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Scaling laws and sum rules for the B-mode polarization
https://cds.cern.ch/record/1646257
The formation of the microwave background polarization anisotropies is investigated when the stochastic Faraday rate is stationary, random and Markovian. The scaling properties of the polarization power spectra and of their nonlinear combinations are scrutinized as a function of the comoving frequency. It is argued that each frequency channel of a given experiment measuring simultaneously the E-mode and the B-mode spectra can be analyzed in this framework with the aim of testing the physical origin of the polarization in a model-independent perspective.Giovannini, MassimoTue, 04 Feb 2014 03:16:51 GMThttps://cds.cern.ch/record/1646257Higgs pair production at the LHC with NLO and parton-shower effects
https://cds.cern.ch/record/1645571
We present predictions for the SM-Higgs-pair production channels of relevance at the LHC: gluon-gluon fusion, VBF, and top-pair, W, Z and single-top associated production. All these results are at the NLO accuracy in QCD, and matched to parton showers by means of the MC@NLO method; hence, they are fully differential. With the exception of the gluon-gluon fusion process, for which a special treatment is needed in order to improve upon the infinite-top-mass limit, our predictions are obtained in a fully automatic way within the publicly available MadGraph5_aMC@NLO framework. We show that for all channels in general, and for gluon-gluon fusion and top-pair associated production in particular, NLO corrections reduce the theoretical uncertainties, and are needed in order to arrive at reliable predictions for total rates as well as for distributions.Frixione, SThu, 30 Jan 2014 07:28:03 GMThttps://cds.cern.ch/record/1645571Energy-energy correlations in N=4 Supersymmetric Yang-Mills Theory
https://cds.cern.ch/record/1644580
We present a new approach to computing energy-energy correlations in gauge theories that exploits their relation to correlation functions and bypasses the use of scattering amplitudes. We illustrate its power by calculating energy-energy correlations in the maximally supersymmetric Yang-Mills theory (N=4 SYM) in the next-to-leading order approximation.Hohenegger, SThu, 23 Jan 2014 09:52:20 GMThttps://cds.cern.ch/record/1644580No-hair conjectures, primordial shear and protoinflationary initial conditions
https://cds.cern.ch/record/1637584
Anisotropic inflationary background geometries are analyzed in the context of an extended gauge action where the electric and magnetic susceptibilities are not bound to coincide and depend on the inflaton field. After deriving various classes of solutions with electric and magnetic hairs, we discuss the problem of the initial boundary conditions of the shear parameter and consider a globally neutral plasma as a possible relic of a preinflationary stage of expansion. While electric hairs are washed out by the finite value of the protoinflationary conductivity, magnetic hairs can persist and introduce a tiny amount of shear causing a different inflationary rate of expansion along orthogonal spatial directions. The plasma interactions are a necessary criterion to discriminate between physical and unphysical initial conditions but they are not strictly sufficient to warrant the stability of a given magnetic solution.Giovannini, MassimoWed, 18 Dec 2013 03:25:30 GMThttps://cds.cern.ch/record/1637584Rescuing Quadratic Inflation
https://cds.cern.ch/record/1633901
Inflationary models based on a single scalar field $\phi$ with a quadratic potential $V = \frac{1}{2} m^2 \phi^2$ are disfavoured by the recent Planck constraints on the scalar index, $n_s$, and the tensor-to-scalar ratio for cosmological density perturbations, $r_T$. In this paper we study how such a quadratic inflationary model can be rescued by postulating additional fields with quadratic potentials, such as might occur in sneutrino models, which might serve as either curvatons or supplementary inflatons. Introducing a second scalar field reduces but does not remove the pressure on quadratic inflation, but we find a sample of three-field models that are highly compatible with the Planck data on $n_s$ and $r_T$. We exhibit a specific three-sneutrino example that is also compatible with the data on neutrino mass difference and mixing angles.Fairbairn, MalcolmFri, 06 Dec 2013 03:23:21 GMThttps://cds.cern.ch/record/1633901Dynamical sectors of a relativistic two particle model
https://cds.cern.ch/record/1633528
We reconsider a model of two relativistic particles interacting via a multiplicative potential, as an example of a simple dynamical system with sectors, or branches, with different dynamics and degrees of freedom.The presence or absence of sectors depends on the values of rest masses. Some aspects of the canonical quantization are described. The model could be interpreted as a bigravity model in one dimension.Gomis, JoaquimThu, 05 Dec 2013 03:17:32 GMThttps://cds.cern.ch/record/1633528Study of the 125 GeV Standard Model Higgs Boson Partial Widths and Branching Fractions
https://cds.cern.ch/record/1631498
The discovery of the Higgs boson, with mass known to better than the percent level, enables for the first time precision Higgs boson analyses. Toward this goal, we define an expansion formalism of the Higgs boson partial widths and branching fractions that facilitates such studies. This expansion yields the observables as a perturbative expansion around reference values of Standard Model input observables (quark masses, QCD coupling constant, etc.). We compute the coefficients of the expansion using state-of-the-art results. We also study the various sources of uncertainties in computing the partial widths and branching fractions more precisely. We discuss the impact of these results with efforts to discern new physics through precision Higgs boson studies.Lee, Seung JWed, 27 Nov 2013 03:22:50 GMThttps://cds.cern.ch/record/1631498Monotop phenomenology at the Large Hadron Collider
https://cds.cern.ch/record/1631460
We investigate new physics scenarios where systems comprised of a single top quark accompanied by missing transverse energy, dubbed monotops, can be produced at the LHC. Following a simplified model approach, we describe all possible monotop production modes via an effective theory and estimate the sensitivity of the LHC, assuming 20 fb$^{-1}$ of collisions at a center-of-mass energy of 8 TeV, to the observation of a monotop state. Considering both leptonic and hadronic top quark decays, we show that large fractions of the parameter space are reachable and that new physics particles with masses ranging up to 1.5 TeV can leave hints within the 2012 LHC dataset, assuming moderate new physics coupling strengths.Andrea, JeremyWed, 27 Nov 2013 03:19:46 GMThttps://cds.cern.ch/record/1631460JEWEL 2.0.0 - Directions for Use
https://cds.cern.ch/record/1623958
In this publication the first official release of the JEWEL 2.0.0 code is presented. JEWEL is a Monte Carlo event generator simulating QCD jet evolution in heavy-ion collisions. It treats the interplay of QCD radiation and re-scattering in a medium with fully microscopic dynamics in a consistent perturbative framework with minimal assumptions. After a qualitative introduction into the physics of JEWEL detailed information about the practical aspects of using the code is given.Zapp, Korinna CMon, 04 Nov 2013 10:11:20 GMThttps://cds.cern.ch/record/1623958Constraints on light mediators: confronting dark matter searches with B physics
https://cds.cern.ch/record/1620383
Light scalars appear in many well-motivated extensions of the Standard Model including supersymmetric models with additional gauge singlets. Such scalars could mediate the interactions between dark matter and nuclei, giving rise to the tentative signals observed by several dark matter direct detection experiments including CDMS-Si. In this letter, we derive strong new limits on light scalar mediators by using the LHCb, Belle and BaBar searches for rare $\Upsilon$ and B decays. These limits rule out significant parts of the parameter space favored by CDMS-Si. Nevertheless, as current searches are not optimized for investigating weakly coupled light scalars, a further increase in experimental sensitivity could be achieved by relaxing requirements in the event selection.Staub, FlorianMon, 28 Oct 2013 03:12:34 GMThttps://cds.cern.ch/record/1620383A No-Scale Framework for Sub-Planckian Physics
https://cds.cern.ch/record/1611246
We propose a minimal model framework for physics below the Planck scale with the following features: (i) it is based on no-scale supergravity, as favoured in many string compactifications, (ii) it incorporates Starobinsky-like inflation, and hence is compatible with constraints from the Planck satellite, (iii) the inflaton may be identified with a singlet field in a see-saw model for neutrino masses, providing an efficient scenario for reheating and leptogenesis, (iv) supersymmetry breaking occurs with an arbitrary scale and a cosmological constant that vanishes before radiative corrections, (v) regions of the model parameter space are compatible with all LHC, Higgs and dark matter constraints.Nanopoulos, Dimitri VFri, 18 Oct 2013 02:16:12 GMThttps://cds.cern.ch/record/1611246Holographic Lattices Give the Graviton a Mass
https://cds.cern.ch/record/1610732
We discuss the DC conductivity of holographic theories with translational invariance broken by a background lattice. We show that the presence of the lattice induces an effective mass for the graviton via a gravitational version of the Higgs mechanism. This allows us to obtain, at leading order in the lattice strength, an analytic expression for the DC conductivity in terms of the size of the lattice at the horizon. In locally critical theories this leads to a power law resistivity that is in agreement with an earlier field theory analysis of Hartnoll and Hofman.Tong, DavidWed, 16 Oct 2013 02:17:58 GMThttps://cds.cern.ch/record/1610732Revisiting slepton pair production at the Large Hadron Collider
https://cds.cern.ch/record/1609150
Motivated by the shift in experimental attention towards electroweak supersymmetric particle production at the CERN LHC, we update in this paper our precision predictions at next-to-leading order of perturbative QCD matched to resummation at the next-to-leading logarithmic accuracy for direct slepton pair production in proton-proton collisions. Simplified models, now commonly adopted by the experimental collaborations for selectrons and smuons as well as mixing staus, are used as benchmarks for total cross sections at achieved and future center-of-mass energies. They are presented together with the corresponding scale and parton density uncertainties in graphical and tabular form for future reference. Using modern Monte Carlo techniques, we also reanalyze recent ATLAS and CMS slepton searches in light of our precision cross sections and for various assumptions on the decomposition of the sleptons and their neutralino decay products.Klasen, MichaelFri, 11 Oct 2013 02:20:59 GMThttps://cds.cern.ch/record/1609150Flavor and Collider Signatures of Asymmetric Dark Matter
https://cds.cern.ch/record/1609136
We consider flavor constraints on, and collider signatures of, Asymmetric Dark Matter (ADM) via higher dimension operators. In the supersymmetric models we consider, R-parity violating (RPV) operators carrying B-L interact with n dark matter (DM) particles X through an interaction of the form W = X^n O_{B-L}, where O_{B-L} = q l d^c, u^c d^c d^c, l l e^c. This interaction ensures that the lightest ordinary supersymmetric particle (LOSP) is unstable to decay into the X sector, leading to a higher multiplicity of final state particles and reduced missing energy at a collider. Flavor-violating processes place constraints on the scale of the higher dimension operator, impacting whether the LOSP decays promptly. While the strongest limitations on RPV from n-\bar{n} oscillations and proton decay do not apply to ADM, we analyze the constraints from meson mixing, mu-e conversion, mu -> 3 e and b -> s l^+ l^-. We show that these flavor constraints, even in the absence of flavor symmetries, allow parameter space for prompt decay to the X sector, with additional jets and leptons in exotic flavor combinations. We study the constraints from existing 8 TeV LHC SUSY searches with (i) 2-6 jets plus missing energy, and (ii) 1-2 leptons, 3-6 jets plus missing energy, comparing the constraints on ADM-extended supersymmetry with the usual supersymmetric simplified models.Zurek, Kathryn MFri, 11 Oct 2013 02:19:21 GMThttps://cds.cern.ch/record/1609136Inflationary susceptibilities, duality and large-scale magnetic fields generation
https://cds.cern.ch/record/1606600
We investigate what can be said about the interaction of scalar fields with Abelian gauge fields during a quasi-de Sitter phase of expansion and under the assumption that the electric and the magnetic susceptibilities do not coincide. The duality symmetry, transforming the magnetic susceptibility into the inverse of the electric susceptibility, exchanges the magnetic and electric power spectra. The mismatch between the two susceptibilities determines an effective refractive index affecting the evolution of the canonical fields. The constraints imposed by the duration of the inflationary phase and by the magnetogenesis requirements pin down the rate of variation of the susceptibilities that is consistent with the observations of the magnetic field strength over astrophysical and cosmological scales but avoids back-reaction problems. The parameter space of this magnetogenesis scenario is wider than in the case when the susceptibilities are equal, as it happens when the inflaton or some other spectator field is solely coupled to the standard gauge kinetic term.Giovannini, MassimoTue, 08 Oct 2013 02:24:05 GMThttps://cds.cern.ch/record/1606600Polarized Parton Distributions at an Electron-Ion Collider
https://cds.cern.ch/record/1605357
We study the potential impact of inclusive deep-inelastic scattering data from a future electron-ion collider (EIC) on longitudinally polarized parton distribution (PDFs). We perform a PDF determination using the NNPDF methodology, based on sets of deep-inelastic EIC pseudodata, for different realistic choices of the electron and proton beam energies. We compare the results to our current polarized PDF set, NNPDFpol1.0, based on a fit to fixed-target inclusive DIS data. We show that the uncertainties on the first moments of the polarized quark singlet and gluon distributions are substantially reduced in comparison to NNPDFpol1.0, but also that more measurements may be needed to ultimately pin down the size of the gluon contribution to the nucleon spin.Forte, StefanoThu, 03 Oct 2013 02:19:09 GMThttps://cds.cern.ch/record/1605357Multilepton signals of gauge mediated supersymmetry breaking at the LHC
https://cds.cern.ch/record/1604961
We investigate multilepton LHC signals arising from electroweak processes involving sleptons. We consider the framework of general gauge mediated supersymmetry breaking, focusing on models where the low mass region of the superpartner spectrum consists of the three generations of charged sleptons and the nearly massless gravitino. We demonstrate how such models can provide an explanation for the anomalous four lepton events recently observed by the CMS collaboration, while satisfying other existing experimental constraints. The best fit to the CMS data is obtained for a selectron/smuon mass of around 145 GeV and a stau mass of around 90 GeV. These models also give rise to final states with more than four leptons, offering alternative channels in which they can be probed and we estimate the corresponding production rates at the LHC.De Causmaecker, KarenWed, 02 Oct 2013 02:22:04 GMThttps://cds.cern.ch/record/1604961Non-Perturbative Nekrasov Partition Function from String Theory
https://cds.cern.ch/record/1603599
We calculate gauge instanton corrections to a class of higher derivative string effective couplings introduced in [1]. We work in Type I string theory compactified on K3xT2 and realise gauge instantons in terms of D5-branes wrapping the internal space. In the field theory limit we reproduce the deformed ADHM action on a general {\Omega}-background from which one can compute the non-perturbative gauge theory partition function using localisation. This is a non-perturbative extension of [1] and provides further evidence for our proposal of a string theory realisation of the {\Omega}-background.Florakis, IoannisFri, 27 Sep 2013 02:52:00 GMThttps://cds.cern.ch/record/1603599Production processes at extremely high energies
https://cds.cern.ch/record/1602560
The production processes are identified that contribute to the rise of the total cross section in proton-proton scattering at extremely high energies, s->~. At such energies, the scattering can be described by a black disk (completely absorptive) with a radius expanding logarithmically with energy surrounded by a gray fringe (partially absorptive). For the leading term of (lns)^2 in the increasing total cross section, the gray fringe is neglected, and geometrical optics is generalized to production processes. It is known that half of the rise in the total cross section is due to elastic scattering. The other half is found to originate from the production of jets with relatively small momenta in the center-of-mass system.Wu, Sau LanMon, 23 Sep 2013 13:40:19 GMThttps://cds.cern.ch/record/1602560Naive Dimensional Analysis Counting of Gauge Theory Amplitudes and Anomalous Dimensions
https://cds.cern.ch/record/1597342
We show that naive dimensional analysis (NDA) is equivalent to the result that L-loop scattering amplitudes have perturbative order N=L+Delta, with a shift Delta that depends on the NDA-weight of operator insertions. The NDA weight of an operator is defined in this paper, and the general NDA formula for perturbative order N is derived. The formula is used to explain why the one-loop anomalous dimension matrix for dimension-six operators in the Standard Model effective field theory has entries with perturbative order ranging from 0 to 4. The results in this paper are valid for an arbitrary effective field theory, and they constrain the coupling constant dependence of anomalous dimensions and scattering amplitudes in a general effective field theory.Manohar, Aneesh VThu, 05 Sep 2013 02:16:27 GMThttps://cds.cern.ch/record/1597342Cosmological Parameter Estimation with Large Scale Structure Observations
https://cds.cern.ch/record/1595874
We estimate the sensitivity of future galaxy surveys to cosmological parameters, using the redshift dependent angular power spectra of galaxy number counts, $C_\ell(z_1,z_2)$, calculated with all relativistic corrections at first order in perturbation theory. We pay special attention to the redshift dependence of the non-linearity scale and present Fisher matrix forecasts for Euclid-like and DES-like galaxy surveys. We compare the standard $P(k)$ analysis with the new $C_\ell(z_1,z_2)$ method. We show that for surveys with photometric redshifts the new analysis performs significantly better than the $P(k)$ analysis. For spectroscopic redshifts, however, the large number of redshift bins which would be needed to fully profit from the redshift information, is severely limited by shot noise. We also identify surveys which can measure the lensing contribution and we study the monopole, $C_0(z_1,z_2)$.Montanari, FrancescoThu, 29 Aug 2013 04:19:20 GMThttps://cds.cern.ch/record/1595874Lepton Dipole Moments in Supersymmetric Low-Scale Seesaw Models
https://cds.cern.ch/record/1581640
We study the anomalous magnetic and electric dipole moments of charged leptons in supersymmetric low-scale seesaw models with right-handed neutrino superfields. We consider a minimally extended framework of minimal supergravity, by assuming that CP violation originates from complex soft SUSY-breaking bilinear and trilinear couplings associated with the right-handed sneutrino sector. We present numerical estimates of the muon anomalous magnetic moment and the electron electric dipole moment (EDM), as functions of key model parameters, such as the Majorana mass scale mN and tan(\beta). In particular, we find that the contributions of the singlet heavy neutrinos and sneutrinos to the electron EDM are naturally small in this model, of order 10^{-27} - 10^{-28} e cm, and can be probed in the present and future experiments.Pilaftsis, ApostolosMon, 19 Aug 2013 02:09:03 GMThttps://cds.cern.ch/record/1581640Colliding clusters and dark matter self-interactions
https://cds.cern.ch/record/1581350
When a dark matter halo moves through a background of dark matter particles, self-interactions can lead to both deceleration and evaporation of the halo and thus shift its centroid relative to the collisionless stars and galaxies. We study the magnitude and time evolution of this shift for two classes of dark matter self-interactions, viz. frequent self-interactions with small momentum transfer (e.g. due to long-range interactions) and rare self-interactions with large momentum transfer (e.g. contact interactions), and find important differences between the two cases. We find that neither effect can be strong enough to completely separate the dark matter halo from the galaxies, if we impose conservative bounds on the self-interaction cross-section. The majority of both populations remain bound to the same gravitational potential and the peaks of their distributions are therefore always coincident. Consequently any apparent separation is mainly due to particles which are leaving the gravitational potential, so will be largest shortly after the collision but not observable in evolved systems. Nevertheless the fraction of collisions with large momentum transfer is an important characteristic of self-interactions, which can potentially be extracted from observational data and provide an important clue as to the nature of dark matter.Schmidt-Hoberg, KaiFri, 16 Aug 2013 02:09:28 GMThttps://cds.cern.ch/record/1581350Invariant scalar product on extended Poincare algebra
https://cds.cern.ch/record/1574524
Two methods can be used to calculate explicitly the Killing form on the Lie algebras. The first one is a direct calculation of the traces of the generators in a matrix representation of the algebra, and the second one is the usage of the group invariance of the scalar product. We use both methods in our calculation of the scalar product on the extended Poincare algebra in order to have a cross check of our results. The algebra is infinite-dimensional and requires careful treatment of the infinities. The scalar product on the extended algebra found by both methods coincides and the important conclusion which follows is that Poincare generators are orthogonal to the gauge generators.Savvidy, GeorgeWed, 14 Aug 2013 02:19:14 GMThttps://cds.cern.ch/record/1574524On periodically driven AdS/CFT
https://cds.cern.ch/record/1571117
We use the AdS/CFT correspondence to study a thermally isolated conformal field theory in four dimensions which undergoes a repeated deformation by an external periodic time-dependent source coupled to an operator of dimension Delta. The initial state of the theory is taken to be at a finite temperature. We compute the energy dissipated in the system as a function of the frequency and of the dimension Delta of the perturbing operator. This is done in the linear response regime. In order to study the details of thermalization in the dual field theory, the leading-order backreaction on the AdS black brane metric is computed. The evolution of the event and the apparent horizons is monitored; the increase of area in each cycle coincides with the increase in the equilibrium entropy corresponding to the amount of energy dissipated. The time evolution of the entanglement entropy of a spherical region and that of the two-points function of a probe operator with a large dimension are also inspected; we find a delay in the thermalization of these quantities which is proportional to the size of the region which is being probed. Thus, the delay is more pronounced in the infrared. We comment on a possible transition in the time evolution of the energy fluctuations.Elitzur, ShmuelMon, 12 Aug 2013 02:13:14 GMThttps://cds.cern.ch/record/1571117