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Diphoton resonance at 750 GeV in supersymmetry
https://cds.cern.ch/record/2161346
The recent diphoton resonance at 750 GeV is studied in a supersymmetric context, using an effective theory approach. Since minimal supersymmetric models cannot give an explanation for this resonance we consider the MSSM extended by effective operators. From all operators of dimensions d=5 and d=6 beyond the MSSM Higgs sector, an effective operator of d=6 is identified as the only leading operator that contributes to this process, with the neutral CP-even (odd) H (A) as resonance or with both (mass degenerate). Both the $b\bar b$ and $gg$ production mechanisms are considered to contribute. The model accommodates a narrow resonance $\Gamma_X\approx 5$ GeV at low $\tan\beta\approx 10$ (where $gg$ production dominates) and also a broader one, up to $\Gamma_X \approx 25$ GeV at intermediate $\tan\beta=26$ in the mass degenerate case, while still respecting current bounds on $h\gamma\gamma$ and $h gg$ couplings of the SM-like higgs ($h$). A broader resonance $\Gamma_X=45$ GeV as reported by ATLAS only (reached at $\tan\beta\approx 36$ where $b\bar b$ production dominates), conflicts with an upper bound on $\Gamma_{X -> b\bar b}/\Gamma_{X -> \gamma\gamma}$ (X=A, H) and on $b\bar b$ cross section, inferred from the 8 TeV data scaled to 13 TeV. Ways to generate the effective operator from microscopic (renormalizable) models are presented. These favour the presence of new, TeV-scale vector-like states and eventually a massive gauge singlet beyond the MSSM spectrum.Ghilencea, D MLee, Hyun MinThu, 16 Jun 2016 06:33:37 GMT13 Jun 2016arXiv:1606.04131https://cds.cern.ch/record/2161346['arXiv:1606.04131']arXiv:1606.04131The diphoton as the Higgs of the Higgs
https://cds.cern.ch/record/2156480
LHC results do not confirm conventional natural solutions to the Higgs mass hierarchy problem, motivating alternative interpretations where a hierarchically small weak scale is generated from a dimension-less quantum dynamics. We propose weakly and strongly-coupled models where the field that breaks scale invariance giving mass to itself and to the Higgs is identified with the 750 GeV diphoton resonance. Such models can be extrapolated up to the Planck scale, provide Dark Matter candidates and eliminate the SM vacuum instability.Kannike, KristjanPelaggi, Giulio MariaSalvio, AlbertoStrumia, AlessandroMon, 30 May 2016 05:28:11 GMT27 May 2016arXiv:1605.08681https://cds.cern.ch/record/2156480['arXiv:1605.08681']arXiv:1605.08681QCD corrections to vector boson pair production in gluon fusion including interference effects with off-shell Higgs at the LHC
https://cds.cern.ch/record/2153477
We compute next-to-leading order (NLO) QCD corrections to the production of two massive electroweak bosons in gluon fusion. We consider both the prompt production process $gg \to VV$ and the production mediated by an exchange of an s-channel Higgs boson, $gg \to H^* \to V V$. We include final states with both on- and off-shell vector bosons with leptonic decays. The gluonic production of vector bosons is a loop-induced process, including both massless and massive quarks in the loop. For $gg \to ZZ$ production, we obtain the NLO QCD corrections to the massive loops through an expansion around the heavy top limit. This approximation is valid below the top production threshold, giving a broad range of invariant masses between the Higgs production and the top production thresholds in which our results are valid. We explore the NLO QCD effects in $gg \to ZZ$ focusing, in particular, on the interference between prompt and Higgs-mediated processes. We find that the QCD corrections to the interference are large and similar in size to the corrections to both the signal and the background processes. At the same time, we observe that corrections to the interference change rapidly with the four-lepton invariant mass in the region around the ZZ production threshold. We also study the interference effects in $gg \to WW$ production where, due to technical limitations, we only consider contributions of massless loops. We find that the QCD corrections to the interference in this case are somewhat larger than those for either the signal or the background.Caola, FabrizioDowling, MatthewMelnikov, KirillRöntsch, RaoulTancredi, LorenzoTue, 17 May 2016 05:35:27 GMT15 May 2016arXiv:1605.04610https://cds.cern.ch/record/2153477['arXiv:1605.04610']arXiv:1605.04610Towards the compression of parton densities through machine learning algorithms
https://cds.cern.ch/record/2153473
One of the most fascinating challenges in the context of parton density function (PDF) is the determination of the best combined PDF uncertainty from individual PDF sets. Since 2014 multiple methodologies have been developed to achieve this goal. In this proceedings we first summarize the strategy adopted by the PDF4LHC15 recommendation and then, we discuss about a new approach to Monte Carlo PDF compression based on clustering through machine learning algorithms.Carrazza, StefanoLatorre, José ITue, 17 May 2016 05:35:26 GMT13 May 2016arXiv:1605.04345https://cds.cern.ch/record/2153473['arXiv:1605.04345']arXiv:1605.04345Cosmology and Supergravity
https://cds.cern.ch/record/2153435
Abdus Salam was a true master of 20th Century Theoretical Physics. Not only was he a pioneer of the Standard Model (for which he shared the Nobel Prize with S. Glashow and S.Weinberg), but he also (co)authored many other outstanding contributions to the field of Fundamental Interactions and their unification. In particular, he was a major contributor to the development of supersymmetric theories, where he also coined the word "Supersymmetry" (replacing the earlier "Supergauges" drawn from String Theory). He also introduced the basic concept of "Superspace" and the notion of "Goldstone Fermion"(Goldstino). These concepts proved instrumental for the exploration of the ultraviolet properties and for the study of spontaneously broken phases of super Yang-Mills theories and Supergravity. They continue to play a key role in current developments in Early-Universe Cosmology. In this contribution we review models of inflation based on Supergravity with spontaneously broken local supersymmetry, with emphasis on the role of nilpotent superfields to describe a de Sitter phase of our Universe.Ferrara, SKehagias, ASagnotti, ATue, 17 May 2016 05:34:06 GMT16 May 2016arXiv:1605.04791https://cds.cern.ch/record/2153435['arXiv:1605.04791']arXiv:1605.04791The ABC (in any D) of Logarithmic CFT
https://cds.cern.ch/record/2153252
Logarithmic conformal field theories have a vast range of applications, from critical percolation to systems with quenched disorder. In this paper we thoroughly examine the structure of these theories based on their symmetry properties. Our analysis is model-independent and holds for any spacetime dimension. Our results include a determination of the general form of correlation functions and conformal block decompositions, clearing the path for future bootstrap applications. Several examples are discussed in detail, including logarithmic generalized free fields, holographic models, self-avoiding random walks and critical percolation.Hogervorst, MatthijsPaulos, MiguelVichi, AlessandroMon, 16 May 2016 06:16:53 GMT12 May 2016arXiv:1605.03959https://cds.cern.ch/record/2153252['arXiv:1605.03959']arXiv:1605.03959First complete study of hadroproduction of a $\Upsilon$ meson associated with a prompt $J/\psi$
https://cds.cern.ch/record/2152159
We present the first complete study of $\Upsilon$ and prompt $J/\psi$ production from single-parton scattering, including the complete $\mathcal{O}(\alpha_S^6)$ color-singlet contribution, the $\mathcal{O}(\alpha_S^2\alpha^2)$ electroweak contribution, the complete non-relativistic S-wave and P-wave color-octet contribution as well as the feeddown contribution. Our study motivated by the recent evidence reported by D0 collaboration of prompt $J/\psi$ and $\Upsilon$ simultaneous production at the Tevatron. With our complete evaluation, we are able to refine the determination of the double parton scattering contribution made by D0. We find that the effective cross section characterizing the importance of double-parton scatterings is $\sigma_{\rm eff}\le 8.2$ mb at $68\%$ confidence level from D0 measurement.Shao, Hua-ShengZhang, Yu-JieThu, 12 May 2016 05:42:55 GMT10 May 2016arXiv:1605.03061https://cds.cern.ch/record/2152159['arXiv:1605.03061']arXiv:1605.03061Time-Sliced Perturbation Theory II: Baryon Acoustic Oscillations and Infrared Resummation
https://cds.cern.ch/record/2151429
We use time-sliced perturbation theory (TSPT) to give an accurate description of the infrared non-linear effects affecting the baryonic acoustic oscillations (BAO) present in the distribution of matter at very large scales. In TSPT this can be done via a systematic resummation that has a simple diagrammatic representation and does not involve uncontrollable approximations. We discuss the power counting rules and derive explicit expressions for the resummed matter power spectrum up to next-to leading order and the bispectrum at the leading order. The two-point correlation function agrees well with N-body data at BAO scales. The systematic approach also allows to reliably assess the shift of the baryon acoustic peak due to non-linear effects.Blas, DiegoGarny, MathiasIvanov, Mikhail MSibiryakov, SergeyTue, 10 May 2016 06:17:19 GMT07 May 2016arXiv:1605.02149https://cds.cern.ch/record/2151429['arXiv:1605.02149']arXiv:1605.02149Composite operators and form factors in N=4 SYM
https://cds.cern.ch/record/2150957
We construct the most general composite operators of N = 4 SYM in Lorentz harmonic chiral ($\approx$ twistor) superspace. The operators are built from the SYM supercurvature which is nonpolynomial in the chiral gauge prepotentials. We reconstruct the full nonchiral dependence of the supercurvature. We compute all tree-level MHV form factors via the LSZ redcution procedure with on-shell states made of the same supercurvature.Chicherin, DmitrySokatchev, EmeryFri, 06 May 2016 06:28:17 GMT04 May 2016arXiv:1605.01386https://cds.cern.ch/record/2150957['arXiv:1605.01386']arXiv:1605.01386Maximal Flavor Violation in Super-GUTs
https://cds.cern.ch/record/2150939
We consider supersymmetric grand unified theories with soft supersymmetry-breaking scalar masses $m_0$ specified above the GUT scale (super-GUTs) and patterns of Yukawa couplings motivated by upper limits on flavour-changing interactions beyond the Standard Model. If the scalar masses are smaller than the gaugino masses $m_{1/2}$, as is expected in no-scale models, the dominant effects of renormalization between the input scale and the GUT scale are generally expected to be those due to the gauge couplings, which are proportional to $m_{1/2}$ and generation-independent. In this case, the input scalar masses $m_0$ may violate flavour maximally, a scenario we call MaxFV, and there is no supersymmetric flavour problem. We illustrate this possibility within various specific super-GUT scenarios that are deformations of no-scale gravity.Ellis, JohnOlive, KeithVelasco-Sevilla, LilianaFri, 06 May 2016 06:27:03 GMT04 May 2016arXiv:1605.01398https://cds.cern.ch/record/2150939['arXiv:1605.01398']arXiv:1605.01398Parton Shower Uncertainties with Herwig 7: Benchmarks at Leading Order
https://cds.cern.ch/record/2150935
We perform a detailed study of the sources of perturbative uncertainty in parton shower predictions within the Herwig 7 event generator. We benchmark two rather different parton shower algorithms, based on angular-ordered and dipole-type evolution, against each other. We deliberately choose leading order plus parton shower as the benchmark setting to identify a controllable set of uncertainties. This will enable us to reliably assess improvements by higher-order contributions in a follow-up work.Bellm, JohannesNail, GraemePlätzer, SimonSchichtel, PeterSiódmok, AndrzejFri, 06 May 2016 06:26:59 GMT04 May 2016arXiv:1605.01338https://cds.cern.ch/record/2150935['arXiv:1605.01338']arXiv:1605.01338Heavy ions at the Future Circular Collider
https://cds.cern.ch/record/2150910
The Future Circular Collider (FCC) Study is aimed at assessing the physics potential and the technical feasibility of a new collider with centre-of-mass energies, in the hadron-hadron collision mode, seven times larger than the nominal LHC energies. Operating such machine with heavy ions is an option that is being considered in the accelerator design studies. It would provide, for example, Pb-Pb and p-Pb collisions at sqrt{s_NN} = 39 and 63 TeV, respectively, per nucleon-nucleon collision, with integrated luminosities above 30 nb^-1 per month for Pb-Pb. This is a report by the working group on heavy-ion physics of the FCC Study. First ideas on the physics opportunities with heavy ions at the FCC are presented, covering the physics of the Quark-Gluon Plasma, of gluon saturation, of photon-induced collisions, as well as connections with other fields of high-energy physics.Dainese, AWiedemann, U AArmesto, Nd'Enterria, DJowett, J MLansberg, J -PMilhano, J GSalgado, C ASchaumann, Mvan Leeuwen, MAlbacete, J LAndronic, AAntonioli, PApolinario, LBass, SBeraudo, ABilandzic, ABorsanyi, SBraun-Munzinger, PChen, ZMendez, L CunqueiroDenicol, G SEskola, K JFloerchinger, SFujii, HGiubellino, PGreiner, CGrosse-Oetringhaus, J FKo, C -MKotko, PKrajczar, KKutak, KLaine, MLiu, YLombardo, M PLuzum, MMarquet, CMasciocchi, SOkorokov, VPaquet, J -FPaukkunen, HPetreska, EPierog, TPloskon, MRatti, CRezaeian, A HRiegler, WRojo, JRoland, CRossi, ASalam, G PSapeta, SSchicker, RSchmidt, CStachel, JUphoff, Jvan Hameren, AWatanabe, KXiao, B -WYuan, FZaslavsky, DZhou, KZhuang, PFri, 06 May 2016 06:25:45 GMT04 May 2016arXiv:1605.01389https://cds.cern.ch/record/2150910['arXiv:1605.01389']arXiv:1605.01389$W_\infty$ Algebras, Hawking Radiation and Information Retention by Stringy Black Holes
https://cds.cern.ch/record/2150902
We have argued previously, based on the analysis of two-dimensional stringy black holes, that information in stringy versions of four-dimensional Schwarzschild black holes (whose singular regions are represented by appropriate Wess-Zumino-Witten models) is retained by quantum $W$-symmetries when the horizon area is not preserved due to Hawking radiation. It is key that the exactly-marginal conformal world-sheet operator representing a massless stringy particle interacting with the black hole requires a contribution from $W_\infty$ generators in its vertex function. The latter correspond to delocalised, non-propagating, string excitations that guarantee the transfer of information between the string black hole and external particles. When infalling matter crosses the horizon, these topological states are excited via a process: (Stringy black hole) + infalling matter $\rightarrow $ (Stringy black hole)$^\star$, where the black hole is viewed as a stringy state with a specific configuration of $W_\infty$ charges that are conserved. Hawking radiation is then the reverse process, with conservation of the $W_\infty$ charges retaining information. The Hawking radiation spectrum near the horizon of a Schwarzschild or Kerr black hole is specified by matrix elements of higher-order currents that form a phase-space $W_{1+\infty}$ algebra. We show that an appropriate gauging of this algebra preserves the horizon two-dimensional area classically, as expected because the latter is a conserved Noether charge.Ellis, JohnMavromatos, Nick ENanopoulos, Dimitri VFri, 06 May 2016 06:24:51 GMT05 May 2016arXiv:1605.01653https://cds.cern.ch/record/2150902['arXiv:1605.01653']arXiv:1605.01653Hunting for Dark Particles with Gravitational Waves
https://cds.cern.ch/record/2150796
The LIGO observation of gravitational waves from a binary black hole merger has begun a new era in fundamental physics. If new dark sector particles, be they bosons or fermions, can coalesce into exotic compact objects (ECOs) of astronomical size, then the first evidence for such objects, and their underlying microphysical description, may arise in gravitational wave observations. In this work we study how the macroscopic properties of ECOs are related to their microscopic properties, such as dark particle mass and couplings. We then demonstrate the smoking gun exotic signatures that would provide observational evidence for ECOs, and hence new particles, in terrestrial gravitational wave observatories. Finally, we discuss how gravitational waves can test a core concept in general relativity: Hawking's area theorem.Giudice, Gian FMcCullough, MatthewUrbano, AlfredoFri, 06 May 2016 06:22:49 GMT04 May 2016arXiv:1605.01209https://cds.cern.ch/record/2150796['arXiv:1605.01209']arXiv:1605.01209Non-Perturbative Quantum Geometry III
https://cds.cern.ch/record/2150470
The Nekrasov-Shatashvili limit of the refined topological string on toric Calabi-Yau manifolds and the resulting quantum geometry is studied from a non-perturbative perspective. The quantum differential and thus the quantum periods exhibit Stockes phenomena over the combined string coupling and quantized Kaehler moduli space. We outline that the underlying formalism of exact quantization is generally applicable to points in moduli space featuring massless hypermultiplets, leading to non-perturbative band splitting. Our prime example is local P1xP1 near a conifold point in moduli space. In particular, we will present numerical evidence that in a Stockes chamber of interest the string based quantum geometry reproduces the non-perturbative corrections for the Nekrasov-Shatashvili limit of 4d supersymmetric SU(2) gauge theory at strong coupling found in the previous part of this series. A preliminary discussion of local P2 near the conifold point in moduli space is also provided.Krefl, DanielWed, 04 May 2016 06:06:17 GMT30 Apr 2016arXiv:1605.00182https://cds.cern.ch/record/2150470['arXiv:1605.00182']arXiv:1605.00182The 750 GeV Diphoton Resonance in the MSSM
https://cds.cern.ch/record/2150458
We propose a simple interpretation of the 750 GeV diphoton resonance as hinted by the current 13 TeV LHC data, within the context of the Minimal Supersymmetric extension of the Standard Model (MSSM). In the CP-conserving limit of the theory, the resonance may be identified with the heavier CP-even $H$ boson of the MSSM, whose gluon-fusion production and decay into two photons are enhanced by loops of the lightest supersymmetric partner of the top quark $\tilde{t}_1$ when its mass $m_{\tilde{t}_1}$ happens to be near the $\tilde{t}^*_1\tilde{t}_1$ threshold, i.e.~for $m_{\tilde{t}_1} \sim \frac12 M_H$ and, to a lesser extent, by resonant contributions due to $\tilde{t}_1^* \tilde{t}_1$ bound states. The scenario requires a relatively low supersymmetry-breaking scale~$M_S\lsim 1$~TeV, but large values of the higgsino mass parameter, $\mu \gsim 3$ TeV that leads to a strong $H \tilde{t}_1 \tilde{t}_1$ coupling. Such parameters can accommodate the observed mass and standard-like couplings of the 125~GeV $h$ boson in the MSSM, while satisfying all other constraints from the LHC and dark matter searches. We briefly discuss further characteristic features of such a scenario that could serve as a smoking gun towards its experimental discovery.Djouadi, AbdelhakPilaftsis, ApostolosWed, 04 May 2016 06:05:46 GMT03 May 2016arXiv:1605.01040https://cds.cern.ch/record/2150458['arXiv:1605.01040']arXiv:1605.01040Interference Effects in the Decays of 750 GeV States into $\gamma \gamma$ and $t\bar{t}$
https://cds.cern.ch/record/2150403
We consider interference effects in the production via gluon fusion in LHC collisions at 13 TeV and decays into $\gamma \gamma$ and $t {\bar t}$ final states of the putative 750 GeV state(s) $\Phi$, assumed here to be scalar and/or pseudo scalar particle(s). We revisit previous calculations of the interferences between the heavy-fermion loop-induced $gg \to \Phi \to \gamma \gamma$ signal and the continuum $gg\to \gamma\gamma$ QCD background, which can alter the production rate as well as modify the line-shape and apparent mass. We find a modest enhancement by $\sim 20$% under favorable circumstances, for a large $\Phi$ width close to the experimental upper limit $\sim 45$ GeV. The effect of interference on the apparent scalar-pseudoscalar mass difference in a two-Higgs-doublet model is found to be also modest. An exploratory study indicates that similar effects are to be expected in the $gg \to \Phi \to Z \gamma$ channel. In this and other models with a large $\Phi$ total width, the dominant $\Phi$ decays are expected to be into $t \bar t$ final states. We therefore also study the effects of interference of the $gg\to \Phi \to t\bar t$ signal with the $gg\to t \bar t$ continuum QCD background and show that in the presence of standard fermions only in the $gg\to \Phi$ loops, it is destructive causing a dip in the $t \bar t$ mass distribution. Including additional vector-like quarks leads to a different picture as peaks followed by dips can then occur. We use the absence of such effects in ATLAS and CMS data to constrain models of the production and decays of the $\Phi$ state(s).Djouadi, AbdelhakEllis, JohnQuevillon, JérémieWed, 04 May 2016 06:04:25 GMT02 May 2016arXiv:1605.00542https://cds.cern.ch/record/2150403['arXiv:1605.00542']arXiv:1605.00542Quantum Field Theory of Interacting Dark Matter/Dark Energy: Dark Monodromies
https://cds.cern.ch/record/2150356
We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory. Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations.D'Amico, GuidoHamill, TeresaKaloper, NemanjaWed, 04 May 2016 06:02:49 GMT03 May 2016arXiv:1605.00996https://cds.cern.ch/record/2150356['arXiv:1605.00996']arXiv:1605.00996S-Channel Dark Matter Simplified Models and Unitarity
https://cds.cern.ch/record/2149185
The ultraviolet structure of $s$-channel mediator dark matter simplified models at hadron colliders is considered. In terms of commonly studied $s$-channel mediator simplified models it is argued that at arbitrarily high energies the perturbative description of dark matter production in high energy scattering at hadron colliders will break down in a number of cases. This is analogous to the well documented breakdown of an EFT description of dark matter collider production. With this in mind, to diagnose whether or not the use of simplified models at the LHC is valid, perturbative unitarity of the scattering amplitude in the processes relevant to LHC dark matter searches is studied. The results are as one would expect: at the LHC and future proton colliders the simplified model descriptions of dark matter production are in general valid. As a result of the general discussion, a simple new class of previously unconsidered `Fermiophobic Scalar' simplified models is proposed, in which a scalar mediator couples to electroweak vector bosons. The Fermiophobic simplified model is well motivated and exhibits interesting collider and direct detection phenomenology.Englert, ChristophMcCullough, MatthewSpannowsky, MichaelThu, 28 Apr 2016 06:03:12 GMT27 Apr 2016arXiv:1604.07975https://cds.cern.ch/record/2149185['arXiv:1604.07975']arXiv:1604.07975Theory Advances in BSM Physics
https://cds.cern.ch/record/2148845
Rather than attempting to summarise the full spectrum of recent advances in Beyond the Standard Model (BSM) theory, which are many, in this talk I will instead take the opportunity to focus on two frameworks related to the hierarchy problem currently receiving significant attention. They are the `Twin Higgs' and the `Relaxion'. I will summarise the basic underlying structure of these theories at a non-expert level and highlight some interesting phenomenological signatures or outstanding problems.McCullough, MatthewWed, 27 Apr 2016 05:44:12 GMT25 Apr 2016arXiv:1604.07184https://cds.cern.ch/record/2148845['arXiv:1604.07184']arXiv:1604.07184Telling the spin of the di-photon resonance
https://cds.cern.ch/record/2148817
We argue that the spin of the 750 GeV resonance can be determined at the 99.7% confidence level in the di-photon channel with as few as 10 fb$^{-1}$ of luminosity. This result is true if the resonance is produced by gluon fusion (independently of the selection cuts) while an appropriate choice of selection cuts is needed if quark production is sub-dominantly present--which is the case of the Kaluza-Klein gravitational excitation under the hypothesis of a spin-2 resonance. A proportionally larger luminosity is required if the model for the spin-2 resonance includes a dominant production by quarks or in the absence of an efficient separation of the signal from the background.Fabbrichesi, MarcoPinamonti, MicheleUrbano, AlfredoWed, 27 Apr 2016 05:41:34 GMT23 Apr 2016arXiv:1604.06948https://cds.cern.ch/record/2148817['arXiv:1604.06948']arXiv:1604.06948Charm in Deep-Inelastic Scattering
https://cds.cern.ch/record/2148652
We show how to extend systematically the FONLL scheme for inclusion of heavy quark mass effects in DIS to account for the possible effects of an intrinsic charm component in the nucleon. We show that when there is no intrinsic charm, FONLL is equivalent to S-ACOT to any order in perturbation theory, while when an intrinsic charm component is included FONLL is identical to ACOT, again to all orders in perturbation theory. We discuss in detail the inclusion of top and bottom quarks to construct a variable flavour number scheme, and give explicit expressions for the construction of the structure functions $F^c_2$, $F^c_L$ and $F^c_3$ to NNLO.Ball, Richard DBonvini, MarcoRottoli, LucaWed, 27 Apr 2016 05:38:59 GMT08 Oct 2015arXiv:1510.02491https://cds.cern.ch/record/2148652['arXiv:1510.02491']arXiv:1510.02491On the Validity of the Effective Field Theory Approach to SM Precision Tests
https://cds.cern.ch/record/2148162
We discuss the conditions for an effective field theory (EFT) to give an adequate low-energy description of an underlying physics beyond the Standard Model (SM). Starting from the EFT where the SM is extended by dimension-6 operators, experimental data can be used without further assumptions to measure (or set limits on) the EFT parameters. The interpretation of these results requires instead a set of broad assumptions (e.g. power counting rules) on the UV dynamics. This allows one to establish, in a bottom-up approach, the validity range of the EFT description, and to assess the error associated with the truncation of the EFT series. We give a practical prescription on how experimental results could be reported, so that they admit a maximally broad range of theoretical interpretations. Namely, the experimental constraints on dimension-6 operators should be reported as functions of the kinematic variables that set the relevant energy scale of the studied process. This is especially important for hadron collider experiments where collisions probe a wide range of energy scales.Contino, RobertoFalkowski, AdamGoertz, FlorianGrojean, ChristopheRiva, FrancescoSat, 23 Apr 2016 06:28:27 GMT21 Apr 2016arXiv:1604.06444https://cds.cern.ch/record/2148162['arXiv:1604.06444']arXiv:1604.06444The accuracy of QCD perturbation theory at high energies
https://cds.cern.ch/record/2148145
We discuss the determination of the strong coupling $\alpha_\mathrm{\overline{MS}}^{}(m_\mathrm{Z})$ or equivalently the QCD $\Lambda$-parameter. Its determination requires the use of perturbation theory in $\alpha_s(\mu)$ in some scheme, $s$, and at some energy scale $\mu$. The higher the scale $\mu$ the more accurate perturbation theory becomes, owing to asymptotic freedom. As one step in our computation of the $\Lambda$-parameter in three-flavor QCD, we perform lattice computations in a scheme which allows us to non-perturbatively reach very high energies, corresponding to $\alpha_s = 0.1$ and below. We find that perturbation theory is very accurate there, yielding a three percent error in the $\Lambda$-parameter, while data around $\alpha_s \approx 0.2$ is clearly insufficient to quote such a precision. It is important to realize that these findings are expected to be generic, as our scheme has advantageous properties regarding the applicability of perturbation theory.Brida, Mattia DallaFritzsch, PatrickKorzec, TomaszRamos, AlbertoSint, StefanSommer, RainerSat, 23 Apr 2016 06:28:18 GMT21 Apr 2016arXiv:1604.06193https://cds.cern.ch/record/2148145['arXiv:1604.06193']arXiv:1604.06193Digamma, what next?
https://cds.cern.ch/record/2148143
If the 750 GeV resonance in the diphoton channel is confirmed, what are the measurements necessary to infer the properties of the new particle and understand its nature? We address this question in the framework of a single new scalar particle, called digamma ($\digamma$). We describe it by an effective field theory, which allows us to obtain general and model-independent results, and to identify the most useful observables, whose relevance will remain also in model-by-model analyses. We derive full expressions for the leading-order processes and compute rates for higher-order decays, digamma production in association with jets, gauge or Higgs bosons, and digamma pair production. We illustrate how measurements of these higher-order processes can be used to extract couplings, quantum numbers, and properties of the new particle.Franceschini, RobertoGiudice, Gian FKamenik, Jernej FMcCullough, MatthewRiva, FrancescoStrumia, AlessandroTorre, RiccardoSat, 23 Apr 2016 06:27:49 GMT21 Apr 2016arXiv:1604.06446https://cds.cern.ch/record/2148143['arXiv:1604.06446']arXiv:1604.06446