV) processes. These same Yukawa couplings are also instrumental in producing same-sign dilepton signatures at the LHC. In this article we examine the impact of individual contributions from the diagonal and off-diagonal Yukawa couplings in the light of muon $(g-2)$ excess. Subsequently, we use the derived information to inquire the possible CLFV processes and finally the collider signals from the decay of a doubly charged scalar. Our simplified analyses, depending on the mass of doubly charged scalar, provide a good estimate for the magnitude of the concerned Yukawa couplings. Our findings would appear resourceful to test the phenomenological significance of a doubly charged scalar by using complementary information from muon $(g-2)$, CLFV and the collider experiments.

   hep-phhep-exPRD(2016)·22 citations
9. 09*

   Effect of $Z_b$ states on ${\rm Y}(3S)\to {\rm Y}(1S)\pi \pi$ decays

   Yun-Hua Chen🇩🇪 · Johanna T. Daub🇩🇪 · Feng-Kun Guo🇨🇳 · Bastian Kubis🇩🇪 · Ulf-G. Meißner🇩🇪 · Bing-Song Zou🇨🇳

   Within the framework of dispersion theory, we analyze the dipion transitions between the lightest ${\rm Y}$ states, ${\rm Y}(nS)\to {\rm Y}(mS)\pi \pi$ with $m<n\le 3$. In particular, we consider the possible effects of two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$. The $\pi \pi$ rescattering effects are taken into account in a model-independent way using dispersion theory. We confirm that matching the dispersive representation to the leading chiral amplitude alone cannot reproduce the peculiar two-peak $\pi \pi$ mass spectrum of the decay ${\rm Y}(3S)\to {\rm Y}(1S)\pi \pi$. The existence of the bottomoniumlike $Z_b$ states can naturally explain this anomaly. We also point out the necessity of a proper extraction of the coupling strengths for the $Z_b$ states to ${\rm Y}(nS)\pi$, which is only possible if a Flatté-like parametrization is used in the data analysis for the $Z_b$ states.

   hep-phhep-exnucl-thPRD(2016)·60 citations
10. 10*

    The high-energy radiation pattern from BFKLex with double-log collinear contributions

    G. Chachamis🇪🇸 · A. Sabio Vera🇪🇸

    We study high-energy jet production in the multi-Regge limit making use of the Monte Carlo event generator BFKLex which includes collinear improvements in the form of double-log contributions as presented in [1]. Making use of the anti-kt jet algorithm in the FastJet implementation, we present results for the average transverse momentum and azimuthal angle of the produced jets when two tagged forward/backward jets are present in the final state. We also introduce a new observable which accounts for the average rapidity separation among subsequent emissions. Results are presented, for comparison, at leading order and next-to-leading order, with the resummation of collinear double logs proposed in [2].

    hep-phJHEP(2016)·40 citations
11. 11*

    $Z_c(3900)$: what has been really seen?

    Miguel Albaladejo🇪🇸 · Feng-Kun Guo🇨🇳 · Carlos Hidalgo-Duque🇪🇸 · Juan Nieves🇪🇸

    The $Z_c^{\pm }(3900)/Z_c^{\pm }(3885)$ resonant structure has been experimentally observed in the $Y(4260)\to J/\psi \pi \pi$ and $Y(4260)\to {\bar{D}}^{\ast }D\pi$ decays. This structure is intriguing since it is a prominent candidate of an exotic hadron. Yet, its nature is unclear so far. In this work, we simultaneously describe the ${\bar{D}}^{\ast }D$ and $J/\psi \pi$ invariant mass distributions in which the $Z_c$ peak is seen using amplitudes with exact unitarity. Two different scenarios are statistically acceptable, where the origin of the $Z_c$ state is different. They correspond to using energy dependent or independent ${\bar{D}}^{\ast }D$ $S$-wave interaction. In the first one, the $Z_c$ peak is due to a resonance with a mass around the $D{\bar{D}}^{\ast }$ threshold. In the second one, the $Z_c$ peak is produced by a virtual state which must have a hadronic molecular nature. In both cases the two observations, $Z_c^{\pm }(3900)$ and $Z_c^{\pm }(3885)$, are shown to have the same common origin, and a ${\bar{D}}^{\ast }D$ bound state solution is not allowed. Precise measurements of the line shapes around the $D{\bar{D}}^{\ast }$ threshold are called for in order to understand the nature of this state.

    hep-phnucl-thPLB(2016)·115 citations
12. 12*

    Prediction for CP Violation via Electric Dipole Moment of $\tau$ Lepton in $\gamma \gamma \to {\tau }^{+}{\tau }^{-}$ Process at CLIC

    S. Atag🇹🇷 · E. Gurkanli🇹🇷

    Pair production of tau leptons in two photon collision ${\gamma \gamma \to {\tau }^{+}\tau }^{-}$ is studied at CLIC to test CP violating QED couplings of tau leptons. CP violating effects are investigated using tau pair spin correlations which are observed through the hadronic decay of each $\tau$ into $\pi \nu$. Competitive bounds with previous works on the electric dipole moment from CP odd terms have been obtained.

    hep-phJHEP(2016)·19 citations
13. 13*

    The Phase Diagram of QC2D from Functional Methods

    Naseemuddin Khan🇩🇪 · Jan M. Pawlowski🇩🇪 · Fabian Rennecke🇩🇪 · Michael M. Scherer🇩🇪

    We study the phase diagram of two-color Quantum Chromodynamics at finite temperature and chemical potential. This is done within an effective low-energy description in terms of quarks, mesons and diquarks. Quantum, thermal and density fluctuations are taken into account with the functional renormalisation group approach. In particular, we establish the phenomenon of pre-condensation, affecting the location of the phase boundary to Bose-Einstein condensation. We also discuss the Silver Blaze property in the context of the functional renormalisation group.

    hep-phhep-thnucl-th64 citations
14. 14*

    Recent progress in some exclusive and semi-exclusive processes in proton-proton collisions

    Antoni Szczurek🇵🇱 · Anna Cisek🇵🇱 · Marta Luszczak🇵🇱 · Wolfgang Schafer🇵🇱

    We present the main results of our recent analyses of exclusive production of vector charmonia ($J/\psi$ and ${\psi }^{\prime }$) in $k_t$-factorization approach and for $\gamma \gamma$ production of charged dilepton pairs in exclusive and semiinclusive processes in a new approach, similar in spirit to $k_t$-factorization. The results for charmonia are compared with recent results of the LHCb collaboration. We include some helicity flip contributions and quantify the effect of absorption correction. The effect of $c\bar{c}$ wave function is illustrated. We present uncertainties related to $F_2$ structure function which are the main ingredient of the approach. Our results are compared with recent CMS data for dilepton production with lepton isolation cuts imposed.

    hep-phEPJ Web Conf.(2016)·0 citations
15. 15*

    Heavy Quark Diffusion in Strong Magnetic Fields at Weak Coupling and Implications for Elliptic Flow

    Kenji Fukushima🇯🇵 · Koichi Hattori🇯🇵 · Ho-Ung Yee🇺🇸 · Yi Yin🇺🇸

    We compute the momentum diffusion coefficients of heavy quarks, ${\kappa }_{\parallel }$ and ${\kappa }_{\perp }$, in a strong magnetic field $B$ along the directions parallel and perpendicular to $B$, respectively, at the leading order in QCD coupling constant ${\alpha }_s$. We consider a regime relevant for the relativistic heavy ion collisions, ${\alpha }_{s}eB\ll T^2\ll eB$, so that thermal excitations of light quarks are restricted to the lowest Landau level (LLL) states. In the vanishing light-quark mass limit, we find ${\kappa }_{\perp }^{\mathrm{LO}}\propto {\alpha }_s^{2}TeB$ in the leading order that arises from screened Coulomb scatterings with (1+1)-dimensional LLL quarks, while ${\kappa }_{\parallel }$ gets no contribution from the scatterings with LLL quarks due to kinematic restrictions. We show that the first non-zero leading order contributions to ${\kappa }_{\parallel }^{\mathrm{LO}}$ come from the two separate effects: 1) the screened Coulomb scatterings with thermal gluons, and 2) a finite light-quark mass $m_q$. The former leads to ${\kappa }_{\parallel }^{\mathrm{LO},\mathrm{gluon}}\propto {\alpha }_s^2{T}^3$ and the latter to ${\kappa }_{\parallel }^{\mathrm{LO},\mathrm{massive}}\propto {\alpha }_s({\alpha }_{s}eB{)}^{1/2}{m}_q^2$. Based on our results, we propose a new scenario for the large value of heavy-quark elliptic flow observed in RHIC and LHC. Namely, when ${\kappa }_{\perp }\gg {\kappa }_{\parallel }$, an anisotropy in drag forces gives rise to a sizable amount of the heavy-quark elliptic flow even if heavy quarks do not fully belong to an ellipsoidally expanding background fluid.

    hep-phnucl-thPRD(2016)·145 citations
16. 16*

    Inflation with an extra light scalar field after Planck

    Vincent Vennin🇬🇧 · Kazuya Koyama🇬🇧 · David Wands🇬🇧

    Bayesian inference techniques are used to investigate situations where an additional light scalar field is present during inflation and reheating. This includes (but is not limited to) curvaton-type models. We design a numerical pipeline where $\simeq 200$ inflaton setups $\times 10$ reheating scenarios $=2000$ models are implemented and we present the results for a few prototypical potentials. We find that single-field models are remarkably robust under the introduction of light scalar degrees of freedom. Models that are ruled out at the single-field level are not improved in general, because good values of the spectral index and the tensor-to-scalar ratio can only be obtained for very fine-tuned values of the extra field parameters and/or when large non-Gaussianities are produced. The only exception is quartic large-field inflation, so that the best models after Planck are of two kinds: plateau potentials, regardless of whether an extra field is added or not, and quartic large-field inflation with an extra light scalar field, in some specific reheating scenarios. Using Bayesian complexity, we also find that more parameters are constrained for the models we study than for their single-field versions. This is because the added parameters not only contribute to the reheating kinematics but also to the cosmological perturbations themselves, to which the added field contributes. The interplay between these two effects lead to a suppression of degeneracies that is responsible for having more constrained parameters.

    ↳ astro-ph.COhep-phhep-thJCAP(2016)·43 citations
17. 17*

    Can massive primordial black holes be produced in mild waterfall hybrid inflation?

    Masahiro Kawasaki🇯🇵 · Yuichiro Tada🇯🇵

    We studied the possibility whether the massive primordial black holes (PBHs) surviving today can be produced in hybrid inflation. Though it is of great interest since such PBHs can be the candidate for dark matter or seeds of the supermassive black holes in galaxies, there have not been quantitatively complete works yet because of the non-perturbative behavior around the critical point of hybrid inflation. Therefore, combining the stochastic and $\delta N$ formalism, we numerically calculated the curvature perturbations in a non-perturbative way and found, without any specific assumption of the types of hybrid inflation, PBHs are rather overproduced when the waterfall phase of hybrid inflation continues so long that the PBH scale is well enlarged and the corresponding PBH mass becomes sizable enough.

    ↳ astro-ph.COgr-qchep-phJCAP(2016)·86 citations
18. 18*

    Recent Results on Spectroscopy from COMPASS

    Boris Grube (for the COMPASS collaboration)🇩🇪

    The COmmon Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS) is a multi-purpose fixed-target experiment at the CERN Super Proton Synchrotron (SPS) aimed at studying the structure and spectrum of hadrons. The two-stage spectrometer has a good acceptance for charged as well as neutral particles over a wide kinematic range and is thus able to measure a wide range of reactions. Light mesons are studied with negative (mostly ${\pi }^{-}$) and positive ($p$, ${\pi }^{+}$) hadron beams with a momentum of 190 GeV/$c$. The light-meson spectrum is investigated in various final states produced in diffractive dissociation reactions at squared four-momentum transfers to the target between 0.1 and 1.0 (GeV/$c$)${}^2$. The flagship channel is the ${\pi }^{-}{\pi }^{+}{\pi }^{-}$ final state, for which COMPASS has recorded the currently largest data sample. These data not only allow for measuring the properties of known resonances with high precision, but also for searching for new states. Among these is a new resonance-like signal, the $a_1(1420)$, with unusual properties. The findings are confirmed by the analysis of the ${\pi }^{-}{\pi }^0{\pi }^0$ final state. Possible bias introduced by the parametrizations used to describe the $\pi \pi$ $S$-wave is studied using a novel analysis technique, which extracts the amplitude of the ${\pi }^{+}{\pi }^{-}$ sub-system as a function of $3\pi$ mass from the data. Of particular interest is the resonance content of the partial wave with spin-exotic $J^{PC}=1^{-+}$ quantum numbers, which are forbidden for quark-antiquark states. This wave is studied in the two $3\pi$ channels. Further insight is gained by studying diffractively produced ${\pi }^{-}\eta$ or ${\pi }^{-}{\eta }^{\prime }$ final states.

    ↳ hep-exhep-phAIP Conf.Proc.(2016)·2 citations
19. 19*

    Possible future HERA analyses

    Achim Geiser (DESY Hamburg)🇩🇪

    A variety of possible future analyses of HERA data in the context of the HERA data preservation programme is collected, motivated, and commented. The focus is placed on possible future analyses of the existing $ep$ collider data and their physics scope. Comparisons to the original scope of the HERA programme are made, and cross references to topics also covered by other participants of the workshop are given. This includes topics on QCD, proton structure, diffraction, jets, hadronic final states, heavy flavours, electroweak physics, and the application of related theory and phenomenology topics like NNLO QCD calculations, low-x related models, nonperturbative QCD aspects, and electroweak radiative corrections. Synergies with other collider programmes are also addressed. In summary, the range of physics topics which can still be uniquely covered using the existing data is very broad and of considerable physics interest, often matching the interest of results from colliders currently in operation. Due to well-established data and MC sets, calibrations, and analysis procedures the manpower and expertise needed for a particular analysis is often very much smaller than that needed for an ongoing experiment. Since centrally funded manpower to carry out such analyses is not available any longer, this contribution not only targets experienced self-funded experimentalists, but also theorists and master-level students who might wish to carry out such an analysis.

    ↳ hep-exhep-ph4 citations
20. 20*

    Linking neutrino oscillations to the nucleosynthesis of elements

    Meng-Ru Wu🇩🇪 · Gabriel Martinez-Pinedo🇩🇪 · Yong-Zhong Qian🇺🇸

    Neutrino interactions with matter play an important role in determining the nucleosynthesis outcome in explosive astrophysical environments such as core-collapse supernovae or mergers of compact objects. In this article, we first discuss our recent work on the importance of studying the time evolution of collective neutrino oscillations among active flavors in determining their effects on nucleosynthesis. We then consider the possible active-sterile neutrino mixing and demonstrate the need of a consistent approach to evolve neutrino flavor oscillations, matter composition, and the hydrodynamics when flavor oscillations can happen very deep inside the supernovae.

    ↳ astro-ph.HEhep-phnucl-thEPJ Web Conf.(2016)·9 citations
21. 21*

    Strangeness At Extremes

    Laura Tolos🇩🇪 · Daniel Cabrera🇩🇪 · Kanchan Khemchandani🇧🇷 · Alberto Martinez-Torres🇧🇷 · Elena Bratkovskaya🇩🇪 · Joerg Aichelin🇫🇷 · Marina Nielsen🇧🇷 · Fernando S. Navarra🇧🇷

    We study the properties of strange mesons in vacuum and in the hot nuclear medium within unitarized coupled-channel effective theories. We determine transition probabilities, cross sections and scattering lengths for strange mesons. These scattering observables are of fundamental importance for understanding the dynamics of strangeness production and propagation in heavy-ion collisions.

    ↳ nucl-thhep-phnucl-exJPS Conf.Proc.(2017)·0 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.