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ZZ production at high transverse momenta beyond NLO QCD
https://cds.cern.ch/record/2011816
We study the production of the four-lepton final state $l^+ l^- l^+ l^-$, predominantly produced by a pair of electroweak Z bosons, ZZ. Using the LoopSim method, we merge NLO QCD results for ZZ and ZZ+jet and obtain approximate NNLO predictions for ZZ production. The exact gluon-fusion loop-squared contribution to the ZZ process is also included. On top of that, we add to our merged sample the gluon-fusion ZZ+jet contributions from the gluon-gluon channel, which is formally of N^3LO and provides approximate results at NLO for the gluon-fusion mechanism. The predictions are obtained with the VBFNLO package and include the leptonic decays of the Z bosons with all off-shell and spin-correlation effects, as well as virtual photon contributions. We compare our predictions with existing results for the total inclusive cross section at NNLO and find a very good agreement. Then, we present results for differential distributions for two experimental setups, one used in searches for anomalous triple gauge boson couplings, the other in Higgs analyses in the four charged-lepton final state channel. We find that the approximate NNLO corrections are large, reaching up to 20% at high transverse momentum of the Z boson or the leading lepton, and are not covered by the NLO scale uncertainties. Distributions of the four-lepton invariant mass are, however, stable with respect to QCD corrections at this order.Campanario, FranciscoRauch, MichaelSapeta, SebastianFri, 24 Apr 2015 05:48:09 GMT21 Apr 2015arXiv:1504.05588https://cds.cern.ch/record/2011816Luminosity goals for a 100-TeV pp collider
https://cds.cern.ch/record/2011810
We consider diverse examples of science goals that provide a framework to assess luminosity goals for a future 100-TeV proton-proton collider.Hinchliffe, IanKotwal, AshutoshMangano, Michelangelo LQuigg, ChrisWang, Lian-TaoFri, 24 Apr 2015 05:46:56 GMT23 Apr 2015arXiv:1504.06108https://cds.cern.ch/record/2011810The Higgs boson, Supersymmetry and Dark Matter: Relations and Perspectives
https://cds.cern.ch/record/2011082
The discovery of a light Higgs boson at the LHC opens a broad program of studies and measurements to understand the role of this particle in connection with New Physics and Cosmology. Supersymmetry is the best motivated and most thoroughly formulated and investigated model of New Physics which predicts a light Higgs boson and can explain dark matter. This paper discusses how the study of the Higgs boson connects with the search for supersymmetry and for dark matter at the LHC and at a future $e^+e^-$ collider and with dedicated underground dark matter experiments.Arbey, AlexandreBattaglia, MarcoMahmoudi, FarvahTue, 21 Apr 2015 05:55:02 GMT20 Apr 2015arXiv:1504.05091https://cds.cern.ch/record/2011082The Decay of the Standard Model Higgs after Inflation
https://cds.cern.ch/record/2010530
We study the non-perturbative dynamics of the Standard Model (SM) after inflation, in the regime where the SM is decoupled from (or weakly coupled to) the inflationary sector. We use classical lattice simulations in an expanding box in (3+1) dimensions, modeling the SM gauge interactions with both global and Abelian-Higgs analogue scenarios. We consider different post-inflationary expansion rates. During inflation, the Higgs forms a condensate, which starts oscillating soon after inflation ends. Via non-perturbative effects, the oscillations lead to a fast decay of the Higgs into the SM species, transferring most of the energy into $Z$ and $W^{\pm}$ bosons. All species are initially excited far away from equilibrium, but their interactions lead them into a stationary stage, with exact equipartition among the different energy components. From there on the system eventually reaches equilibrium. We have characterized in detail, in the different expansion histories considered, the evolution of the Higgs and of its dominant decay products, until equipartition is established.Figueroa, Daniel GGarcia-Bellido, JuanTorrenti, FranciscoMon, 20 Apr 2015 05:24:35 GMT17 Apr 2015arXiv:1504.04600https://cds.cern.ch/record/2010530A Theta lift representation for the Kawazumi-Zhang and Faltings invariants of genus-two Riemann surfaces
https://cds.cern.ch/record/2010408
The Kawazumi-Zhang invariant $\varphi$ for compact genus-two Riemann surfaces was recently shown to be a eigenmode of the Laplacian on the Siegel upper half-plane, away from the separating node. Using the known behavior of $\varphi$ in the non-separating degeneration limit, and subject to a suitable vanishing theorem, I show that $\varphi$ can be obtained by a Borcherds-type Theta lift from a specific weak Jacobi form of weight $-2$. This provides the complete Fourier-Jacobi expansion of $\varphi$ near the non-separating node, gives full control on the asymptotics of $\varphi$ in the various degeneration limits, and reveals a mock-type holomorphic Siegel modular form underlying $\varphi$. Using the relation between the Faltings invariant, the Kawazumi-Zhang invariant and the Igusa cusp form, a Theta lift representation for Faltings' invariant in genus two readily follows.Pioline, BorisSat, 18 Apr 2015 05:48:55 GMT16 Apr 2015arXiv:1504.04182https://cds.cern.ch/record/2010408Dirac Triplet Extension of the MSSM
https://cds.cern.ch/record/2009283
In this paper we explore extensions of the Minimal Supersymmetric Standard Model involving two $SU(2)_L$ triplet chiral superfields that share a superpotential Dirac mass yet only one of which couples to the Higgs fields. This choice is motivated by recent work using two singlet superfields with the same superpotential requirements. We find that, as in the singlet case, the Higgs mass in the triplet extension can easily be raised to $125\,\text{GeV}$ without introducing large fine-tuning. For triplets that carry hypercharge, the regions of least fine tuning are characterized by small contributions to the $\mathcal T$ parameter, and light stop squarks, $m_{\tilde t_1} \sim 300-450\,\text{GeV}$; the latter is a result of the $\tan\beta$ dependence of the triplet contribution to the Higgs mass. Despite such light stop masses, these models are viable provided the stop-electroweakino spectrum is sufficiently compressed.Alvarado, CDelgado, AMartin, AOstdiek, BThu, 16 Apr 2015 08:41:29 GMT14 Apr 2015arXiv:1504.03683https://cds.cern.ch/record/2009283Electroweak and QCD corrections to top-pair hadroproduction in association with heavy bosons
https://cds.cern.ch/record/2008999
We compute the contribution of order $\alpha_S^2\alpha^2$ to the cross section of a top-antitop pair in association with at least one heavy Standard Model boson -- $Z$, $W^\pm$, and Higgs -- by including all effects of QCD, QED, and weak origin and by working in the automated MadGraph5_aMC@NLO framework. This next-to-leading order contribution is then combined with that of order $\alpha_S^3\alpha$, and with the two dominant lowest-order ones, $\alpha_S^2\alpha$ and $\alpha_S\alpha^2$, to obtain phenomenological results relevant to a 8, 13, and 100~TeV $pp$ collider.Frixione, SHirschi, VPagani, DShao, H -SZaro, MWed, 15 Apr 2015 05:50:57 GMT14 Apr 2015arXiv:1504.03446https://cds.cern.ch/record/2008999Halo-Independent Direct Detection Analyses Without Mass Assumptions
https://cds.cern.ch/record/2008997
Results from direct detection experiments are typically interpreted by employing an assumption about the dark matter velocity distribution, with results presented in the $m_\chi-\sigma_n$ plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the $v_{min}-\tilde{g}$ plane, but these in turn require an assumption on the dark matter mass. Here we present an extension of these halo-independent methods for dark matter direct detection which does not require a fiducial choice of the dark matter mass. With a change of variables from $v_{min}$ to nuclear recoil momentum ($p_R$), the full halo-independent content of an experimental result for any dark matter mass can be condensed into a single plot as a function of a new halo integral variable, which we call $\tilde{h}(p_R)$. The entire family of conventional halo-independent $\tilde{g}(v_{min})$ plots for all DM masses are directly found from the single $\tilde{h}(p_R)$ plot through a simple rescaling of axes. By considering results in $\tilde{h}(p_R)$ space, one can determine if two experiments are inconsistent for all masses and all physically possible halos, or for what range of dark matter masses the results are inconsistent for all halos, without the necessity of multiple $\tilde{g}(v_{min})$ plots for different DM masses. We conduct a sample analysis comparing the CDMS II Si events to the null results from LUX, XENON10, and SuperCDMS using our method and discuss how the mass-independent limits can be strengthened by imposing the physically reasonable requirement of a finite halo escape velocity.Anderson, Adam JFox, Patrick JKahn, YonatanMcCullough, MatthewWed, 15 Apr 2015 05:50:56 GMT13 Apr 2015arXiv:1504.03333https://cds.cern.ch/record/2008997The Physics Landscape after the Higgs Discovery at the LHC
https://cds.cern.ch/record/2008936
What is the Higgs boson telling us? What else is there, maybe supersymmetry and/or dark matter? How do we find it? These are now the big questions in collider physics that I discuss in this talk, from a personal point of view.Ellis, JohnWed, 15 Apr 2015 05:47:15 GMT14 Apr 2015arXiv:1504.03654https://cds.cern.ch/record/2008936The pMSSM10 after LHC Run 1
https://cds.cern.ch/record/2008859
We present a frequentist analysis of the parameter space of the pMSSM10, in which the following 10 soft SUSY-breaking parameters are specified independently at the mean scalar top mass scale Msusy = Sqrt[M_stop1 M_stop2]: the gaugino masses M_{1,2,3}, the 1st-and 2nd-generation squark masses M_squ1 = M_squ2, the third-generation squark mass M_squ3, a common slepton mass M_slep and a common trilinear mixing parameter A, the Higgs mixing parameter mu, the pseudoscalar Higgs mass M_A and tan beta. We use the MultiNest sampling algorithm with 1.2 x 10^9 points to sample the pMSSM10 parameter space. A dedicated study shows that the sensitivities to strongly-interacting SUSY masses of ATLAS and CMS searches for jets, leptons + MET signals depend only weakly on many of the other pMSSM10 parameters. With the aid of the Atom and Scorpion codes, we also implement the LHC searches for EW-interacting sparticles and light stops, so as to confront the pMSSM10 parameter space with all relevant SUSY searches. In addition, our analysis includes Higgs mass and rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the measurements B-physics observables, EW precision observables, the CDM density and searches for spin-independent DM scattering. We show that the pMSSM10 is able to provide a SUSY interpretation of (g-2)_mu, unlike the CMSSM, NUHM1 and NUHM2. As a result, we find (omitting Higgs rates) that the minimum chi^2/dof = 20.5/18 in the pMSSM10, corresponding to a chi^2 probability of 30.8 %, to be compared with chi^2/dof = 32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1) (NUHM2). We display 1-dimensional likelihood functions for SUSY masses, and show that they may be significantly lighter in the pMSSM10 than in the CMSSM, NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e+e- colliders and direct detection experiments.de Vries, K JBagnaschi, E ABuchmueller, OCavanaugh, RCitron, MDe Roeck, ADolan, M JEllis, J RFlaecher, HHeinemeyer, SIsidori, GMalik, SMarrouche, JSantos, D MartinezOlive, K ASakurai, KWeiglein, GWed, 15 Apr 2015 05:47:04 GMT13 Apr 2015arXiv:1504.03260https://cds.cern.ch/record/2008859Dark Matter from the Supersymmetric Custodial Triplet Model
https://cds.cern.ch/record/2008528
The Supersymmetric Custodial Triplet Model (SCTM) adds to the particle content of the MSSM three $SU(2)_L$ triplet chiral superfields with hypercharge $Y=(0,\pm1)$. At the superpotential level the model respects a global $SU(2)_L \otimes SU(2)_R$ symmetry only broken by the Yukawa interactions. The pattern of vacuum expectation values of the neutral doublet and triplet scalar fields depends on the symmetry pattern of the Higgs soft breaking masses. We study the cases where this symmetry is maintained in the Higgs sector, and when it is broken only by the two doublets attaining different vacuum expectation values. In the former case, the symmetry is spontaneously broken down to the vectorial subgroup $SU(2)_V$ and the $\rho$ parameter is protected by the custodial symmetry. However in both situations the $\rho$ parameter is protected at tree level, allowing for light triplet scalars with large vacuum expectation values. We find that over a large range of parameter space, a light neutralino can supply the correct relic abundance of dark matter either through resonant s-channel triplet scalar funnels or well tempering of the Bino with the triplet fermions. Direct detection experiments have trouble probing these model points because the custodial symmetry suppresses the coupling of the neutralino and the $Z$ and a small Higgsino component of the neutralino suppresses the coupling with the Higgs. Likewise the annihilation cross sections for indirect detection lie below the Fermi-LAT upper bounds for the different channels.Delgado, AntonioGarcia-Pepin, MateoOstdiek, BryanQuiros, MarianoMon, 13 Apr 2015 05:43:18 GMT09 Apr 2015arXiv:1504.02486https://cds.cern.ch/record/2008528Combining LEP and LHC to bound the Higgs Width
https://cds.cern.ch/record/2008341
The correlation of on- and off-shell Higgs boson production at the LHC in $gg \to h^* \to ZZ$ to bound the Higgs width, under specific model-dependent assumptions, has recently received a lot of attention. As off-shell cross section measurements in this channel suffer from a small signal yield, large backgrounds, and theoretical uncertainties, we propose an alternative complementary constraint which is only possible through the combination of LEP and LHC measurements. Previous precision electroweak measurements at LEP allow for the determination of indirect constraints on Higgs couplings to vector bosons by considering one-loop processes involving virtual Higgs exchange. As the Higgs is off-shell in these diagrams we venture that LEP can be interpreted as an off-shell `Higgs Factory'. By combining these LEP constraints with current LHC 8 TeV Higgs measurements a stronger limit on the Higgs width can be achieved than with LHC data alone for models with rescaled Higgs couplings. Looking to the future, avoiding ambiguities arising due to new physics modifications of the $hGG$ coupling, a theoretically more robust constraint can be achieved by correlating LEP measurements with WBF Higgs production followed by Higgs decays to $WW$ and $ZZ$. This method for indirectly constraining the Higgs width is very effective for specific BSM scenarios and is highly complementary to other proposed methods. The limits we obtain particularly highlight the power of a concrete LEP+LHC combination, not only limited to Higgs width measurements.Englert, ChristophMcCullough, MatthewSpannowsky, MichaelSat, 11 Apr 2015 05:35:29 GMT09 Apr 2015arXiv:1504.02458https://cds.cern.ch/record/2008341Comparing EFT and Exact One-Loop Analyses of Non-Degenerate Stops
https://cds.cern.ch/record/2008324
We develop a universal approach to the one-loop effective field theory (EFT) using the Covariant Derivative Expansion (CDE) method. We generalise previous results to include broader classes of UV models, showing how expressions previously obtained assuming degenerate heavy-particle masses can be extended to non-degenerate cases. We apply our method to the general MSSM with non-degenerate stop squarks, illustrating our approach with calculations of the coefficients of dimension-6 operators contributing to the $hgg$ and $h\gamma\gamma$ couplings, and comparing with exact calculations of one-loop Feynman diagrams. We then use present and projected future sensitivities to these operator coefficients to obtain present and possible future indirect constraints on stop masses. The current sensitivity is already comparable to that of direct LHC searches, and future FCC-ee measurements could be sensitive to stop masses above a TeV. The universality of our one-loop EFT approach facilitates extending these constraints to a broader class of UV models.Drozd, AleksandraEllis, JohnQuevillon, JeremieYou, TevongSat, 11 Apr 2015 05:34:56 GMT09 Apr 2015arXiv:1504.02409https://cds.cern.ch/record/2008324Physics at the e+ e- Linear Collider
https://cds.cern.ch/record/2007590
A comprehensive review of physics at an e+e- Linear Collider in the energy range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC results, experiments from low energy as well as astroparticle physics.The report focuses in particular on Higgs boson, Top quark and electroweak precision physics, but also discusses several models of beyond the Standard Model physics such as Supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analyzed as well.Moortgat-Pick, GBaer, HBattaglia, MBelanger, GFujii, KKalinowski, JHeinemeyer, SKiyo, YOlive, KSimon, FUwer, PWackeroth, DZerwas, P MArbey, AAsano, MBechtle, PBharucha, ABrau, JBrummer, FChoi, S YDenner, ADesch, KDittmaier, SEllis, JEllwanger, UEnglert, CFreitas, AGinzburg, IGodfrey, SGreiner, NGrojean, CGrunewald, MHeisig, JHocker, AKanemura, SKawagoe, KKogler, RKrawczyk, MKronfeld, A SKroseberg, JLiebler, SList, JMahmoudi, FMambrini, YMatsumoto, SMnich, JMonig, KMuhlleitner, M MPoschl, RPorod, WPorto, SRolbiecki, KSchlatter, DSchmitt, MSerpico, PStanitzki, MStål, OStefaniak, TStockinger, DWagner, AWeiglein, GWilson, G WZeune, LMoortgat, FXella, SThu, 09 Apr 2015 05:29:01 GMT07 Apr 2015arXiv:1504.01726https://cds.cern.ch/record/2007590Electroweak Symmetry Breaking without the $\mu^2$ Term
https://cds.cern.ch/record/2005983
We demonstrate that from a low energy perspective a viable electroweak symmetry breaking can be achieved without the (negative sign) $\mu^2$ mass term in the Higgs potential, thereby avoiding completely the appearance of relevant operators. We show that such a setup is self consistent and not ruled out by Higgs physics. In particular, we point out that it is the lightness of the Higgs boson that allows for the electroweak symmetry to be broken dynamically via operators of $D\geq 4$, consistent with the power expansion. Beyond that, we entertain how this scenario might even be preferred phenomenologically compared to the ordinary mechanism of electroweak symmetry breaking, as realized in the Standard Model, and argue that it can be fully tested at the LHC. In an appendix, we classify UV completions that could lead to such a setup, considering also the option of generating all scales dynamically.Goertz, FlorianThu, 02 Apr 2015 06:38:16 GMT01 Apr 2015arXiv:1504.00355https://cds.cern.ch/record/2005983Two-loop helicity amplitudes for the production of two off-shell electroweak bosons in gluon fusion
https://cds.cern.ch/record/2005540
We compute the part of the two-loop virtual amplitude for the process $gg \to V_1 V_2 \to (l_1 \bar l'_{1}) (l_2 \bar l'_2)$, where $V_{1,2}$ are arbitrary electroweak gauge bosons, that receives contributions from loops of massless quarks. Invariant masses of electroweak bosons are allowed to be different from each other. Our result provides an important ingredient for improving the description of gluon fusion contribution to the production of four-lepton final states at the LHC.Caola, FabrizioHenn, Johannes MMelnikov, KirillSmirnov, Alexander VSmirnov, Vladimir AWed, 01 Apr 2015 05:57:27 GMT30 Mar 2015arXiv:1503.08759https://cds.cern.ch/record/2005540Effective operators in SUSY, superfield constraints and searches for a UV completion
https://cds.cern.ch/record/2005527
We discuss the role of a class of higher dimensional operators in 4D N=1 supersymmetric effective theories. The Lagrangian in such theories is an expansion in momenta below the scale of "new physics" ($\Lambda$) and contains the effective operators generated by integrating out the "heavy states" above $\Lambda$ present in the UV complete theory. We go beyond the "traditional" leading order in this momentum expansion (in $\partial/\Lambda$). Keeping manifest supersymmetry and using superfield {\it constraints} we show that the corresponding higher dimensional (derivative) operators in the sectors of chiral, linear and vector superfields of a Lagrangian can be "unfolded" into second-order operators. The "unfolded" formulation has only polynomial interactions and additional massive superfields, some of which are ghost-like if the effective operators were {\it quadratic} in fields. Using this formulation, the UV theory emerges naturally and fixes the (otherwise unknown) coefficient and sign of the initial (higher derivative) operators. Integrating the massive fields of the "unfolded" formulation generates an effective theory with only polynomial effective interactions relevant for phenomenology. We also provide several examples of "unfolding" of theories with higher derivative {\it interactions} in the gauge or matter sectors that are actually ghost-free. We then illustrate how our method can be applied even when including {\it all orders} in the momentum expansion, by using an infinite set of superfield constraints and an iterative procedure, with similar results.Dudas, EGhilencea, D MWed, 01 Apr 2015 05:57:25 GMT28 Mar 2015arXiv:1503.08319https://cds.cern.ch/record/2005527Phenomenological Aspects of No-Scale Inflation Models
https://cds.cern.ch/record/2005413
We discuss phenomenological aspects of no-scale supergravity inflationary models motivated by compactified string models, in which the inflaton may be identified either as a K\"ahler modulus or an untwisted matter field, focusing on models that make predictions for the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$ that are similar to the Starobinsky model. We discuss possible patterns of soft supersymmetry breaking, exhibiting examples of the pure no-scale type $m_0 = B_0 = A_0 = 0$, of the CMSSM type with universal $A_0$ and $m_0 \ne 0$ at a high scale, and of the mSUGRA type with $A_0 = B_0 + m_0$ boundary conditions at the high input scale. These may be combined with a non-trivial gauge kinetic function that generates gaugino masses $m_{1/2} \ne 0$, or one may have a pure gravity mediation scenario where trilinear terms and gaugino masses are generated through anomalies. We also discuss inflaton decays and reheating, showing possible decay channels for the inflaton when it is either an untwisted matter field or a K\"ahler modulus. Reheating is very efficient if a matter field inflaton is directly coupled to MSSM fields, and both candidates lead to sufficient reheating in the presence of a non-trivial gauge kinetic function.Ellis, JohnGarcia, Marcos A GNanopoulos, Dimitri VOlive, Keith AWed, 01 Apr 2015 05:52:20 GMT30 Mar 2015arXiv:1503.08867https://cds.cern.ch/record/2005413Non-linear curvature inhomogeneities and backreaction for relativistic viscous fluids
https://cds.cern.ch/record/2005386
The non-perturbative curvature inhomogeneities induced by relativistic viscous fluids are not conserved in the large-scale limit. However when the bulk viscosity is a function of the total energy density of the plasma (or of the trace of the extrinsic curvature) the relevant evolution equations develop a further symmetry preventing the non-linear growth of curvature perturbations. In this situation the fully inhomogeneous evolution can be solved to leading order in the gradient expansion. Over large-scales both the acceleration and the curvature inhomogeneities are determined by the bulk viscosity coefficients. Conversely the shear viscosity does not affect the evolution of the curvature and does not produce any acceleration. The curvature modes analyzed here do not depend on the choice of time hypersurfaces and are invariant for infinitesimal coordinate transformations in the perturbative regime.Giovannini, MassimoWed, 01 Apr 2015 05:52:14 GMT30 Mar 2015arXiv:1503.08739https://cds.cern.ch/record/2005386QCD phase diagram from the lattice at strong coupling
https://cds.cern.ch/record/2004991
The phase diagram of lattice QCD in the strong coupling limit can be measured in the full $\mu$-$T$ plane, also in the chiral limit. In particular, the phase diagram in the chiral limit features a tricritical point at some $(\mu_c,T_c)$. This point may be related to the critical end point expected in the QCD phase diagram. We discuss the gauge corrections to the phase diagram at strong coupling and compare our findings with various possible scenarios in continuum QCD. We comment on the possibility that the tricritical point at strong coupling is connected to the tricritical point in the continuum, massless QCD.de Forcrand, PhilippePhilipsen, OweUnger, WolfgangMon, 30 Mar 2015 05:41:16 GMT27 Mar 2015arXiv:1503.08140https://cds.cern.ch/record/2004991Semiclassical S-matrix for black holes
https://cds.cern.ch/record/2004546
We propose a semiclassical method to calculate S-matrix elements for two-stage gravitational transitions involving matter collapse into a black hole and evaporation of the latter. The method consistently incorporates back-reaction of the collapsing and emitted quanta on the metric. We illustrate the method in several toy models describing spherical self-gravitating shells in asymptotically flat and AdS space-times. We find that electrically neutral shells reflect via the above collapse-evaporation process with probability exp(-B), where B is the Bekenstein-Hawking entropy of the intermediate black hole. This is consistent with interpretation of exp(B) as the number of black hole states. The same expression for the probability is obtained in the case of charged shells if one takes into account instability of the Cauchy horizon of the intermediate Reissner-Nordstrom black hole. Our semiclassical method opens a new systematic approach to the information paradox.Bezrukov, FedorLevkov, DmitrySibiryakov, SergeyFri, 27 Mar 2015 06:41:15 GMT24 Mar 2015arXiv:1503.07181https://cds.cern.ch/record/2004546Cross-Order Integral Relations from Maximal Cuts
https://cds.cern.ch/record/2003992
We study the ABDK relation using maximal cuts of one- and two-loop integrals with up to five external legs. We show how to find a special combination of integrals that allows the relation to exist, and how to reconstruct the terms with one-loop integrals squared. The reconstruction relies on the observation that integrals across different loop orders can have support on the same generalized unitarity cuts and can share global poles. We discuss the appearance of nonhomologous integration contours in multivariate residues. Their origin can be understood in simple terms, and their existence enables us to distinguish contributions from different integrals. Our analysis suggests that maximal and near-maximal cuts can be used to infer the existence of integral identities more generally.Johansson, HenrikKosower, David ALarsen, Kasper JSogaard, MadsWed, 25 Mar 2015 17:35:58 GMT23 Mar 2015arXiv:1503.06711https://cds.cern.ch/record/2003992Gluino Coannihilation Revisited
https://cds.cern.ch/record/2003926
Some variants of the MSSM feature a strip in parameter space where the lightest neutralino is identified as the lightest supersymmetric particle (LSP), the gluino is the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with the LSP, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP. We calculate the relic density along this gluino coannihilation strip in the MSSM, including the effects of gluino-gluino bound states and initial-state Sommerfeld enhancement, and taking into account the decoupling of the gluino and LSP densities that occurs for large values of the squark mass. We find that bound-state effects can increase the maximum LSP mass for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ~ 50% if the squark to gluino mass ratio is 1.1, and that the LSP may weigh up to ~ 8 TeV for a wide range of the squark to gluino mass ratio \lesssim 100.Ellis, JohnLuo, FengOlive, Keith AWed, 25 Mar 2015 17:31:20 GMT24 Mar 2015arXiv:1503.07142https://cds.cern.ch/record/2003926Matching NLO QCD with parton shower in Monte Carlo scheme - the KrkNLO method
https://cds.cern.ch/record/2003785
A new method of including the complete NLO QCD corrections to hard processes in the LO parton-shower Monte Carlo (PSMC) is presented. This method, called KrkNLO, requires the use of parton distribution functions in a dedicated Monte Carlo factorization scheme, which is also discussed in this paper. In the future, it may simplify introduction of the NNLO corrections to hard processes and the NLO corrections to PSMC. Details of the method and numerical examples of its practical implementation, as well as comparisons with other calculations, such as MCFM, MC@NLO, POWHEG, for single $Z/\gamma^*$-boson production at the LHC, are presented.Jadach, SPlaczek, WSapeta, SSiodmok, ASkrzypek, MWed, 25 Mar 2015 17:10:39 GMT23 Mar 2015arXiv:1503.06849https://cds.cern.ch/record/2003785Higgs boson gluon-fusion production in N3LO QCD
https://cds.cern.ch/record/2003776
We present the cross-section for the production of a Higgs boson at hadron-colliders at next-to- next-to-next-to-leading order (N3LO) in perturbative QCD. The calculation is based on a method to perform a series expansion of the partonic cross-section around the threshold limit to an arbitrary order. We perform this expansion to sufficiently high order to obtain the value of the hadronic cross at N3LO in the large top-mass limit. For renormalisation and factorisation scales equal to half the Higgs mass, the N3LO corrections are of the order of +2.2%. The total scale variation at N3LO is 3%, reducing the uncertainty due to missing higher order QCD corrections by a factor of three.Anastasiou, CharalamposDuhr, ClaudeDulat, FalkoHerzog, FranzMistlberger, BernhardWed, 25 Mar 2015 17:10:36 GMT20 Mar 2015arXiv:1503.06056https://cds.cern.ch/record/2003776