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Ring Relations and Mirror Map from Branes
https://cds.cern.ch/record/2244365
We study the space of vacua of three-dimensional $\mathcal{N}=4$ theories from a novel approach building on the type IIB brane realization of the theory and in which the insertion of local chiral operators in the path integral is obtained from integrating out light modes in appropriate brane setups. Most of our analysis focuses on abelian quiver theories which can be realized as the low-energy theory of D3-D5-NS5 brane arrays. Their space of vacua contains a Higgs branch, parametrized by the vevs of half-BPS meson operators, and a Coulomb branch, parametrized by the vevs of half-BPS monopole operators. We show that the Higgs operators are inserted by adding F1 strings and D3 branes, while the Coulomb operators are inserted by adding D1 strings and D3 branes, with specific orientations, to the initial brane setup of the theory. This approach has two main advantages. First the ring relations describing the Higgs and Coulomb branches can be derived by looking at specific brane setups with multiple interpretations in terms of operator insertions. This provides a new derivation of the Coulomb branch quantum relations. Secondly the map between the Higgs and Coulomb operators of mirror dual theories is obtained in a trivial way from IIB S-duality.Assel, BenjaminSat, 04 Feb 2017 06:25:20 GMT2017-01-30CERN-TH-2017-018https://cds.cern.ch/record/22443652017018Simplified dark matter models with two Higgs doublets: I. Pseudoscalar mediators
https://cds.cern.ch/record/2244364
We study a new class of renormalisable simplified models for dark matter searches at the LHC that are based on two Higgs doublet models with an additional pseudoscalar mediator. In contrast to the spin-0 simplified models employed in analyses of Run I data these models are self-consistent, unitary and bounds from Higgs physics typically pose no constraints. Predictions for various missing transverse energy ($E_{T, \rm miss}$) searches are discussed and the reach of the 13 TeV LHC is explored. It is found that the proposed models provide a rich spectrum of complementary observables that lead to non-trivial constraints. We emphasise in this context the sensitivity of the $t\bar t + E_{T, \rm miss}$, mono-$Z$ and mono-Higgs channels, which yield stronger limits than mono-jet searches in large parts of the parameter space. Constraints from spin-0 resonance searches, electroweak precision measurements and flavour observables are also derived and shown to provide further important handles to constraint and to test the considered dark matter models.Bauer, MartinHaisch, UlrichKahlhoefer, FelixSat, 04 Feb 2017 06:25:10 GMT2017-01-25CERN-TH-2017-011https://cds.cern.ch/record/22443642017011On exponential suppression of the cosmological constant in non-SUSY strings at two loops and beyond
https://cds.cern.ch/record/2244363
Two independent criteria are presented that together guarantee exponential suppression of the two-loop cosmological constant in non-supersymmetric heterotic strings. They are derived by performing calculations in both the full string theory and in its underlying effective field theory, and come respectively from contributions that involve only physical untwisted states, and contributions that include orbifold twisted states. The criteria depend purely on the spectrum and charges, so a model that satisfies them will do so with no fine-tuning. An additional consistency condition (emerging from the so-called separating degeneration limit of the two-loop diagram) is that the one-loop cosmological constant must also be suppressed, by Bose-Fermi degeneracy in the massless spectrum. We remark that theories of this kind, that have continued exponential suppression to higher orders, can form the basis for a string implementation of the "naturalness without supersymmetry" idea.Abel, StevenStewart, Richard J.Sat, 04 Feb 2017 06:25:08 GMT2017-01-23IPPP-17-6https://cds.cern.ch/record/2244363176A model for pion-pion scattering in large-N QCD
https://cds.cern.ch/record/2243469
Following up on recent work by Caron-Huot et al. we consider a generalization of the old Lovelace-Shapiro model as a toy model for Pi-Pi scattering satisfying (most of) the properties expected to hold in ('t Hooft's) large-N limit of massless QCD. In particular, the model has asymptotically linear and parallel Regge trajectories at positive t, a positive leading Regge intercept $\alpha_0 < 1$, and an effective bending of the trajectories in the negative-t region producing a fixed branch point at J=0 for $t < t_0 < 0$. Fixed (physical) angle scattering can be tuned to match the power-like (including logarithmic corrections) behavior predicted by perturbative QCD: $A(s,t) ~ s^{-\beta} \log(s)^{-\gamma} F(\theta)$. Tree-level unitarity (i.e. positivity of residues for all values of s and J) imposes strong constraints on the allowed region in the alpha_0-beta-gamma parameter space, which nicely includes a physically interesting region around $\alpha_0 = 0.5$, $\beta = 2$ and $\gamma = 3$. The full consistency of the model would require an extension to multi-pion processes, a program we do not undertake in this paper.Veneziano, GabrieleYankielowicz, ShimonOnofri, EnricoTue, 31 Jan 2017 06:18:32 GMT2017-01-23CERN-TH-2017-002https://cds.cern.ch/record/22434692017002Rescattering effects in the hadronic-light-by-light contribution to the anomalous magnetic moment of the muon
https://cds.cern.ch/record/2243468
We present a first model-independent calculation of $\pi\pi$ intermediate states in the hadronic-light-by-light (HLbL) contribution to the anomalous magnetic moment of the muon $(g-2)_\mu$ that goes beyond the scalar QED pion loop. To this end we combine a recently developed dispersive description of the HLbL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, $a_\mu^{\pi\text{-box}}=-15.9(2)\times 10^{-11}$. We then construct suitable input for the $\gamma^*\gamma^*\to\pi\pi$ helicity partial waves based on a pion-pole left-hand cut and show that for the dominant charged-pion contribution this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the pion polarizability. This allows us to reliably estimate $S$-wave rescattering effects to the full pion box and leads to our final estimate for the sum of these two contributions: $a_\mu^{\pi\text{-box}} + a_{\mu,J=0}^{\pi\pi,\pi\text{-pole LHC}}=-24(1)\times 10^{-11}$.Colangelo, GilbertoHoferichter, MartinProcura, MassimilianoStoffer, PeterTue, 31 Jan 2017 06:18:31 GMT2017-01-23INT-PUB-17-005https://cds.cern.ch/record/224346817005A Simple Method to detect spontaneous CP Violation in multi-Higgs models
https://cds.cern.ch/record/2242544
For models with several Higgs doublets we present an alternative method to the one proposed by Branco, Gerard and Grimus, in 1984, to check whether or not CP is spontaneously violated in the Higgs potential. The previous method is powerful and rigorous. It requires the identification of a matrix $U$ corresponding to a symmetry of the Lagrangian and verifying a simple relation involving the vacuum expectation values. The nonexistence of such a matrix signals spontaneous CP violation. However, as the number of Higgs doublets increases, finding such a matrix $U$ may not be straightforward and it may turn out to be easier to analyse the potential by going to the so-called Higgs basis. The transformation to the Higgs basis is straightforward once the vacuum expectation values are known. The method proposed in this work is also powerful and rigorous and can be particularly useful to analyse models with more than two Higgs doublets and with continuous symmetries.Ogreid, O.M.Osland, P.Rebelo, M.N.Fri, 20 Jan 2017 06:23:00 GMT2017-01-17CERN-TH-2017-008https://cds.cern.ch/record/22425442017008Dimension-6 Operator Analysis of the CLIC Sensitivity to New Physics
https://cds.cern.ch/record/2242543
We estimate the possible accuracies of measurements at the proposed CLIC $e^+e^-$ collider of Higgs and $W^+W^-$ production at centre-of-mass energies up to 3TeV, incorporating also Higgsstrahlung projections at higher energies that had not been considered previously, and use them to explore the prospective CLIC sensitivities to decoupled new physics. We present the resulting constraints on the Wilson coefficients of dimension-6 operators in a model-independent approach based on the Standard Model effective field theory (SM EFT). The higher centre-of-mass energy of CLIC, compared to other projects such as the ILC and CEPC, gives it greater sensitivity to the coefficients of some of the operators we study. We find that CLIC Higgs measurements may be sensitive to new physics scales $\Lambda = \mathcal{O}(10)$TeV for individual operators, reduced to $\mathcal{O}(1)$ TeV sensitivity for a global fit marginalising over the coefficients of all contributing operators. We give some examples of the corresponding prospective constraints on specific scenarios for physics beyond the SM, including stop quarks and the dilaton/radion.Ellis, JohnRoloff, PhilippSanz, VeronicaYou, TevongFri, 20 Jan 2017 06:22:58 GMT2017-01-17KCL-PH-TH-2017-04https://cds.cern.ch/record/2242543201704Supergravity and its Legacy
https://cds.cern.ch/record/2242541
A personal recollection of events that preceded the construction of Supergravity and of some subsequent developments.Ferrara, S.Fri, 20 Jan 2017 06:22:54 GMT2017-01-12CERN-TH-2017-004https://cds.cern.ch/record/22425412017004Supersymmetric partition functions and the three-dimensional A-twist
https://cds.cern.ch/record/2242540
We study three-dimensional $\mathcal{N}=2$ supersymmetric gauge theories on $\mathcal{M}_{g,p}$, an oriented circle bundle of degree $p$ over a closed Riemann surface, $\Sigma_g$. We compute the $\mathcal{M}_{g,p}$ supersymmetric partition function and correlation functions of supersymmetric loop operators. This uncovers interesting relations between observables on manifolds of different topologies. In particular, the familiar supersymmetric partition function on the round $S^3$ can be understood as the expectation value of a so-called "fibering operator" on $S^2 \times S^1$ with a topological twist. More generally, we show that the 3d $\mathcal{N}=2$ supersymmetric partition functions (and supersymmetric Wilson loop correlation functions) on $\mathcal{M}_{g,p}$ are fully determined by the two-dimensional A-twisted topological field theory obtained by compactifying the 3d theory on a circle. We give two complementary derivations of the result. We also discuss applications to F-maximization and to three-dimensional supersymmetric dualities.Closset, CyrilKim, HeeyeonWillett, BrianFri, 20 Jan 2017 06:22:50 GMT2017-01-11CERN-TH-2017-006https://cds.cern.ch/record/22425402017006The $\Lambda$-parameter in 3-flavour QCD and $\alpha_s(m_Z)$ by the ALPHA collaboration
https://cds.cern.ch/record/2242539
We present results by the ALPHA collaboration for the $\Lambda$-parameter in 3-flavour QCD and the strong coupling constant at the electroweak scale, $\alpha_s(m_Z)$, in terms of hadronic quantities computed on the CLS gauge configurations. The first part of this proceedings contribution contains a review of published material \cite{Brida:2016flw,DallaBrida:2016kgh} and yields the $\Lambda$-parameter in units of a low energy scale, $1/L_{\rm had}$. We then discuss how to determine this scale in physical units from experimental data for the pion and kaon decay constants. We obtain $\Lambda_{\overline{\rm MS}}^{(3)} = 332(14)$ MeV which translates to $\alpha_s(M_Z)=0.1179(10)(2)$ using perturbation theory to match between 3-, 4- and 5-flavour QCD.Bruno, M.Dalla Brida, M.Fritzsch, P.Korzec, T.Ramos, A.Schaefer, S.Simma, H.Sint, S.Sommer, R.Fri, 20 Jan 2017 06:22:48 GMT2017-01-11CERN-TH-2016-262https://cds.cern.ch/record/22425392016262FRB 121102 Casts New Light on the Photon Mass
https://cds.cern.ch/record/2242538
The photon mass, $m_\gamma$, can in principle be constrained using measurements of the dispersion measures (DMs) of fast radio bursts (FRBs), once the FRB redshifts are known. The DM of the repeating FRB 121102 is known to $< 1$\%, a host galaxy has now been identified with high confidence,and its redshift, $z$, has now been determined with high accuracy: $z = 0.19273(8)$. Taking into account the plasma contributions to the DM from the Intergalactic medium (IGM) and the Milky Way, we use the data on FRB 121102 to derive the constraint $m_\gamma \lesssim 2.2 \times 10^{-14}$ eV c$^{-2}$ ($3.9 \times 10^{-50}$ kg). Since the plasma and photon mass contributions to DMs have different redshift dependences, they could in principle be distinguished by measurements of more FRB redshifts, enabling the sensitivity to $m_\gamma$ to be improved.Bonetti, LucaEllis, JohnMavromatos, Nikolaos E.Sakharov, Alexander S.Sarkisyan-Grinbaum, Edward K.Spallicci, Alessandro D. A. M.Fri, 20 Jan 2017 06:22:47 GMT2017-01-11KCL-PH-TH-2017-01https://cds.cern.ch/record/2242538201701Circular polarisation: a new probe of dark matter and neutrinos in the sky
https://cds.cern.ch/record/2242537
The study of anomalous electromagnetic emission in the sky is the basis of indirect searches for dark matter. It is also a powerful tool to constrain the radiative decay of active neutrinos. Until now, quantitative analyses have focused on the flux and energy spectrum of such an emission; polarisation has never been considered. Here we show that we could be missing out on an essential piece of information. The radiative decay of neutrinos, as well as the interactions of dark matter and neutrinos with Standard Model particles can generate a circular polarisation signal in X-rays or \gamma-rays. If observed, this could reveal important information about their spatial distribution and particle-antiparticle ratio, and could even reveal the nature of the high-energy particle physics processes taking place in astrophysical sites. The question of the observability of these polarised signatures and their separation from background astrophysical sources is left for future work.Bœhm, CélineDegrande, CélineMattelaer, OlivierVincent, Aaron C.Fri, 20 Jan 2017 06:22:45 GMT2017-01-10CERN-TH-2017-003https://cds.cern.ch/record/22425372017003Standard Model with spontaneously broken quantum scale invariance
https://cds.cern.ch/record/2242536
We explore the possibility that scale symmetry is a quantum symmetry broken only spontaneously and apply this idea to the Standard Model (SM) potential. We analyze the quantum corrections to the potential of the higgs field ($\phi$) in the classically scale invariant version of the SM ($m_\phi=0$ at tree level) extended by the dilaton ($\sigma$). The one-loop scalar potential is scale invariant, since the loop calculations preserve the scale symmetry, with the subtraction scale generated spontaneously by the dilaton vev, $\langle\sigma\rangle$. The potential contains new, non-polynomial (scale-invariant) operators of quantum origin, beyond the usual Coleman-Weinberg term (itself made scale-invariant). The Callan-Symanzik equation of the potential is verified in the presence of the gauge, Yukawa and the non-polynomial operators whose coefficients have non-zero beta functions. At the quantum level the higgs mass is protected although the theory is non-renormalizable, while the vacuum energy vanishes, following quantum scale invariance of the potential. We compare the scale-invariant one-loop potential to its counterpart computed in the "usual" regularization that breaks scale symmetry explicitly, in the presence at the tree level of non-polynomial operators.Ghilencea, D.M.Lalak, Z.Olszewski, P.Fri, 20 Jan 2017 06:22:45 GMT2016-12-29CERN-TH-2016-242https://cds.cern.ch/record/22425362016242Dark Matter's secret liaisons: phenomenology of a dark $U(1)$ sector with bound states
https://cds.cern.ch/record/2242534
Dark matter (DM) charged under a dark U(1) force appears in many extensions of the Standard Model, and has been invoked to explain anomalies in cosmic-ray data, as well as a self-interacting DM candidate. In this paper, we perform a comprehensive phenomenological analysis of such a model, assuming that the DM abundance arises from the thermal freeze-out of the dark interactions. We include, for the first time, bound-state effects both in the DM production and in the indirect detection signals, and quantify their importance for Fermi, AMS, and CMB experiments. We find that DM in the mass range 1 GeV to 100 TeV, annihilating into dark photons of MeV to GeV mass, is in conflict with observations. Instead, DM annihilation into heavier dark photons is viable. We point out that the late decays of multi-GeV dark photons can produce significant entropy and thus dilute the DM density. This can lower considerably the dark coupling needed to obtain the DM abundance, and in turn relax the existing constraints.Cirelli, MarcoPanci, PaoloPetraki, KalliopiSala, FilippoTaoso, MarcoFri, 20 Jan 2017 06:22:34 GMT2016-12-21CERN-TH-2016-255https://cds.cern.ch/record/22425342016255Dark Matter "Collider" from Inelastic Boosted Dark Matter
https://cds.cern.ch/record/2242533
We propose a novel dark matter (DM) detection strategy for the models with non-minimal dark sector. The main ingredients in the underlying DM scenario are a boosted DM particle and a heavier dark sector state. The relativistic DM impinged on target material scatters off inelastically to the heavier state which subsequently decays into DM along with lighter states including visible (Standard Model) particles. The expected signal event, therefore, accompanies a visible signature by the secondary cascade process associated with a recoiling of the target particle, differing from the typical neutrino signal not involving the secondary signature. We then discuss various kinematic features followed by DM detection prospects at large volume neutrino detectors with a model framework where a dark gauge boson is the mediator between the Standard Model particles and DM.Kim, DoojinPark, Jong-ChulShin, SeodongFri, 20 Jan 2017 06:22:30 GMT2016-12-20CERN-TH-2016-258https://cds.cern.ch/record/22425332016258The complete NLO corrections to dijet hadroproduction
https://cds.cern.ch/record/2242532
We study the production of jets in hadronic collisions, by computing all contributions proportional to $\alpha_S^n\alpha^m$, with $n+m=2$ and $n+m=3$. These correspond to leading and next-to-leading order results, respectively, for single-inclusive and dijet observables in a perturbative expansion that includes both QCD and electroweak effects. We discuss issues relevant to the definition of hadronic jets in the context of electroweak corrections, and present sample phenomenological predictions for the 13-TeV LHC. We find that both the leading and next-to-leading order contributions largely respect the relative hierarchy established by the respective coupling-constant combinations.Frederix, RikkertFrixione, StefanoHirschi, ValentinPagani, DavideShao, Hua-ShengZaro, MarcoFri, 20 Jan 2017 06:22:25 GMT2016-12-20CERN-TH-2016-250https://cds.cern.ch/record/22425322016250Ultra-Light Dark Matter Resonates with Binary Pulsars
https://cds.cern.ch/record/2242531
We consider the scenario where dark matter (DM) is represented by an ultra-light classical scalar field performing coherent periodic oscillations. We point out that such DM perturbs the dynamics of binary systems either through its gravitational field or via direct coupling to ordinary matter. This perturbation gets resonantly amplified if the frequency of DM oscillations is close to a (half-)integer multiple of the orbital frequency of the system and leads to a secular variation of the orbital period. We suggest to use binary pulsars as probes of this scenario and estimate their sensitivity. While the current accuracy of observations is not yet sufficient to probe the purely gravitational effect of DM, it already yields constraints on direct coupling that are competitive with other bounds. The sensitivity will increase with the upcoming radio observatories such as Square Kilometer Array.Blas, DiegoNacir, Diana LopezSibiryakov, SergeyFri, 20 Jan 2017 06:22:24 GMT2016-12-20CERN-TH-2016-257https://cds.cern.ch/record/22425312016257Non-gaussianity of the critical 3d Ising model
https://cds.cern.ch/record/2242530
We discuss the 4pt function of the critical 3d Ising model, extracted from recent conformal bootstrap results. We focus on the non-gaussianity Q - the ratio of the 4pt function to its gaussian part given by three Wick contractions. This ratio reveals significant non-gaussianity of the critical fluctuations. The bootstrap results are consistent with a rigorous inequality due to Lebowitz and Aizenman, which limits Q to lie between 1/3 and 1.Rychkov, SlavaSimmons-Duffin, DavidZan, BernardoFri, 20 Jan 2017 06:22:22 GMT2016-12-07CERN-TH-2016-249https://cds.cern.ch/record/22425302016249Exploring the squark flavour structure of the MSSM
https://cds.cern.ch/record/2241221
We present an extensive study of the MSSM parameter space allowing for general generation mixing in the squark sector. Employing an MCMC algorithm, we establish the parameter ranges which are allowed with respect to various experimental and theoretical constraints. Based on this analysis, we propose benchmark scenarios for future studies. Moreover, we discuss aspects of signatures at the LHC.De Causmaecker, KarenFuks, BenjaminHerrmann, BjörnMahmoudi, FarvahO'Leary, BenPorod, WernerSekmen, SezenStrobbe, NadjaWed, 11 Jan 2017 06:31:05 GMT2017-01-06LAPTH-CONF-065-16https://cds.cern.ch/record/224122106516Naturalness of asymptotically safe Higgs
https://cds.cern.ch/record/2241220
We introduce a model that contains a Higgs-like scalar with gauge, Yukawa and quartic interactions that enter a perturbative asymptotically safe regime at energies above a scale $\Lambda$. The model serves as a concrete example to test whether scalars masses unavoidably receive quantum correction of order $\Lambda$. The answer is that scalars can be naturally lighter. Although we do not have an answer to whether the Standard Model hypercharge coupling growth towards a Landau pole around $\Lambda \sim 10^{40}$ GeV can be tamed by non-perturbative asymptotic safety, our toy-SM shows that such a possibility is worth exploring. In fact, if successful, it might also offer an explanation for the unbearable lightness of the Higgs.Pelaggi, Giulio MariaSannino, FrancescoStrumia, AlessandroVigiani, ElenaWed, 11 Jan 2017 06:31:05 GMT2017-01-05CERN-TH-2017-001https://cds.cern.ch/record/22412202017001SUSY Meets Her Twin
https://cds.cern.ch/record/2236791
We investigate the general structure of mirror symmetry breaking in the Twin Higgs scenario. We show, using the IR effective theory, that a significant gain in fine tuning can be achieved if the symmetry is broken hardly. We emphasize that weakly coupled UV completions can naturally accommodate this scenario. We analyze SUSY UV completions and present a simple Twin SUSY model with a tuning of around 10% and colored superpartners as heavy as 2 TeV. The collider signatures of general Twin SUSY models are discussed with a focus on the extended Higgs sectors.Katz, AndreyMariotti, AlbertoPokorski, StefanRedigolo, DiegoZiegler, RobertFri, 02 Dec 2016 11:49:30 GMT25 Nov 2016arXiv:1611.08615https://cds.cern.ch/record/2236791['arXiv:1611.08615']arXiv:1611.08615LHC Signals from Cascade Decays of Warped Vector Resonances
https://cds.cern.ch/record/2236694
Recently (arXiv:1608.00526), a new framework for warped higher-dimensional compactifications with "bulk" standard model (SM) was proposed: in addition to the UV (Planck scale) and IR (a couple of TeV) branes, there is an intermediate brane, taken to be around 10 TeV. The SM matter and Higgs fields propagate from the UV brane down to this intermediate brane only, while gauge and gravity fields propagate in the entire bulk. Such a configuration renders the lightest gauge Kaluza-Klein (KK) states within LHC reach, simultaneously satisfying flavor and CP constraints. In addition, the usual leading decay modes of the lightest KK gauge bosons into top and Higgs bosons are suppressed. This effect permits erstwhile subdominant channels to become significant. These include flavor-universal decays to SM fermions and Higgs bosons, and a novel channel - decay to a radion and a SM gauge boson, followed by radion decay to a pair of SM gauge bosons. In this work, we first delineate the parameter space where the above mentioned cascade decay of gauge KK particles dominates, and thereby can be the discovery mode at the LHC. We then perform a detailed analysis of the LHC signals from this model, finding that 300/fb suffices for evidence of KK-gluon in tri-jet, jet + di-photon and jet + di-boson channels. However, KK photon in photon + di-jet, and KK-W in leptonic W + di-jet require 3000/fb. The crucial feature of this decay chain is a "double" resonance, i.e. 3-particle and 2-particle invariant mass peaks, corresponding to the KK gauge boson and the radion respectively.Agashe, Kaustubh S.Collins, JackDu, PeizhiHong, SungwooKim, DoojinMishra, Rashmish K.Fri, 02 Dec 2016 11:44:28 GMT30 Nov 2016arXiv:1612.00047https://cds.cern.ch/record/2236694['arXiv:1612.00047']arXiv:1612.00047Determining the CP nature of spin-0 mediators in associated production of dark matter and $t \bar t$ pairs
https://cds.cern.ch/record/2236681
In the framework of spin-0 $s$-channel simplified models, we explore the possibility of assessing the structure of dark matter interactions through the associate production of dark matter and $t\bar{t}$ pairs. To this purpose, final states with two leptons are considered and the kinematic properties of the dilepton system is studied. We develop a realistic analysis strategy and provide a detailed evaluation of the achievable sensitivity for the dark matter signal assuming integrated luminosities of $300 \, {\rm fb}^{-1}$ and $3 \, {\rm ab}^{-1}$ at the 14 TeV LHC. Furthermore, upper limits on the mediator masses for which the two different CP hypotheses can be distinguished are derived. The obtained limits on the signal strengths are finally translated into constraints on the parameter space of two spin-0 simplified models including a scenario with an extended Higgs sector.Haisch, UlrichPani, PriscillaPolesello, GiacomoFri, 02 Dec 2016 11:44:23 GMT29 Nov 2016CERN-TH-2016-243https://cds.cern.ch/record/22366812016243Phenomenological analysis of associated production of $Z^0+b$ in the $b \rightarrow J/\psi X$ decay channel at the LHC
https://cds.cern.ch/record/2236670
The ATLAS collaboration recently reported on the first observation of associated-production of a $Z^0$ boson with a $J/\psi$. We recently claimed that the corresponding yield of the {\it prompt} $J/\psi$ was dominated by double parton scatterings in the ATLAS acceptance with a somewhat small value of $\sigma_{\rm eff}$. We also found out that single parton scatterings were only dominant at large transverse momenta. We present here the first phenomenological analysis of another part of the ATLAS data sample, namely of a $Z^0$ boson plus a {\it non-prompt} $J/\psi$. Our study is performed at next-to-leading order in $\alpha_s$ and includes parton-shower effects via the {\sc\small MadGraph5_aMC@NLO} framework. We find out that the data, unlike the case of prompt $J/\psi+Z^0$, do not hint at significant DPS contributions. Owing to the current experimental and theoretical uncertainties, there is still a room for these but with a lower limit of $\sigma_{\rm eff}$ close to 5 mb. We stress the importance of QCD corrections to account for the ATLAS data.Lansberg, Jean-PhilippeShao, Hua-ShengFri, 02 Dec 2016 11:44:21 GMT28 Nov 2016CERN-TH-2016-244https://cds.cern.ch/record/22366702016244Stringy bounces and gradient instabilities
https://cds.cern.ch/record/2236545
Bouncing solutions are obtained from a generally covariant action characterized by a potential which is a nonlocal functional of the dilaton field at two separated space-time points. Gradient instabilities are shown to arise in this context but they are argued to be nongeneric. After performing a gauge-invariant and frame-invariant derivation of the evolution equations of the fluctuations, a heuristic criterium for the avoidance of pathological instabilities is proposed and corroborated by a number of explicit examples that turn out to be compatible with a quasi-flat spectrum of curvature inhomogeneities for typical wavelengths larger than the Hubble radius.Giovannini, MassimoFri, 02 Dec 2016 11:42:16 GMT01 Dec 2016arXiv:1612.00346https://cds.cern.ch/record/2236545['arXiv:1612.00346']arXiv:1612.00346