Abstract
We propose a LHC search for dilepton resonances in association with large missing energy as a generic probe of TeV dark sector models. Such resonances can occur if the dark sector includes a U(1) gauge boson, or Z′, which kinetically mixes with the Standard Model U(1). For small mixing, direct 2 → 1 production of the Z′ is not visible in standard resonance searches due to the large Drell-Yan background. However, there may be significant production of the Z′ boson in processes involving other dark sector particles, resulting in final states with a Z′ resonance and missing transverse momentum. Examples of such processes include cascade decays within the dark sector and radiation of the Z′ off of final state dark sector particles. Even when the rate to produce a Z′ boson in a dark sector process is suppressed, this channel can provide better sensitivity than traditional collider probes of dark sectors such as monojet searches. We find that data from the 8 TeV LHC run can be interpreted to give bounds on such processes; more optimized searches could extend the sensitivity and continue to probe these models in the Run II data.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Planck collaboration, P.A.R. Ade et al., Planck 2015 results. XIII. Cosmological parameters, arXiv:1502.01589 [INSPIRE].
G. Jungman, M. Kamionkowski and K. Griest, Supersymmetric dark matter, Phys. Rept. 267 (1996) 195 [hep-ph/9506380] [INSPIRE].
CMS collaboration, Search for dark matter, extra dimensions and unparticles in monojet events in proton-proton collisions at \( \sqrt{s}=8 \) TeV, Eur. Phys. J. C 75 (2015) 235 [arXiv:1408.3583] [INSPIRE].
ATLAS collaboration, Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector, Eur. Phys. J. C 75 (2015) 299 [arXiv:1502.01518] [INSPIRE].
CMS collaboration, Search for new phenomena in monophoton final states in proton-proton collisions at \( \sqrt{s}=8 \) TeV, arXiv:1410.8812 [INSPIRE].
ATLAS collaboration, Search for dark matter in events with a hadronically decaying W or Z boson and missing transverse momentum in pp collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector, Phys. Rev. Lett. 112 (2014) 041802 [arXiv:1309.4017] [INSPIRE].
ATLAS collaboration, Search for new particles in events with one lepton and missing transverse momentum in pp collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector, JHEP 09 (2014) 037 [arXiv:1407.7494] [INSPIRE].
ATLAS collaboration, Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector, Phys. Rev. D 91 (2015) 012008 [arXiv:1411.1559] [INSPIRE].
CMS collaboration, Search for physics beyond the standard model in final states with a lepton and missing transverse energy in proton-proton collisions at \( \sqrt{s}=8 \) TeV, Phys. Rev. D 91 (2015) 092005 [arXiv:1408.2745] [INSPIRE].
J. Goodman, M. Ibe, A. Rajaraman, W. Shepherd, T.M.P. Tait and H.-B. Yu, Constraints on Dark Matter from Colliders, Phys. Rev. D 82 (2010) 116010 [arXiv:1008.1783] [INSPIRE].
P.J. Fox, R. Harnik, J. Kopp and Y. Tsai, LEP Shines Light on Dark Matter, Phys. Rev. D 84 (2011) 014028 [arXiv:1103.0240] [INSPIRE].
P.J. Fox, R. Harnik, J. Kopp and Y. Tsai, Missing Energy Signatures of Dark Matter at the LHC, Phys. Rev. D 85 (2012) 056011 [arXiv:1109.4398] [INSPIRE].
P.J. Fox, R. Harnik, R. Primulando and C.-T. Yu, Taking a Razor to Dark Matter Parameter Space at the LHC, Phys. Rev. D 86 (2012) 015010 [arXiv:1203.1662] [INSPIRE].
Y. Bai and T.M.P. Tait, Searches with Mono-Leptons, Phys. Lett. B 723 (2013) 384 [arXiv:1208.4361] [INSPIRE].
N.F. Bell, J.B. Dent, A.J. Galea, T.D. Jacques, L.M. Krauss and T.J. Weiler, Searching for Dark Matter at the LHC with a Mono-Z, Phys. Rev. D 86 (2012) 096011 [arXiv:1209.0231] [INSPIRE].
L.M. Carpenter, A. Nelson, C. Shimmin, T.M.P. Tait and D. Whiteson, Collider searches for dark matter in events with a Z boson and missing energy, Phys. Rev. D 87 (2013) 074005 [arXiv:1212.3352] [INSPIRE].
J.-Y. Chen, E.W. Kolb and L.-T. Wang, Dark matter coupling to electroweak gauge and Higgs bosons: an effective field theory approach, Phys. Dark Univ. 2 (2013) 200 [arXiv:1305.0021] [INSPIRE].
H. Dreiner, D. Schmeier and J. Tattersall, Contact Interactions Probe Effective Dark Matter Models at the LHC, Europhys. Lett. 102 (2013) 51001 [arXiv:1303.3348] [INSPIRE].
A. Askew, S. Chauhan, B. Penning, W. Shepherd and M. Tripathi, Searching for Dark Matter at Hadron Colliders, Int. J. Mod. Phys. A 29 (2014) 1430041 [arXiv:1406.5662] [INSPIRE].
A. Berlin, T. Lin and L.-T. Wang, Mono-Higgs Detection of Dark Matter at the LHC, JHEP 06 (2014) 078 [arXiv:1402.7074] [INSPIRE].
A.A. Petrov and W. Shepherd, Searching for dark matter at LHC with Mono-Higgs production, Phys. Lett. B 730 (2014) 178 [arXiv:1311.1511] [INSPIRE].
T. Lin, E.W. Kolb and L.-T. Wang, Probing dark matter couplings to top and bottom quarks at the LHC, Phys. Rev. D 88 (2013) 063510 [arXiv:1303.6638] [INSPIRE].
A. Birkedal, K. Matchev and M. Perelstein, Dark matter at colliders: A Model independent approach, Phys. Rev. D 70 (2004) 077701 [hep-ph/0403004] [INSPIRE].
Y. Bai, P.J. Fox and R. Harnik, The Tevatron at the Frontier of Dark Matter Direct Detection, JHEP 12 (2010) 048 [arXiv:1005.3797] [INSPIRE].
J. Goodman, M. Ibe, A. Rajaraman, W. Shepherd, T.M.P. Tait and H.-B. Yu, Constraints on Light Majorana dark Matter from Colliders, Phys. Lett. B 695 (2011) 185 [arXiv:1005.1286] [INSPIRE].
K. Cheung, P.-Y. Tseng, Y.-L.S. Tsai and T.-C. Yuan, Global Constraints on Effective Dark Matter Interactions: Relic Density, Direct Detection, Indirect Detection and Collider, JCAP 05 (2012) 001 [arXiv:1201.3402] [INSPIRE].
S. Arrenberg et al., Dark Matter in the Coming Decade: Complementary Paths to Discovery and Beyond, arXiv:1310.8621 [INSPIRE].
S. Malik et al., Interplay and Characterization of Dark Matter Searches at Colliders and in Direct Detection Experiments, arXiv:1409.4075 [INSPIRE].
H. An, L.-T. Wang and H. Zhang, Dark matter with t-channel mediator: a simple step beyond contact interaction, Phys. Rev. D 89 (2014) 115014 [arXiv:1308.0592] [INSPIRE].
Y. Bai and J. Berger, Fermion Portal Dark Matter, JHEP 11 (2013) 171 [arXiv:1308.0612] [INSPIRE].
A. DiFranzo, K.I. Nagao, A. Rajaraman and T.M.P. Tait, Simplified Models for Dark Matter Interacting with Quarks, JHEP 11 (2013) 014 [Erratum ibid. 1401 (2014) 162] [arXiv:1308.2679] [INSPIRE].
S. Chang, R. Edezhath, J. Hutchinson and M. Luty, Effective WIMPs, Phys. Rev. D 89 (2014) 015011 [arXiv:1307.8120] [INSPIRE].
C. Cheung and D. Sanford, Simplified Models of Mixed Dark Matter, JCAP 02 (2014) 011 [arXiv:1311.5896] [INSPIRE].
M. Papucci, A. Vichi and K.M. Zurek, Monojet versus the rest of the world I: t-channel models, JHEP 11 (2014) 024 [arXiv:1402.2285] [INSPIRE].
A. Alves, S. Profumo and F.S. Queiroz, The dark Z′ portal: direct, indirect and collider searches, JHEP 04 (2014) 063 [arXiv:1312.5281] [INSPIRE].
A. Alves, A. Berlin, S. Profumo and F.S. Queiroz, Dark Matter Complementarity and the Z′ Portal, arXiv:1501.03490 [INSPIRE].
R. Primulando, E. Salvioni and Y. Tsai, The Dark Penguin Shines Light at Colliders, JHEP 07 (2015) 031 [arXiv:1503.04204] [INSPIRE].
M.T. Frandsen, F. Kahlhoefer, A. Preston, S. Sarkar and K. Schmidt-Hoberg, LHC and Tevatron Bounds on the Dark Matter Direct Detection Cross-Section for Vector Mediators, JHEP 07 (2012) 123 [arXiv:1204.3839] [INSPIRE].
M. Chala, F. Kahlhoefer, M. McCullough, G. Nardini and K. Schmidt-Hoberg, Constraining Dark Sectors with Monojets and Dijets, JHEP 07 (2015) 089 [arXiv:1503.05916] [INSPIRE].
M.J. Strassler and K.M. Zurek, Echoes of a hidden valley at hadron colliders, Phys. Lett. B 651 (2007) 374 [hep-ph/0604261] [INSPIRE].
T. Han, Z. Si, K.M. Zurek and M.J. Strassler, Phenomenology of hidden valleys at hadron colliders, JHEP 07 (2008) 008 [arXiv:0712.2041] [INSPIRE].
B. Holdom, Two U(1)’s and Epsilon Charge Shifts, Phys. Lett. B 166 (1986) 196 [INSPIRE].
CMS collaboration, Search for physics beyond the standard model in dilepton mass spectra in proton-proton collisions at \( \sqrt{s}=8 \) TeV, JHEP 04 (2015) 025 [arXiv:1412.6302] [INSPIRE].
ATLAS collaboration, Search for high-mass dilepton resonances in pp collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector, Phys. Rev. D 90 (2014) 052005 [arXiv:1405.4123] [INSPIRE].
D0 collaboration, V.M. Abazov et al., Search for a heavy neutral gauge boson in the dielectron channel with 5.4 fb −1 of pp collisions at \( \sqrt{s}=1.96 \) TeV, Phys. Lett. B 695 (2011) 88 [arXiv:1008.2023] [INSPIRE].
CDF collaboration, Search for High Mass Resonances Decaying to Muon Pairs in \( \sqrt{s}=1.96 \) TeV \( p\overline{p} \) Collisions, Phys. Rev. Lett. 106 (2011) 121801 [arXiv:1101.4578] [INSPIRE].
CMS collaboration, Measurement of W+W- and ZZ production cross sections in pp collisions at \( \sqrt{s}=8 \) TeV, Phys. Lett. B 721 (2013) 190 [arXiv:1301.4698] [INSPIRE].
CMS collaboration, Measurement of the W + W − Cross section in pp Collisions at \( \sqrt{s}=7 \) TeV and Limits on Anomalous WWγ and WWZ couplings, Eur. Phys. J. C 73 (2013) 2610 [arXiv:1306.1126] [INSPIRE].
ATLAS collaboration, Measurement of W + W − production in pp collisions at \( \sqrt{s}=7 \) TeV with the ATLAS detector and limits on anomalous WWZ and WWγ couplings, Phys. Rev. D 87 (2013) 112001 [arXiv:1210.2979] [INSPIRE].
ATLAS collaboration, Search for direct production of charginos, neutralinos and sleptons in final states with two leptons and missing transverse momentum in pp collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector, JHEP 05 (2014) 071 [arXiv:1403.5294] [INSPIRE].
ATLAS collaboration, Electron performance measurements with the ATLAS detector using the 2010 LHC proton-proton collision data, Eur. Phys. J. C 72 (2012) 1909 [arXiv:1110.3174] [INSPIRE].
ATLAS collaboration, Measurement of the muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton-proton collision data, Eur. Phys. J. C 74 (2014) 3130 [arXiv:1407.3935] [INSPIRE].
CMS collaboration, Energy Calibration and Resolution of the CMS Electromagnetic Calorimeter in pp Collisions at \( \sqrt{s}=7 \) TeV, 2013 JINST 8 P09009 [arXiv:1306.2016] [INSPIRE].
CMS collaboration, Performance of CMS muon reconstruction in pp collision events at \( \sqrt{s}=7 \) TeV, 2012 JINST 7 P10002 [arXiv:1206.4071] [INSPIRE].
ATLAS collaboration, Search for the Standard Model Higgs boson decay to μ + μ − with the ATLAS detector, Phys. Lett. B 738 (2014) 68 [arXiv:1406.7663] [INSPIRE].
K.R. Dienes, C.F. Kolda and J. March-Russell, Kinetic mixing and the supersymmetric gauge hierarchy, Nucl. Phys. B 492 (1997) 104 [hep-ph/9610479] [INSPIRE].
J. Jaeckel and A. Ringwald, The Low-Energy Frontier of Particle Physics, Ann. Rev. Nucl. Part. Sci. 60 (2010) 405 [arXiv:1002.0329] [INSPIRE].
J. Hewett et al., Fundamental Physics at the Intensity Frontier, arXiv:1205.2671 [INSPIRE].
R. Essi et al., Dark Sectors and New, Light, Weakly-Coupled Particles, arXiv:1311.0029 [INSPIRE].
N. Arkani-Hamed and N. Weiner, LHC Signals for a SuperUnified Theory of Dark Matter, JHEP 12 (2008) 104 [arXiv:0810.0714] [INSPIRE].
M. Baumgart, C. Cheung, J.T. Ruderman, L.-T. Wang and I. Yavin, Non-Abelian Dark Sectors and Their Collider Signatures, JHEP 04 (2009) 014 [arXiv:0901.0283] [INSPIRE].
R. Essig, J. Kaplan, P. Schuster and N. Toro, On the Origin of Light Dark Matter Species, Submitted to: Physical Review D (2010) [arXiv:1004.0691] [INSPIRE].
S.A. Abel, M.D. Goodsell, J. Jaeckel, V.V. Khoze and A. Ringwald, Kinetic Mixing of the Photon with Hidden U(1)s in String Phenomenology, JHEP 07 (2008) 124 [arXiv:0803.1449] [INSPIRE].
M. Goodsell, S. Ramos-Sanchez and A. Ringwald, Kinetic Mixing of U(1)s in Heterotic Orbifolds, JHEP 01 (2012) 021 [arXiv:1110.6901] [INSPIRE].
M. Goodsell, J. Jaeckel, J. Redondo and A. Ringwald, Naturally Light Hidden Photons in LARGE Volume String Compactifications, JHEP 11 (2009) 027 [arXiv:0909.0515] [INSPIRE].
D. Curtin, R. Essig, S. Gori and J. Shelton, Illuminating Dark Photons with High-Energy Colliders, JHEP 02 (2015) 157 [arXiv:1412.0018] [INSPIRE].
A. Hook, E. Izaguirre and J.G. Wacker, Model Independent Bounds on Kinetic Mixing, Adv. High Energy Phys. 2011 (2011) 859762 [arXiv:1006.0973] [INSPIRE].
SLD Electroweak Group, SLD Heavy Flavor Group, DELPHI, LEP, ALEPH, OPAL, LEP Electroweak Working Group and L3 collaborations, A Combination of preliminary electroweak measurements and constraints on the standard model, hep-ex/0312023 [INSPIRE].
Particle Data Group collaboration, K. Olive et al., Review of Particle Physics, Chin. Phys. C 38 (2014) 090001.
J. Jaeckel, M. Jankowiak and M. Spannowsky, LHC probes the hidden sector, Phys. Dark Univ. 2 (2013) 111 [arXiv:1212.3620] [INSPIRE].
I. Hoenig, G. Samach and D. Tucker-Smith, Searching for dilepton resonances below the Z mass at the LHC, Phys. Rev. D 90 (2014) 075016 [arXiv:1408.1075] [INSPIRE].
N.F. Bell, J.B. Dent, T.D. Jacques and T.J. Weiler, Electroweak Bremsstrahlung in Dark Matter Annihilation, Phys. Rev. D 78 (2008) 083540 [arXiv:0805.3423] [INSPIRE].
M. Kachelriess, P.D. Serpico and M.A. Solberg, On the role of electroweak bremsstrahlung for indirect dark matter signatures, Phys. Rev. D 80 (2009) 123533 [arXiv:0911.0001] [INSPIRE].
CMS collaboration, Search for anomalous production of events with three or more leptons in pp collisions at \( \sqrt{s}=8 \) TeV, Phys. Rev. D 90 (2014) 032006 [arXiv:1404.5801] [INSPIRE].
G. Busoni, A. De Simone, E. Morgante and A. Riotto, On the Validity of the Effective Field Theory for Dark Matter Searches at the LHC, Phys. Lett. B 728 (2014) 412 [arXiv:1307.2253] [INSPIRE].
O. Buchmueller, M.J. Dolan and C. McCabe, Beyond Effective Field Theory for Dark Matter Searches at the LHC, JHEP 01 (2014) 025 [arXiv:1308.6799] [INSPIRE].
D. Racco, A. Wulzer and F. Zwirner, Robust collider limits on heavy-mediator Dark Matter, JHEP 05 (2015) 009 [arXiv:1502.04701] [INSPIRE].
Y. Cui, D.E. Morrissey, D. Poland and L. Randall, Candidates for Inelastic Dark Matter, JHEP 05 (2009) 076 [arXiv:0901.0557] [INSPIRE].
D. Curtin et al., Exotic decays of the 125 GeV Higgs boson, Phys. Rev. D 90 (2014) 075004 [arXiv:1312.4992] [INSPIRE].
S. Gopalakrishna, S. Jung and J.D. Wells, Higgs boson decays to four fermions through an abelian hidden sector, Phys. Rev. D 78 (2008) 055002 [arXiv:0801.3456] [INSPIRE].
H.-S. Lee and M. Sher, Dark Two Higgs Doublet Model, Phys. Rev. D 87 (2013) 115009 [arXiv:1303.6653] [INSPIRE].
A. Martin and T.S. Roy, The Gold-Plated Channel for Supersymmetric Higgs via Higgsphilic Z’, arXiv:1103.3504 [INSPIRE].
C.-F. Chang, E. Ma and T.-C. Yuan, Multilepton Higgs Decays through the Dark Portal, JHEP 03 (2014) 054 [arXiv:1308.6071] [INSPIRE].
CMS collaboration, Precise determination of the mass of the Higgs boson and tests of compatibility of its couplings with the standard model predictions using proton collisions at 7 and 8 TeV, Eur. Phys. J. C 75 (2015) 212 [arXiv:1412.8662] [INSPIRE].
ATLAS collaboration, Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC, Phys. Lett. B 726 (2013) 88 [Erratum ibid. B 734 (2014) 406] [arXiv:1307.1427] [INSPIRE].
Z. Chacko, H.-S. Goh and R. Harnik, The Twin Higgs: Natural electroweak breaking from mirror symmetry, Phys. Rev. Lett. 96 (2006) 231802 [hep-ph/0506256] [INSPIRE].
N. Craig, S. Knapen and P. Longhi, Neutral Naturalness from Orbifold Higgs Models, Phys. Rev. Lett. 114 (2015) 061803 [arXiv:1410.6808] [INSPIRE].
N. Craig, S. Knapen and P. Longhi, The Orbifold Higgs, JHEP 03 (2015) 106 [arXiv:1411.7393] [INSPIRE].
G. Burdman, Z. Chacko, H.-S. Goh and R. Harnik, Folded supersymmetry and the LEP paradox, JHEP 02 (2007) 009 [hep-ph/0609152] [INSPIRE].
N. Craig, A. Katz, M. Strassler and R. Sundrum, Naturalness in the Dark at the LHC, JHEP 07 (2015) 105 [arXiv:1501.05310] [INSPIRE].
R. Barbieri, T. Gregoire and L.J. Hall, Mirror world at the large hadron collider, hep-ph/0509242 [INSPIRE].
A. Falkowski, S. Pokorski and M. Schmaltz, Twin SUSY, Phys. Rev. D 74 (2006) 035003 [hep-ph/0604066] [INSPIRE].
S. Chang, L.J. Hall and N. Weiner, A Supersymmetric twin Higgs, Phys. Rev. D 75 (2007) 035009 [hep-ph/0604076] [INSPIRE].
N. Craig and K. Howe, Doubling down on naturalness with a supersymmetric twin Higgs, JHEP 03 (2014) 140 [arXiv:1312.1341] [INSPIRE].
CMS collaboration, Projected Performance of an Upgraded CMS Detector at the LHC and HL-LHC: Contribution to the Snowmass Process, arXiv:1307.7135 [INSPIRE].
M. Autran, K. Bauer, T. Lin and D. Whiteson, Searches for dark matter in events with a resonance and missing transverse energy, Phys. Rev. D 92 (2015) 035007 [arXiv:1504.01386] [INSPIRE].
Y. Bai, J. Bourbeau and T. Lin, Dark matter searches with a mono-Z′ jet, JHEP 06 (2015) 205 [arXiv:1504.01395] [INSPIRE].
J. Alwall, R. Frederix, S. Frixione, V. Hirschi, F. Maltoni, O. Mattelaer et al., The automated computation of tree-level and next-to-leading order differential cross sections and their matching to parton shower simulations, JHEP 07 (2014) 079 [arXiv:1405.0301] [INSPIRE].
A. Alloul, N.D. Christensen, C. Degrande, C. Duhr and B. Fuks, FeynRules 2.0 — A complete toolbox for tree-level phenomenology, Comput. Phys. Commun. 185 (2014) 2250 [arXiv:1310.1921] [INSPIRE].
T. Sjöstrand, S. Mrenna and P.Z. Skands, PYTHIA 6.4 Physics and Manual, JHEP 05 (2006) 026 [hep-ph/0603175] [INSPIRE].
DELPHES 3 collaboration, J. de Favereau et al., DELPHES 3, A modular framework for fast simulation of a generic collider experiment, JHEP 02 (2014) 057 [arXiv:1307.6346] [INSPIRE].
M. Cacciari, G.P. Salam and G. Soyez, FastJet User Manual, Eur. Phys. J. C 72 (2012) 1896 [arXiv:1111.6097] [INSPIRE].
M. Cacciari and G.P. Salam, Pileup subtraction using jet areas, Phys. Lett. B 659 (2008) 119 [arXiv:0707.1378] [INSPIRE].
M. Cacciari, G.P. Salam and G. Soyez, The Catchment Area of Jets, JHEP 04 (2008) 005 [arXiv:0802.1188] [INSPIRE].
CMS Collaboration, Pileup Jet Identification, CMS-PAS-JME-13-005 (2013).
J.M. Campbell, R.K. Ellis and C. Williams, Vector boson pair production at the LHC, JHEP 07 (2011) 018 [arXiv:1105.0020] [INSPIRE].
M. Czakon, P. Fiedler and A. Mitov, Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through \( O\left(\alpha \frac{4}{S}\right) \), Phys. Rev. Lett. 110 (2013) 252004 [arXiv:1303.6254] [INSPIRE].
Open Access
This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.
Author information
Authors and Affiliations
Corresponding author
Additional information
ArXiv ePrint: 1504.01385
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0), which permits use, duplication, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
About this article
Cite this article
Gupta, A., Primulando, R. & Saraswat, P. A new probe of dark sector dynamics at the LHC. J. High Energ. Phys. 2015, 79 (2015). https://doi.org/10.1007/JHEP09(2015)079
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/JHEP09(2015)079