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Relaxing the Electroweak Scale: the Role of Broken dS Symmetry
https://cds.cern.ch/record/2039436
Recently, a novel mechanism to address the hierarchy problem has been proposed [1], where the hierarchy between weak scale physics and any putative `cutoff' $M$ is translated into a parametrically large field excursion for the so-called relaxion field, driving the Higgs mass to values much less than $M$ through cosmological dynamics. In its simplest incarnation, the relaxion mechanism requires nothing beyond the standard model other than an axion (the relaxion field) and an inflaton. In this note, we critically re-examine the requirements for successfully realizing the relaxion mechanism and point out that parametrically larger field excursions can be obtained for a given number of e-folds by simply requiring that the background break exact de Sitter invariance. We discuss several corollaries of this observation, including the interplay between the upper bound on the scale $M$ and the order parameter $\epsilon$ associated with the breaking of dS symmetry, and the possibility that the relaxion could play the role of a curvaton. We find that a successful realization of the mechanism is possible with as few as $\mathcal O (10^3)$ e-foldings, albeit with a reduced cutoff $M \sim 10^6$ GeV for a dark QCD axion and outline a minimal scenario that can be made consistent with CMB observations.Patil, Subodh PSchwaller, PedroFri, 31 Jul 2015 05:35:46 GMT30 Jul 2015arXiv:1507.08649https://cds.cern.ch/record/2039436Global Parton Distributions for the LHC Run II
https://cds.cern.ch/record/2038936
We review the next generation global PDF sets: NNPDF3.0, MMHT14 and CT14. We describe the global datasets, particularly the new data from LHC Run 1, recent developments in QCD theory and PDF methodology, improvements in combination and delivery, and future prospects for parton determination at Run 2.Ball, Richard DThu, 30 Jul 2015 05:53:28 GMT28 Jul 2015arXiv:1507.07891https://cds.cern.ch/record/2038936A perturbed lepton-specific two-Higgs-doublet model facing experimental hints for physics beyond the Standard Model
https://cds.cern.ch/record/2038929
The BaBar, Belle, and LHCb collaborations have reported evidence for new physics in $B\to D\tau\nu$ and $B\to D^*\tau\nu$ of approximately $3.8\sigma$. There is also the long lasting discrepancy of about $3\sigma$ in the anomalous magnetic moment of the muon, and the branching ratio for $\tau\to\mu\nu\nu$ is $1.8\sigma$ ($2.4\sigma$) above the Standard Model expectation using the HFAG (PDG) values. Furthermore, CMS found hints for a non-zero decay rate of $h\to\mu\tau$. Interestingly, all these observations can be explained by introducing new scalars. In this article we consider these processes within a lepton-specific two-Higgs doublet model (i.e. of type X) with additional non-standard Yukawa couplings. It is found that one can accommodate $\tau\to\mu\nu\nu$ with modified Higgs--$\tau$ couplings. The anomalous magnetic moment of the muon can be explained if the additional neutral CP-even Higgs $H$ is light (below 100 GeV). Also $R(D)$ and $R(D^*)$ can be easily explained by additional $t$--$c$--Higgs couplings. Combining these $t$--$c$ couplings with a light $H$ the decay rate for $t\to H c$ can be in a testable range for the LHC. Effects in $h\to\mu\tau$ are also possible, but in this case a simultaneous explanation of the anomalous magnetic moment of the muon is difficult due to the unavoidable $\tau\to\mu\gamma$ decay.Crivellin, AndreasHeeck, JulianStoffer, PeterThu, 30 Jul 2015 05:53:23 GMT27 Jul 2015arXiv:1507.07567https://cds.cern.ch/record/2038929Lorentz violation in gravity
https://cds.cern.ch/record/2038911
The study of gravitational theories without Lorentz invariance plays an important role to understand different aspects of gravitation. In this short contribution we will describe the construction, main advantages and some phenomenological considerations associated with the presence of a preferred time direction.Blas, DiegoThu, 30 Jul 2015 05:52:49 GMT28 Jul 2015arXiv:1507.07687https://cds.cern.ch/record/2038911Lepton Flavour Violating top decays at the LHC
https://cds.cern.ch/record/2038308
We consider lepton flavour violating decays of the top quark, mediated by four-fermion operators. We compile constraints on a complete set of SU(3)*U(1)-invariant operators, arising from their loop contributions to rare decays and from HERA's single top search. The bounds on e-mu flavour change are more restrictive than l-tau; nonetheless the top could decay to a jet $+ e \bar{\mu}$ with a branching ratio of order $10^{-3}$. We estimate that the currently available LHC data (20 inverse-fb at 8 TeV) could be sensitive to $BR(t \to e \bar{\mu}$+ jet) $ \sim 6\times 10^{-5}$, and extrapolate that 100 inverse-fb at 13 TeV could reach a sensitivity of $ \sim 1 \times 10^{-5}$.Davidson, SachaMangano, Michelangelo LPerries, StephaneSordini, ViolaTue, 28 Jul 2015 09:24:16 GMT25 Jul 2015arXiv:1507.07163https://cds.cern.ch/record/2038308Heavy Vector Partners of the Light Composite Higgs
https://cds.cern.ch/record/2038290
If the Higgs boson $H(125)$ is a composite due to new strong interactions at high energy, it has spin-one partners, $\rho_H$ and $a_H$, analogous to the $\rho$ and $a_1$ mesons of QCD. These bosons are heavy, their mass determined by the strong interaction scale. The strongly interacting particles light enough for $\rho_H$ and $a_H$ to decay to are the longitudinal weak bosons $V_L = W_L,\, Z_L$ and the Higgs boson $H$. These decay signatures are consistent with resonant diboson excesses recently reported near 2 TeV by ATLAS and CMS. We calculate $\sigma\times BR(\rho_H \to VV) =$ few fb and $\sigma\times BR(a_H \to VH) =$ 0.5--1 fb at $\sqrt{s} =$ 8 TeV, increasing by a factor of 5--7 at 13 TeV. Other tests of the hypothesis of the strong-interaction nature of the diboson resonances are suggested.Lane, KennethPrichett, LukasTue, 28 Jul 2015 09:21:13 GMT25 Jul 2015arXiv:1507.07102https://cds.cern.ch/record/2038290Large scale structure from viscous dark matter
https://cds.cern.ch/record/2037741
Cosmological perturbations of sufficiently long wavelength admit a fluid dynamic description. We consider modes with wavevectors below a scale $k_m$ for which the dynamics is only mildly non-linear. The leading effect of modes above that scale can be accounted for by effective non-equilibrium viscosity and pressure terms. For mildly non-linear scales, these mainly arise from momentum transport within the ideal and cold but inhomogeneous fluid, while momentum transport due to more microscopic degrees of freedom is suppressed. As a consequence, concrete expressions with no free parameters, except the matching scale $k_m$, can be derived from matching evolution equations to standard cosmological perturbation theory. Two-loop calculations of the matter power spectrum in the viscous theory lead to excellent agreement with $N$-body simulations up to scales $k=0.2 \, h/$Mpc. The convergence properties in the ultraviolet are better than for standard perturbation theory and the results are robust with respect to variations of the matching scale.Blas, DiegoFloerchinger, StefanGarny, MathiasTetradis, NikolaosWiedemann, Urs AchimMon, 27 Jul 2015 05:26:24 GMT23 Jul 2015arXiv:1507.06665https://cds.cern.ch/record/2037741Quark flavour observables in the Littlest Higgs model with T-parity after LHC Run 1
https://cds.cern.ch/record/2037504
The Littlest Higgs Model with T-parity (LHT) belongs to the simplest new physics scenarios with new sources of flavour and CP violation. We present a new analysis of quark observables in the LHT model in view of the oncoming flavour precision era. We use all available information on the CKM parameters, lattice QCD input and experimental data on quark flavour observables and corresponding theoretical calculations, taking into account new lower bounds on the symmetry breaking scale and the mirror quark masses from the LHC. We investigate by how much the branching ratios for a number of rare $K$ and $B$ decays are still allowed to depart from their SM values. This includes $K^+\to\pi^+\nu\bar\nu$, $K_L\to\pi^0\nu\bar\nu$, $K_L\to \mu^+\mu^-$, $\epsilon'/\epsilon$, $B\to X_s\gamma$, $B_{s,d}\to\mu^+\mu^-$, $B\to K^{(*)}\ell^+\ell^-$, $B\to K^{(*)}\nu\bar\nu$. Taking into account the constraints from $\Delta F=2$ processes, significant departures from the SM predictions for $K^+\to\pi^+\nu\bar\nu$ and $K_L\to\pi^0\nu\bar\nu$ are possible while the effects in $B$ decays are much smaller. In particular, the LHT model favours $\mathcal{B}(B_{s}\to\mu^+\mu^-) \ge \mathcal{B}(B_{s}\to\mu^+\mu^-)_{\rm SM}$, which is not supported by the data, and the present anomalies in $B\to K^{(*)}\ell^+\ell^-$ decays cannot be explained in this model. With the recent lattice and large $N$ input the imposition of the $\epsilon'/\epsilon$ constraint implies a significant suppression of the branching ratio for $K_L\to\pi^0\nu\bar\nu$ with respect to its SM value while allowing only for small modifications for $K^+\to\pi^+\nu\bar\nu$. Finally, we investigate how the LHT physics could be distinguished from other models by means of indirect measurements and discuss the consequences for quark flavour observables of not finding any LHT state in the coming years.Blanke, MonikaBuras, Andrzej JRecksiegel, StefanFri, 24 Jul 2015 12:53:35 GMT22 Jul 2015arXiv:1507.06316https://cds.cern.ch/record/2037504Gluon PDF constraints from the ratio of forward heavy quark production at the LHC at $\sqrt{S}$ = 7 and 13 TeV
https://cds.cern.ch/record/2036936
We discuss production of charm and bottom quarks at forward rapidity in pp collisions at the LHC, updating the QCD predictions for the run at $\sqrt{S}$ = 13 TeV. We show that, while the absolute rates suffer from large theoretical systematics, dominated by scale uncertainties, the increase relative to the rates precisely measured at 7 TeV can be predicted with an accuracy of a few percent, sufficient to highlight the sensitivity to the gluon distribution function.Cacciari, MatteoMangano, Michelangelo LNason, PaoloThu, 23 Jul 2015 06:24:46 GMT22 Jul 2015arXiv:1507.06197https://cds.cern.ch/record/2036936Evanescent Effects Can Alter Ultraviolet Divergences in Quantum Gravity without Physical Consequences
https://cds.cern.ch/record/2036928
Evanescent operators such as the Gauss-Bonnet term have vanishing perturbative matrix elements in exactly D=4 dimensions. Similarly, evanescent fields do not propagate in D=4; a three-form field is in this class, since it is dual to a cosmological-constant contribution. In this Letter, we show that evanescent operators and fields modify the leading ultraviolet divergence in pure gravity. To analyze the divergence, we compute the two-loop identical-helicity four-graviton amplitude and determine the coefficient of the associated (non-evanescent) R^3 counterterm studied long ago by Goroff and Sagnotti. We compare two pairs of theories that are dual in D=4: gravity coupled to nothing or to three-form matter, and gravity coupled to zero-form or to two-form matter. Duff and van Nieuwenhuizen showed that, curiously, the one-loop conformal anomaly --- the coefficient of the Gauss-Bonnet operator --- changes under p-form duality transformations. We concur, and also find that the leading R^3 divergence changes under duality transformations. Nevertheless, in both cases the physical renormalized two-loop identical-helicity four-graviton amplitude can be chosen to respect duality. In particular, its renormalization-scale dependence is unaltered.Bern, ZviCheung, CliffordChi, Huan-HangDavies, ScottDixon, LanceNohle, JoshThu, 23 Jul 2015 06:24:12 GMT22 Jul 2015arXiv:1507.06118https://cds.cern.ch/record/2036928The $(2,0)$ superconformal bootstrap
https://cds.cern.ch/record/2036531
We develop the conformal bootstrap program for six-dimensional conformal field theories with $(2,0)$ supersymmetry, focusing on the universal four-point function of stress tensor multiplets. We review the solution of the superconformal Ward identities and describe the superconformal block decomposition of this correlator. We apply numerical bootstrap techniques to derive bounds on OPE coefficients and scaling dimensions from the constraints of crossing symmetry and unitarity. We also derive analytic results for the large spin spectrum using the lightcone expansion of the crossing equation. Our principal result is strong evidence that the $A_1$ theory realizes the minimal allowed central charge $(c=25)$ for any interacting $(2,0)$ theory. This implies that the full stress tensor four-point function of the $A_1$ theory is the unique unitary solution to the crossing symmetry equation at $c=25$. For this theory, we estimate the scaling dimensions of the lightest unprotected operators appearing in the stress tensor operator product expansion. We also find rigorous upper bounds for dimensions and OPE coefficients for a general interacting $(2,0)$ theory of central charge $c$. For large $c$, our bounds appear to be saturated by the holographic predictions obtained from eleven-dimensional supergravity.Beem, ChristopherLemos, MadalenaRastelli, Leonardovan Rees, Balt CWed, 22 Jul 2015 06:19:52 GMT20 Jul 2015arXiv:1507.05637https://cds.cern.ch/record/2036531Fluid dynamic propagation of initial baryon number perturbations on a Bjorken flow background
https://cds.cern.ch/record/2036505
Baryon number density perturbations offer a possible route to experimentally measure baryon number susceptibilities and heat conductivity of the quark gluon plasma. We study the fluid dynamical evolution of local and event-by-event fluctuations of baryon number density, flow velocity and energy density on top of a (generalised) Bjorken expansion. To that end we use a background-fluctuation splitting and a Bessel-Fourier decomposition for the fluctuating part of the fluid dynamical fields with respect to the azimuthal angle, the radius in the transverse plane and rapidity. We examine how the time evolution of linear perturbations depends on the equation of state as well as on shear viscosity, bulk viscosity and heat conductivity for modes with different azimuthal, radial and rapidity wave numbers. Finally we discuss how this information is accessible to experiments in terms of the transverse and rapidity dependence of correlation functions for baryonic particles in high energy nuclear collisions.Floerchinger, StefanMartinez, MauricioWed, 22 Jul 2015 06:19:22 GMT20 Jul 2015arXiv:1507.05569https://cds.cern.ch/record/2036505Higgs mass predictions of public NMSSM spectrum generators
https://cds.cern.ch/record/2036469
The publicly available spectrum generators for the NMSSM often lead to different predictions for the mass of the standard model-like Higgs boson even if using the same renormalization scheme and two-loop accuracy. Depending on the parameter point, the differences can exceed 5 GeV, and even reach 8 GeV for moderate superparticle masses of up to 2 TeV. It is shown here that these differences can be traced back to the calculation of the running standard model parameters entering all calculations, to the approximations used in the two-loop corrections included in the different codes, and to different choices for the renormalization conditions and scales. In particular, the importance of the calculation of the top Yukawa coupling is pointed out.Staub, FlorianAthron, PeterEllwanger, UlrichGrober, RamonaMuhlleitner, MargareteSlavich, PietroVoigt, AlexanderWed, 22 Jul 2015 06:16:30 GMT17 Jul 2015arXiv:1507.05093https://cds.cern.ch/record/2036469HELAC-Onia 2.0: an upgraded matrix-element and event generator for heavy quarkonium physics
https://cds.cern.ch/record/2033889
We present an upgraded version (denoted as version 2.0) of the program HELAC-Onia for the automated computation of heavy-quarkonium helicity amplitudes within non-relativistic QCD framework. The new code has been designed to include many new and useful features for practical phenomenological simulations. It is designed for job submissions under cluster enviroment for parallel computations via Python scripts. We have interfaced HELAC-Onia to the parton shower Monte Carlo programs Pythia 8 and QEDPS to take into account the parton-shower effects. Moreover, the decay module guarantees that the program can perform the spin-entangled (cascade-)decay of heavy quarkonium after its generation. We have also implemented a reweighting method to automatically estimate the uncertainties from renormalization and/or factorization scales as well as parton-distribution functions to weighted or unweighted events. A futher update is the possiblity to generate one-dimensional or two-dimensional plots encoded in the analysis files on the fly. Some dedicated examples are given at the end of the writeup.Shao, Hua-ShengTue, 14 Jul 2015 06:36:39 GMT13 Jul 2015arXiv:1507.03435https://cds.cern.ch/record/2033889The refractive index of relic gravitons
https://cds.cern.ch/record/2033850
The dynamical evolution of the refractive index of the tensor modes of the geometry produces a specific class of power spectra characterized by a blue (i.e. slightly increasing) slope which is directly determined by the competition of the slow-roll parameter and of the rate of variation of the refractive index. Throughout the conventional stages of the inflationary and post-inflationary evolution, the microwave background anisotropies measurements, the pulsar timing limits and the big-bang nucleosythesis constraints set stringent bounds on the refractive index and on its rate of variation. Within the physically allowed region of the parameter space the cosmic background of relic gravitons leads to a potentially large signal for the ground based detectors (in their advanced version) and for the proposed space-borne interferometers. Conversely, the lack of direct detection of the signal will set a qualitatively new bound on the dynamical variation of the refractive index.Giovannini, MassimoTue, 14 Jul 2015 06:35:11 GMT13 Jul 2015arXiv:1507.03456https://cds.cern.ch/record/2033850Probing the Charm Yukawa Coupling in Higgs + Charm Production
https://cds.cern.ch/record/2033432
We propose a new method to determine the coupling of the Higgs boson to charm quarks, via Higgs production in association with a charm-tagged jet: $pp\to hc$. As a first estimate, we find that at the LHC with 3000 fb$^{-1}$ it should be possible to derive a constraint of order one, relative to the SM value of the charm Yukawa coupling. As a byproduct of this analysis, we present an estimate of the exclusive $pp \to hD^{(*)}$ electroweak cross section. Within the SM, the latter turns out to be not accessible at the LHC even in the high-luminosity phase.Brivio, IlariaGoertz, FlorianIsidori, GinoMon, 13 Jul 2015 05:29:59 GMT10 Jul 2015arXiv:1507.02916https://cds.cern.ch/record/2033432No-Scale Inflation
https://cds.cern.ch/record/2032906
Supersymmetry is the most natural framework for physics above the TeV scale, and the corresponding framework for early-Universe cosmology, including inflation, is supergravity. No-scale supergravity emerges from generic string compactifications and yields a non-negative potential, and is therefore a plausible framework for constructing models of inflation. No-scale inflation yields naturally predictions similar to those of the Starobinsky model based on $R + R^2$ gravity, with a tilted spectrum of scalar perturbations: $n_s \sim 0.96$, and small values of the tensor-to-scalar perturbation ratio $r < 0.1$, as favoured by Planck and other data on the cosmic microwave background (CMB). Detailed measurements of the CMB may provide insights into the embedding of inflation within string theory as well as its links to collider physics.Ellis, JohnGarcia, Marcos A GNanopoulos, Dimitri VOlive, Keith AFri, 10 Jul 2015 06:05:04 GMT08 Jul 2015arXiv:1507.02308https://cds.cern.ch/record/2032906N=4 Supersymmetric AdS5 Vacua and their Moduli Spaces
https://cds.cern.ch/record/2032655
We classify the N=4 supersymmetric AdS5 backgrounds that arise as solutions of five-dimensional N=4 gauged supergravity. We express our results in terms of the allowed embedding tensor components and identify the structure of the associated gauge groups. We show that the moduli space of these AdS vacua is of the form SU(1,m)/(U(1)x SU(m)) and discuss our results regarding holographically dual N=2 SCFTs and their conformal manifolds.Louis, JanTriendl, HagenZagermann, MarcoThu, 09 Jul 2015 06:14:09 GMT06 Jul 2015arXiv:1507.01623https://cds.cern.ch/record/2032655Diboson resonant production in non-custodial composite Higgs models
https://cds.cern.ch/record/2032603
We show that the recently reported excess in resonant diboson production can be explained in the context of non-custodial composite Higgs models. Dibosons are generated via the s-channel exchange of massive vector bosons present in these models. We discuss the compatibility of the signal excess with other diboson experimental searches. We also discuss the tension between diboson production and other experimental tests of the model that include electroweak precision data, dilepton, dijet and top pair production and show that there is a region of parameter space in which they are all compatible with the excess.Carmona, AdrianDelgado, AntonioQuiros, MarianoSantiago, JoseThu, 09 Jul 2015 06:11:56 GMT07 Jul 2015arXiv:1507.01914https://cds.cern.ch/record/2032603Dark matter scenarios in a UV-complete model with Dirac gauginos
https://cds.cern.ch/record/2031552
We perform the first analysis of Dark Matter scenarios in a UV-complete model with Dirac Gauginos. The model under investigation is the Constrained Minimal Dirac Gaugino Supersymmetric Standard model (CMDGSSM) where the Majorana mass terms of gauginos vanish. However, $R$-symmetry is broken in the Higgs sector by an explicit and/or effective $B_\mu$-term. This causes a mass splitting between Dirac states in the fermion sector and the neutralinos, which provide the dark matter candidate, become pseudo-Dirac states. We discuss two scenarios: the universal case with all scalar masses unified at the GUT scale, and the case with non-universal Higgs soft-terms. We identify different regions in the parameter space which fullfil all constraints from the dark matter abundance, the limits from SUSY and direct dark matter searches and the Higgs mass. Most of these points can be tested with the next generation of direct dark matter detection experiments.Goodsell, Mark DKrauss, Manuel EMÃ¼ller, TobiasPorod, WernerStaub, FlorianTue, 07 Jul 2015 05:55:55 GMT03 Jul 2015arXiv:1507.01010https://cds.cern.ch/record/2031552Charged-Lepton Mixing and Lepton Flavor Violation
https://cds.cern.ch/record/2031545
We present a model for calculating charged-lepton mixing matrices. These matrices are an essential ingredient for predicting lepton flavor-violating rates in the lepton number nonuniversal models recently proposed to explain anomalies in B-meson decays. The model is based on work on "constrained flavor breaking" by Appelquist, Bai and Piai relating the charged-lepton mass matrix, M_l, to those for the up and down-type quarks, M_{u,d}. We use our recent model of lepton nonuniversality to illustrate the magnitudes of flavor-violating B-decay rates that might be expected. Decays with mu tau final states generally have the highest rates by far.Guadagnoli, DiegoLane, KennethTue, 07 Jul 2015 05:55:28 GMT06 Jul 2015arXiv:1507.01412https://cds.cern.ch/record/2031545Parton distributions with threshold resummation
https://cds.cern.ch/record/2031540
We construct a set of parton distribution functions (PDFs) in which fixed-order NLO and NNLO calculations are supplemented with soft-gluon (threshold) resummation up to NLL and NNLL accuracy respectively, suitable for use in conjunction with any QCD calculation in which threshold resummation is included at the level of partonic cross sections. These resummed PDF sets, based on the NNPDF3.0 analysis, are extracted from deep-inelastic scattering, Drell-Yan, and top quark pair production data, for which resummed calculations can be consistently used. We find that, close to threshold, the inclusion of resummed PDFs can partially compensate the enhancement in resummed matrix elements, leading to resummed hadronic cross-sections closer to the fixed-order calculation. On the other hand, far from threshold, resummed PDFs reduce to their fixed-order counterparts. Our results demonstrate the need for a consistent use of resummed PDFs in resummed calculations.Bonvini, MarcoMarzani, SimoneRojo, JuanRottoli, LucaUbiali, MariaBall, Richard DBertone, ValerioCarrazza, StefanoHartland, Nathan PTue, 07 Jul 2015 05:55:23 GMT03 Jul 2015arXiv:1507.01006https://cds.cern.ch/record/2031540Low Q^2 Weak Mixing Angle Measurements and Rare Higgs Decays
https://cds.cern.ch/record/2030725
A weighted average weak mixing angle theta_W derived from relatively low Q^2 experiments is compared with the Standard Model prediction obtained from precision measurements. The approximate 1.8 sigma discrepancy is fit with an intermediate mass (~ 10-35 GeV) "dark" Z boson Z_d, corresponding to a U(1)_d gauge symmetry of hidden dark matter, which couples to our world via kinetic and Z-Z_d mass mixing. Constraints on such a scenario are obtained from precision electroweak bounds and searches for the rare Higgs decays H -> Z Z_d -> 4 charged leptons at the LHC. The sensitivity of future anticipated low Q^2 measurements of sin^2 theta_W(Q^2) to intermediate mass Z_d is also illustrated. This dark Z scenario can provide interesting concomitant signals in low energy parity violating measurements and rare Higgs decays at the LHC, over the next few years.Davoudiasl, HoomanLee, Hye-SungMarciano, William JFri, 03 Jul 2015 05:52:45 GMT01 Jul 2015arXiv:1507.00352https://cds.cern.ch/record/2030725The PDF4LHC report on PDFs and LHC data: Results from Run I and preparation for Run II
https://cds.cern.ch/record/2030721
The accurate determination of the Parton Distribution Functions (PDFs) of the proton is an essential ingredient of the Large Hadron Collider (LHC) program. PDF uncertainties impact a wide range of processes, from Higgs boson characterisation and precision Standard Model measurements to New Physics searches. A major recent development in modern PDF analyses has been to exploit the wealth of new information contained in precision measurements from the LHC Run I, as well as progress in tools and methods to include these data in PDF fits. In this report we summarise the information that PDF-sensitive measurements at the LHC have provided so far, and review the prospects for further constraining PDFs with data from the recently started Run II. This document aims to provide useful input to the LHC collaborations to prioritise their PDF-sensitive measurements at Run II, as well as a comprehensive reference for the PDF-fitting collaborations.Rojo, JuanAccardi, AlbertoBall, Richard DCooper-Sarkar, Amandade Roeck, AlbertFarry, StephenFerrando, JamesForte, StefanoGao, JunHarland-Lang, LucianHuston, JoeyGlazov, AlexanderGouzevitch, MaximeGwenlan, ClaireLipka, KaterinaLisovyi, MykhailoMangano, MichelangeloNadolsky, PavelPerrozzi, LucaPlacakyte, RingaileRadescu, VoicaSalam, Gavin PThorne, RobertFri, 03 Jul 2015 05:51:08 GMT02 Jul 2015arXiv:1507.00556https://cds.cern.ch/record/2030721Color-Kinematics Duality for QCD Amplitudes
https://cds.cern.ch/record/2030454
We show that color-kinematics duality is present in tree-level amplitudes of quantum chromodynamics with massive flavored quarks. Starting with the color structure of QCD, we work out a new color decomposition for n-point tree amplitudes in a reduced basis of primitive amplitudes. These primitives, with k quark-antiquark pairs and (n-2k) gluons, are taken in the (n-2)!/k! Melia basis, and are independent under the color-algebra Kleiss-Kuijf relations. This generalizes the color decomposition of Del Duca, Dixon, and Maltoni to an arbitrary number of quarks. The color coefficients in the new decomposition are given by compact expressions valid for arbitrary gauge group and representation. Considering the kinematic structure, we show through explicit calculations that color-kinematics duality holds for amplitudes with general configurations of gluons and massive quarks. The new (massive) amplitude relations that follow from the duality can be mapped to a well-defined subset of the familiar BCJ relations for gluons. They restrict the amplitude basis further down to (n-3)!(2k-2)/k! primitives, for two or more quark lines. We give a decomposition of the full amplitude in that basis. The presented results provide strong evidence that QCD obeys the color-kinematics duality, at least at tree level. The results are also applicable to supersymmetric and D-dimensional extensions of QCD.Johansson, HenrikOchirov, AlexanderThu, 02 Jul 2015 06:13:17 GMT01 Jul 2015arXiv:1507.00332https://cds.cern.ch/record/2030454