Fri·Jan 15, 2016Friday·January 15, 2016

1. 01*

   Short-distance RG-analysis of $X(3872)$ radiative decays

   D. A. S. Molnar🇧🇷 · R. F. Luiz🇧🇷 · R. Higa🇧🇷

   We present a renormalization-group analysis of the $X(3872)$ radiative decays into $J/\psi \gamma$ and $\psi (2S)\gamma$. We assume a $D{\bar{D}}^{\ast }$ molecule for the $X$ long-distance structure and parametrize its short-distance physics as contact interactions. Using effective field theory techniques and power-divergence subtraction scheme, we find that short- and long-distance physics are equally important in these decays. Our calculations set a lower limit to the corresponding decay widths, which can in principle be tested experimentally. Our results may be used as guide to build models for the $X$ short-distance.

   hep-phnucl-th6 citations
2. 02*

   The impact of the final HERA combined data on PDFs obtained from a global fit

   L. A. Harland-Lang🇬🇧 · A. D. Martin🇬🇧 · P. Motylinski🇬🇧 · R. S. Thorne🇬🇧

   We investigate the effect of including the HERA run I + II combined cross section data on the MMHT2014 PDFs. We present the fit quality within the context of the global fit and when only the HERA data are included. We examine the changes in both the central values and uncertainties in the PDFs. We find that the prediction for the data is good, and only relatively small improvements in ${\chi }^2$ and changes in the PDFs are obtained with a refit at both NLO and NNLO. PDF uncertainties are slightly reduced. There is a small dependence of the fit quality on the value of $Q_{\min }^2$. This can be improved by phenomenologically motived corrections to $F_L(x,Q^2)$ which parametrically are largely in the form of higher-twist type contributions.

   hep-phEPJC(2016)·60 citations
3. 03*

   Reggeon-gluon vertices with Ward identities

   M.A. Braun🇷🇺 · M.I. Vyazovsky (Saint-Petersburg State University, Russia)🇷🇺

   Ward identities for reggeons are studied in the framework of effective action approach to the QCD in Regge kinematics. It is shown that they require introduction of new contributions not present in the reggeon diagrams initially. Application to vertices RR$\to$RP and RR$\to$RRP are considered and diagrams which have to be added to the QCD ones are found.

   hep-phhep-thPRD(2016)·13 citations
4. 04*

   Constraints on non-universal gaugino mass scenario using the latest LHC data

   J.Kawamura🇯🇵 · Y.Omura🇯🇵

   We investigate exclusion limits on the the non-universal gaugino mass scenario in the Minimal Supersymmetric Standard Model (MSSM), according the the latest results of the super-particle search at the LHC8 and the LHC13. In this scenario, suitable ratios of wino to gluino mass can realize the observed value of the Higgs boson mass, while keeping a small $\mu$ parameter. Such a small $\mu$ parameter corresponds to the mass of higgsino, so that lightest neutralino and chargino are higgsino-like and their masses are almost degenerate. Besides, we find that the right-handed top squark tends to be lighter than other sfermions and then the top squark search, where the top squark decays to a quark and higgsino, is relevant to our model. In our analysis, the exclusion limits are derived using the data of the top squark searches in the $bb+E_T^{\mathrm{miss}}$ and $tb+E_T^{\mathrm{miss}}$ channels. Furthermore, the exclusion limit on gluino mass, which is crucial to our scenario, is investigated as well. The analysis of the gluino is based on the data of the analysis with large missing energy and at least three b-tagged jets at the ATLAS experiment.

   hep-phhep-exPRD(2016)·12 citations
5. 05*

   Analytic derivation of the next-to-leading order proton structure function $F_2^p(x,Q^2)$ based on the Laplace transformation

   Hamzeh Khanpour🇮🇷 · Abolfazl Mirjalili🇮🇷 · S. Atashbar Tehrani🇮🇷

   An analytical solution based on the Laplace transformation technique for the DGLAP evolution equations is presented at next-to-leading order accuracy in perturbative QCD. This technique is also applied to extract the analytical solution for the proton structure function, $F_2^p(x,Q^2)$, in the Laplace $s$-space. We present the results for the separate parton distributions for all parton species, including valence quark densities, the anti-quark and strange sea parton distribution functions (PDFs), and the gluon distribution. We successfully compare the obtained parton distribution functions and the proton structure function with the results from {\tt GJR08} and {\tt KKT12} parametrization models as well as the $x$-space results using {\tt QCDnum} code. Our calculations show a very good agreement with the available theoretical models as well as the deep inelastic scattering (DIS) experimental data throughout the small and large values of $x$. The use of our analytical solution to extract the parton densities and the proton structure function is discussed in detail to justify the analysis method considering the accuracy and speed of calculations. Overall, the accuracy we obtain from the analytical solution using the inverse Laplace transform technique is found to be better than 1 part in 10${}^4$ to 10${}^5$. We also present a detailed QCD analysis of non-singlet structure functions using all available DIS data to perform global QCD fits. In this regard we employ the Jacobi polynomial approach to convert the results from Laplace $s$ space to Bjorken $x$ space. The extracted valence quark densities are also presented and compared to the {\tt JR14}, {\tt MMHT14}, {\tt NNPDF} and {\tt CJ15} PDFs sets. We evaluate the numerical effects of target mass corrections (TMCs) and higher twist (HT) terms on various structure functions, and compare fits to data with and without these corrections.

   hep-phPRC(2017)·50 citations
6. 06*

   W+W- + jet: compact analytic results

   John Campbell🇺🇸 · David Miller🇬🇧 · Tania Robens🇩🇪

   In the second run of the LHC, which started in April 2015, an accurate understanding of Standard Model processes is more crucial than ever. Processes including electroweak gauge bosons serve as standard candles for SM measurements, and equally constitute important background for BSM searches. We here present the NLO QCD virtual contributions to W+W- + jet in an analytic format obtained through unitarity methods and show results for the full process using an implementation into the Monte Carlo event generator MCFM. Phenomenologically, we investigate total as well as differential cross sections for the LHC with 14 TeV center-of-mass energy, as well as a future 100 TeV proton-proton machine. In the format presented here, the one-loop virtual contributions also serve as important ingredients in the calculation of W+W- pair production at NNLO.

   hep-phPoS(2016)·2 citations
7. 07*

   Resonant SIMP dark matter

   Soo-Min Choi🇰🇷 · Hyun Min Lee🇰🇷

   We consider a resonant SIMP dark matter in models with two singlet complex scalar fields charged under a local dark $U(1{)}_D$. After the $U(1{)}_D$ is broken down to a $Z_5$ discrete subgroup, the lighter scalar field becomes a SIMP dark matter which has the enhanced $3\to 2$ annihilation cross section near the resonance of the heavier scalar field. Bounds on the SIMP self-scattering cross section and the relic density can be fulfilled at the same time for perturbative couplings of SIMP. A small gauge kinetic mixing between the SM hypercharge and dark gauge bosons can be used to make SIMP dark matter in kinetic equilibrium with the SM during freeze-out.

   hep-phastro-ph.COPLB(2016)·54 citations
8. 08*

   Study on decays of $Z_c(4020)$ and $Z_c(3900)$ into $h_c+\pi$

   Hong-Wei Ke🇨🇳 · Xue-Qian Li🇨🇳

   At the invariant mass spectrum of $h_c{\pi }^{\pm }$ a new resonance $Z_c(4020)$ has been observed, however the previously confirmed $Z_c(3900)$ does not show up at this channel. In this paper we assume that $Z_c(3900)$ and $Z_c(4020)$ are molecular states of $D{\bar{D}}^{\ast }(D^{\ast }\bar{D})$ and $D^{\ast }{\bar{D}}^{\ast }$ respectively, then we calculate the transition rates of $Z_c(3900)\to h_c+\pi$ and $Z_c(4020)\to h_c+\pi$ in the light front model. Our results show that the partial width of $Z_c(3900)\to h_c+\pi$ is only three times smaller than that of $Z_c(4020)\to h_c+\pi$. $Z_c(4020)$ seems to be a molecular state, so if $Z_c(3900)$ is also a molecular state it should be observed in the portal $e^{+}{e}^{-}\to h_c{\pi }^{\pm }$ as long as the database is sufficiently large, by contrary if the future more precise measurements still cannot find $Z_c(3900)$ at $h_c{\pi }^{\pm }$ channel, the molecular assignment to $Z_c(3900)$ should be ruled out.

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

   Early quark production and approach to chemical equilibrium

   D. Gelfand🇩🇪 · F. Hebenstreit🇨🇭 · J. Berges🇩🇪

   We perform real-time lattice simulations of out-of-equilibrium quark production in non-Abelian gauge theory in 3+1-dimensions. Our simulations include the backreaction of quarks onto the dynamical gluon sector, which is particularly relevant for strongly correlated quarks. We observe fast isotropization and universal behavior of quarks and gluons at weak coupling and establish a quantitative connection to previous pure glue results. In order to understand the strongly correlated regime, we perform simulations for a large number of flavors and compare them to those obtained with two light quark flavors. By doing this we are able to provide estimates of the chemical equilibration time.

   hep-phhep-latnucl-thPRD(2016)·33 citations
10. 10*

    The 750 GeV diphoton LHC excess and Extra Z's in Heterotic-String Derived Models

    Alon E. Faraggi🇬🇧 · John Rizos🇬🇷

    The ATLAS and CMS collaborations recently recorded possible di-photon excess at 750 GeV and a less significant di-boson excess around 1.9 TeV. Such excesses may be produced in heterotic-string derived Z' models, where the di-photon excess may be connected with the Standard Model singlet scalar responsible for the Z' symmetry breaking, whereas the di-boson excess arises from production of the extra vector boson. Additional vector-like states in the string Z' model are instrumental to explain the relatively large width of the di-photon events and mandated by anomaly cancellation to be in the vicinity of the Z' breaking scale. Wilson line breaking of the non-Abelian gauge symmetries in the string models naturally gives rise to dark matter candidates. Future collider experiments will discriminate between the high-scale heterotic-string models, which preserve the perturbative unification paradigm indicated by the Standard Model data, versus the low scale string models. We also discuss the possibility for the production of the di-photon events with high scale $U(1{)}_{Z^{\prime }}$ breaking.

    hep-phhep-thEPJC(2016)·60 citations
11. 11*

    Event-by-event fluctuations in the medium-induced jet evolution

    Miguel A. Escobedo🇫🇷 · Edmond Iancu🇫🇷

    We develop the event-by-event picture of the gluon distribution produced via medium-induced gluon branching by an energetic jet which propagates through a dense QCD medium. A typical event is characterized by the production of a large number of soft gluons which propagate at large angles with respect to the jet axis and which collectively carry a substantial amount of energy. By explicitly computing 2-gluon correlations, we demonstrate the existence of large event-by-event fluctuations, which reflect the stochastic nature of the branching process. For the two quantities that we have investigated -- the energy loss at large angles and the soft gluon multiplicity --, the dispersion is parametrically as large as the respective expectation value. We identify interesting scaling laws, which suggest that the multiplicity distribution should exhibit KNO (Koba-Nielsen-Olesen) scaling. A similar scaling is known to hold for a jet branching in the vacuum, but the medium-induced distribution is found to be considerably broader. We predict that event-by-event measurements of the di-jet asymmetry in Pb+Pb collisions at the LHC should observe large fluctuations in the number of soft hadrons propagating at large angles and also in the total energy carried by these hadrons.

    hep-phhep-exnucl-thJHEP(2016)·26 citations
12. 12*

    Asking for an extra photon in Higgs production at the LHC and beyond

    Emidio Gabrielli🇮🇹 · Barbara Mele🇮🇹 · Fulvio Piccinini🇮🇹 · Roberto Pittau🇪🇸

    We study the inclusive production of a Higgs boson in association with a high-$p_T$ photon at the LHC, detailing the leading-order features of the main processes contributing to the $H\gamma$ final state. Requiring an extra hard photon in Higgs production upsets the cross-section hierarchy for the dominant channels. The $H\gamma$ inclusive production comes mainly from photons radiated in vector-boson fusion (VBF), which accounts for about 2/3 of the total rate, for $p_T^{\gamma ,j}>30$ GeV, at leading order. On the other hand, radiating a high-$p_T$ photon in the main top-loop Higgs channel implies an extra parton in the final state, which suppresses the production rate by a further ${\alpha }_S$ power. As a result, the $H\gamma$ production via top loops at the LHC has rates comparable with the ones arising from either the $Ht\bar{t}$ production or the $HW(Z)\gamma$ associated production. Then, in order of decreasing cross section, comes the single-top-plus-Higgs channel, followed in turn by the heavy-flavor fusion processes $b\bar{b}\to H\gamma$ and $c\bar{c}\to H\gamma$. The $H\gamma$ production via electroweak loops has just a minor role. At larger c.m. energies, the $Ht\bar{t}\gamma$ channel surpasses the total contribution of top-loop processes. In particular, requiring $p_T^{\gamma ,j}>30$ GeV at $\sqrt{S}\simeq 100$ TeV, $Ht\bar{t}\gamma$ accounts for about $1/4$ of the inclusive $H\gamma$ production at leading order, about half of the total being due to VBF production.

    hep-phhep-exJHEP(2016)·22 citations
13. 13*

    A walk on sunset boulevard

    Luise Adams🇩🇪 · Christian Bogner🇩🇪 · Stefan Weinzierl🇩🇪

    A walk on sunset boulevard can teach us about transcendental functions associated to Feynman diagrams. On this guided tour we will see multiple polylogarithms, differential equations and elliptic curves. A highlight of the tour will be the generalisation of the polylogarithms to the elliptic setting and the all-order solution for the sunset integral in the equal mass case.

    hep-phhep-thmath-phmath.MPPoS(2016)·12 citations
14. 14*

    Latest theory developments for top pair production, generators and showering

    Emanuele Re🇬🇧

    I summarize the state of the art of cross-section computations and of available simulation tools for top-quark pair production in hadron collisions. Particular emphasis is put on recent theory developments relevant for LHC phenomenology.

    hep-phPoS(2016)·3 citations
15. 15*

    Search for Sphalerons in Proton-Proton Collisions

    John Ellis🇬🇧 · Kazuki Sakurai🇬🇧

    In a recent paper, Tye and Wong (TW) have argued that sphaleron-induced transitions in high-energy proton-proton collisions should be enhanced compared to previous calculations, based on a construction of a Bloch wave function in the periodic sphaleron potential and the corresponding pass band structure. Here we convolute the calculations of TW with parton distribution functions and simulations of final states to explore the signatures of sphaleron transitions at the LHC and possible future colliders. We calculate the increase of sphaleron transition rates in proton-proton collisions at centre-of-mass energies of 13/14/33/100 TeV for different sphaleron barrier heights, while recognising that the rates have large overall uncertainties. We use a simulation to show that LHC searches for microscopic black holes should have good efficiency for detecting sphaleron-induced final states, and discuss their experimental signatures and observability in Run 2 of the LHC and beyond. We recast the early ATLAS Run-2 search for microscopic black holes to constrain the rate of sphaleron transitions at 13 TeV, deriving a significant limit on the sphaleron transition rate for the nominal sphaleron barrier height of 9 TeV.

    hep-phhep-exJHEP(2016)·45 citations
16. 16*

    Higher-order corrections to the splitting functions from differential equations in QCD

    O.Gituliar🇵🇱

    We report on the status an ab initio computation of the time-like splitting functions at next-to-next-to-leading order in QCD. Time-like splitting functions govern the collinear kinematics of inclusive hadron production in $e^{+}{e}^{-}$ annihilation and the evolution of the parton fragmentation distributions. Current knowledge about them at three loops has been inferred by means of crossing symmetry from their related space-like counterparts, the deep-inelastic structure functions and parton densities. In this approach certain parts of the off-diagonal quark-gluon splitting function are left undetermined, which calls for an independent calculation from first principles. We outline the method for calculating master integrals from differential equations which are required to attack the problem.

    hep-phPoS(2016)·0 citations
17. 17*

    NLO-QCD corrections to Higgs pair production in the MSSM

    A. Agostini🇮🇹 · G. Degrassi🇮🇹 · R. Gröber🇮🇹 · P. Slavich🇫🇷

    We take a step towards a complete NLO-QCD determination of the production of a pair of Higgs scalars in the MSSM. Exploiting a low-energy theorem that connects the Higgs-gluon interactions to the derivatives of the gluon self-energy, we obtain analytic results for the one- and two-loop squark contributions to Higgs pair production in the limit of vanishing external momenta. We find that the two-loop squark contributions can have non-negligible effects in MSSM scenarios with stop masses below the TeV scale. We also show how our results can be adapted to the case of Higgs pair production in the NMSSM.

    hep-phJHEP(2016)·29 citations
18. 18*

    Future Collider Signatures of the Possible 750 GeV State

    Abdelhak Djouadi🇫🇷 · John Ellis🇬🇧 · Rohini Godbole🇮🇳 · Jérémie Quevillon🇬🇧

    If the recent indications of a possible state $\Phi$ with mass $\sim 750$ GeV decaying into two photons reported by ATLAS and CMS in LHC collisions at 13 TeV were to become confirmed, the prospects for future collider physics at the LHC and beyond would be affected radically, as we explore in this paper. Even minimal scenarios for the $\Phi$ resonance and its $\gamma \gamma$ decays require additional particles with masses $\gtrsim \frac{1}{2}{m}_{\Phi }$. We consider here two benchmark scenarios that exemplify the range of possibilities: one in which $\Phi$ is a singlet scalar or pseudoscalar boson whose production and $\gamma \gamma$ decays are due to loops of coloured and charged fermions, and another benchmark scenario in which $\Phi$ is a superposition of (nearly) degenerate CP-even and CP-odd Higgs bosons in a (possibly supersymmetric) two-Higgs doublet model also with additional fermions to account for the $\gamma \gamma$ decay rate. We explore the implications of these benchmark scenarios for the production of $\Phi$ and its new partners at colliders in future runs of the LHC and beyond, at higher-energy $pp$ colliders and at $e^{+}{e}^{-}$ and $\gamma \gamma$ colliders, with emphasis on the bosonic partners expected in the doublet scenario and the fermionic partners expected in both scenarios.

    hep-phhep-exJHEP(2016)·81 citations
19. 19*

    UV Corrections in Sgoldstino-less Inflation

    Emilian Dudas🇫🇷 · Lucien Heurtier🇧🇪 · Clemens Wieck🇪🇸 · Martin Wolfgang Winkler🇩🇪

    We study the embedding of inflation with nilpotent multiplets in supergravity, in particular the decoupling of the sgoldstino scalar field. Instead of being imposed by hand, the nilpotency constraint on the goldstino multiplet arises in the low energy-effective theory by integrating out heavy degrees of freedom. We present explicit supergravity models in which a large but finite sgoldstino mass arises from Yukawa or gauge interactions. In both cases the inflaton potential receives two types of corrections. One is from the backreaction of the sgoldstino, the other from the heavy fields generating its mass. We show that these scale oppositely with the Volkov-Akulov cut-off scale, which makes a consistent decoupling of the sgoldstino nontrivial. Still, we identify a parameter window in which sgoldstino-less inflation can take place, up to corrections which flatten the inflaton potential.

    ↳ hep-thastro-ph.COhep-phPLB(2016)·22 citations
20. 20*

    Solitonic modulation and Lifshitz point in an external magnetic field within Nambu--Jona-Lasinio model

    Gaoqing Cao🇨🇳 · Anping Huang🇨🇳

    We study the inhomogeneous solitonic modulation of a chiral condensate within the effective Nambu--Jona-Lasinio model when a constant external magnetic field is present. The self-consistent Pauli-Villars regularization scheme is adopted to manipulate the ultraviolet divergence encountered in the thermodynamic quantities. In order to determine the chiral restoration lines efficiently, a new kind of Ginzburg-Landau expansion approach is proposed here. At zero temperature, we find that both the upper and lower boundaries of the solitonic modulation oscillate with the magnetic field in the $\mu$--$B$ phase diagram which is actually the de Hass-van Alphan (dHvA) oscillation. It is very interesting to find out how the tricritical Lifshitz point $(T_L,{\mu }_L)$ evolves with the magnetic field: There are also dHvA oscillations in the $T_L$--$B$ and ${\mu }_L$--$B$ curves, though the tricritical temperature $T_L$ increases monotonically with the magnetic field.

    ↳ nucl-thhep-phhep-thPRD(2016)·17 citations
21. 21*

    Statistical anisotropy from inflationary magnetogenesis

    Massimo Giovannini🇨🇭

    Provided the quantum fluctuations are amplified in the presence of a classical gauge field configuration the resulting curvature perturbations exhibit a mild statistical anisotropy which should be sufficiently weak not to conflict with current observational data. The curvature power spectra induced by weakly anisotropic initial states are computed here for the first time when the electric and the magnetic gauge couplings evolve at different rates as it happens, for instance, in the relativistic theory of van der Waals interactions. After recovering the results valid for coincident gauge couplings, the constraints imposed by the isotropy and the homogeneity of the initial states are discussed. The obtained bounds turn out to be more stringent than naively expected and cannot be ignored when discussing the underlying magnetogenesis scenarios.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2016)·6 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.