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Majorana Fermions, Supersymmetry Breaking, and Born-Infeld Theory
https://cds.cern.ch/record/2057959
This review is devoted to highlight some aspects of the relevance of Majorana fermions in rigid supersymmetry breaking in four spacetime dimensions. After introducing some basic facts on spinors, and on their symmetries and reality properties, we consider Goldstino actions describing partial breaking of rigid supersymmetry, then focussing on Born-Infeld non-linear theory, its duality symmetry, and its supersymmetric extensions, also including multi-field generalizations exhibiting doubly self-duality.Ferrara, SergioMarrani, AlessioYeranyan, ArmenThu, 08 Oct 2015 06:23:31 GMT06 Oct 2015arXiv:1510.01658https://cds.cern.ch/record/2057959The Supersoft and Super-Natural Supersymmetry
https://cds.cern.ch/record/2057924
The super-natural Supersymmetry (SUSY) provides an elegant solution to the SUSY electroweak fine-tuning (EWFT) problem, and the Supersymmetric Standard Models (SSMs) with Dirac gauginos have the appealing supersoft property that they only cause finite contributions to scalar masses. Because the EWFT issue in this kind of models has not been addressed so far, we analyse it in the minimal $R$-symmetric SSM. Considering gauge mediated SUSY breaking with conformal sequestering, we find that the naive EWFT measure is similar to the other SSMs, except the minor improvements due to supersoft property and extra loop contributions to the Higgs boson mass. We present an effective super-natural SUSY condition: all dimensionful parameters, which give large EWFT measures, are correlated. With such a condition, we show explicitly a precise cancellation between the dominant terms that contribute to the EWFT. The resulting EWFT measure can be of unit order even for supersymmetric particle masses and $\mu$-terms in the TeV range.Ding, RanLi, TianjunStaub, FlorianZhu, BinThu, 08 Oct 2015 06:22:51 GMT05 Oct 2015arXiv:1510.01328https://cds.cern.ch/record/2057924An MCMC study of general squark flavour mixing in the MSSM
https://cds.cern.ch/record/2057379
We present an extensive study of non-minimally flavour violating (NMFV) terms in the Lagrangian of the Minimal Supersymmetric Standard Model (MSSM). We impose a variety of theoretical and experimental constraints and perform a detailed scan of the parameter space by means of a Markov Chain Monte-Carlo (MCMC) setup. This represents the first study of several non-zero flavour-violating elements within the MSSM. We present the results of the MCMC scan with a special focus on the flavour-violating parameters. Based on these results, we define benchmark scenarios for future studies of NMFV effects at the LHC.Herrmann, BjörnDe Causmaecker, KarenFuks, BenjaminMahmoudi, FarvahO'Leary, BenPorod, WernerSekmen, SezenStrobbe, NadjaTue, 06 Oct 2015 05:47:32 GMT05 Oct 2015arXiv:1510.01159https://cds.cern.ch/record/2057379Gluino pair-production matched to parton showers at the next-to-leading order
https://cds.cern.ch/record/2057030
Using a fully automated framework based on the FeynRules and MadGraph5 aMC@NLO programs, we present accurate simulations for gluino pair-production at the LHC. Starting directly from a model Lagrangian that features squark and gluino interactions, event generation is achieved at the next-to-leading order in QCD, matching short-distance events to parton showers and including the subsequent decay of the gluinos. As an application, we study the impact of higher-order corrections in gluino pair-production in a simplified benchmark scenario inspired by current gluino LHC searches.Degrande, CelineFuks, BenjaminHirschi, ValentinProudom, JosselinShao, Hua-ShengMon, 05 Oct 2015 05:40:36 GMT01 Oct 2015arXiv:1510.00391https://cds.cern.ch/record/2057030Intrinsic charm in a matched general-mass scheme
https://cds.cern.ch/record/2056872
The FONLL general-mass variable-flavour number scheme provides a framework for the matching of a calculation in which a heavy quark is treated as a massless parton to one in which the mass dependence is retained throughout. We describe how the usual formulation of FONLL can be extended in such a way that the heavy quark parton distribution functions are freely parameterized at some initial scale, rather than being generated entirely perturbatively. We specifically consider the case of deep-inelastic scattering, in view of applications to PDF determination, and the possible impact of a fitted charm quark distribution on $F_2^c$ is assessed.Ball, Richard DBertone, ValerioBonvini, MarcoForte, StefanoMerrild, Patrick GrothRojo, JuanRottoli, LucaSat, 03 Oct 2015 05:34:30 GMT30 Sep 2015arXiv:1510.00009https://cds.cern.ch/record/2056872Beyond the CMSSM without an Accelerator: Proton Decay and Direct Dark Matter Detection
https://cds.cern.ch/record/2055954
We consider two potential non-accelerator signatures of generalizations of the well-studied constrained minimal supersymmetric standard model (CMSSM). In one generalization, the universality constraints on soft supersymmetry-breaking parameters are applied at some input scale $M_{in}$ below the grand unification (GUT) scale $M_{GUT}$, a scenario referred to as `sub-GUT'. The other generalization we consider is to retain GUT-scale universality for the squark and slepton masses, but to relax universality for the soft supersymmetry-breaking contributions to the masses of the Higgs doublets. As with other CMSSM-like models, the measured Higgs mass requires supersymmetric particle masses near or beyond the TeV scale. Because of these rather heavy sparticle masses, the embedding of these CMSSM-like models in a minimal SU(5) model of grand unification can yield a proton lifetime consistent with current experimental limits, and may be accessible in existing and future proton decay experiments. Another possible signature of these CMSSM-like models is direct detection of supersymmetric dark matter. The direct dark matter scattering rate is typically below the reach of the LUX-ZEPLIN (LZ) experiment if $M_{in}$ is close to $M_{GUT}$, but may lie within its reach if $M_{in} \lesssim 10^{11}$ GeV. Likewise, generalizing the CMSSM to allow non-universal supersymmetry-breaking contributions to the Higgs offers extensive possibilities for models within reach of the LZ experiment that have long proton lifetimes.Ellis, JohnEvans, Jason LLuo, FengNagata, NatsumiOlive, Keith ASandick, PearlWed, 30 Sep 2015 05:59:23 GMT29 Sep 2015arXiv:1509.08838https://cds.cern.ch/record/2055954A note on the fate of the Landau-Yang theorem in non-Abelian gauge theories
https://cds.cern.ch/record/2055393
Using elementary considerations of Lorentz invariance, Bose symmetry and BRST invariance, we argue why the decay of a massive color-octet vector state into a pair of on-shell massless gluons is possible in a non-Abelian SU(N) Yang-Mills theory, we constrain the form of the amplitude of the process and offer a simple understanding of these results in terms of effective-action operators.Cacciari, MatteoDel Debbio, LuigiEspinosa, José RPolosa, Antonio DTesta, MassimoMon, 28 Sep 2015 05:32:07 GMT25 Sep 2015arXiv:1509.07853https://cds.cern.ch/record/2055393Summary of the XXVIIth Rencontres de Blois: Particle Physics and Cosmology
https://cds.cern.ch/record/2055376
This writeup summarises some of the highlights from the 2015 Rencontres de Blois, with a compression ratio of about 100:1 relative to the original presentations.Salam, Gavin PMon, 28 Sep 2015 05:31:10 GMT25 Sep 2015arXiv:1509.07666https://cds.cern.ch/record/2055376$\delta N$ formalism from superpotential and holography
https://cds.cern.ch/record/2055073
We consider the superpotential formalism to describe the evolution of scalar fields during inflation, generalizing it to include the case with non-canonical kinetic terms. We provide a characterization of the attractor behaviour of the background evolution in terms of first and second slow-roll parameters (which need not be small). We find that the superpotential is useful in justifying the separate universe approximation from the gradient expansion, and also in computing the spectra of primordial perturbations around attractor solutions in the $\delta N$ formalism. As an application, we consider a class of models where the background trajectories for the inflaton fields are derived from a product separable superpotential. In the perspective of the holographic inflation scenario, such models are dual to a deformed CFT boundary theory, with $D$ mutually uncorrelated deformation operators. We compute the bulk power spectra of primordial adiabatic and entropy cosmological perturbations, and show that the results agree with the ones obtained by using conformal perturbation theory in the dual picture.Garriga, JaumeUrakawa, YukoVernizzi, FilippoFri, 25 Sep 2015 06:08:02 GMT24 Sep 2015arXiv:1509.07339https://cds.cern.ch/record/2055073Summary and Outlook: 2015 Lepton-Photon Symposium
https://cds.cern.ch/record/2055043
What life is there after Higgs? Specifically, what physics lies beyond the Standard Model (SM)? These are the biggest questions in particle physics today, and my talk is oriented towards efforts to answer them at the LHC and elsewhere.Ellis, JohnFri, 25 Sep 2015 05:44:50 GMT24 Sep 2015arXiv:1509.07336https://cds.cern.ch/record/2055043Introduction to SARAH and related tools
https://cds.cern.ch/record/2054763
I give in this lecture an overview of the features of the Mathematica package SARAH, and explain how it can be used together with other codes to study all aspects of a BSM model. The focus will be on the description of the analytical calculations which SARAH can perform and how this information is used to generate automatically a spectrum generator based on SPheno. I also summarize the main aspects of the other interfaces to public codes like HiggsBounds/HiggsSignals, FeynArts/FormCalc, CalcHep, MicrOmegas, WHIZARD, Vevacious or MadGraph. The appendix contains a short tutorial about the implementation and usage of a new model.Staub, FlorianThu, 24 Sep 2015 06:04:29 GMT21 Sep 2015arXiv:1509.07061https://cds.cern.ch/record/2054763Topological Susceptibility from Slabs
https://cds.cern.ch/record/2054724
In quantum field theories with topological sectors, a non-perturbative quantity of interest is the topological susceptibility chi_t. In principle it seems straightforward to measure chi_t by means of Monte Carlo simulations. However, for local update algorithms and fine lattice spacings, this tends to be difficult, since the Monte Carlo history rarely changes the topological sector. Here we test a method to measure chi_t even if data from only one sector are available. It is based on the topological charges in sub-volumes, which we denote as slabs. Assuming a Gaussian distribution of these charges, this method enables the evaluation of chi_t, as we demonstrate with numerical results for non-linear sigma-models.Bietenholz, Wolfgangde Forcrand, PhilippeGerber, UrsThu, 24 Sep 2015 06:04:13 GMT21 Sep 2015arXiv:1509.06433https://cds.cern.ch/record/2054724QCD corrections to ZZ production in gluon fusion at the LHC
https://cds.cern.ch/record/2054713
We compute the next-to-leading order QCD corrections to the production of two Z-bosons in the annihilation of two gluons at the LHC. Being enhanced by a large gluon flux, these corrections provide distinct and, potentially, the dominant part of the N$^3$LO QCD contributions to Z-pair production in proton collisions. The $gg \to ZZ$ annihilation is a loop-induced process that receives the dominant contribution from loops of five light quarks, that are included in our computation in the massless approximation. We find that QCD corrections increase the $gg \to ZZ$ production cross section by ${\cal O}(50\%-100\%)$ depending on the values of the renormalization and factorization scales used in the leading order computation, and the collider energy. The large corrections to $gg \to ZZ$ channel increase the $pp \to ZZ$ cross section by about six to eight percent, exceeding the estimated theoretical uncertainty of the recent NNLO QCD calculation.Caola, FabrizioMelnikov, KirillRöntsch, RaoulTancredi, LorenzoThu, 24 Sep 2015 06:03:09 GMT22 Sep 2015arXiv:1509.06734https://cds.cern.ch/record/2054713Minimal scalar-less matter-coupled supergravity
https://cds.cern.ch/record/2054304
We build the minimal supergravity model where the nilpotent chiral goldstino superfield is coupled to a chiral matter superfield, realising a different non-linear representation through a mixed nilpotency constraint. The model describes the spontaneous breaking of local supersymmetry in the presence of a generically massive Majorana fermion, but in the absence of elementary scalars. The sign and the size of the cosmological constant, the spectrum and the four-fermion interactions are controlled by suitable parameters.Dall'Agata, GianguidoFerrara, SergioZwirner, FabioTue, 22 Sep 2015 05:52:52 GMT21 Sep 2015arXiv:1509.06345https://cds.cern.ch/record/2054304General squark flavour mixing: constraints, phenomenology and benchmarks
https://cds.cern.ch/record/2053868
We present an extensive study of non-minimal flavour violation in the squark sector in the framework of the Minimal Supersymmetric Standard Model. We investigate the effects of multiple non-vanishing flavour-violating elements in the squark mass matrices by means of a Markov Chain Monte Carlo scanning technique and identify parameter combinations that are favoured by both current data and theoretical constraints. We then detail the resulting distributions of the flavour-conserving and flavour-violating model parameters. Based on this analysis, we propose a set of benchmark scenarios relevant for future studies of non-minimal flavour violation in the Minimal Supersymmetric Standard Model.De Causmaecker, KarenFuks, BenjaminHerrmann, BjoernMahmoudi, FarvahO'Leary, BenPorod, WernerSekmen, SezenStrobbe, NadjaMon, 21 Sep 2015 05:26:33 GMT17 Sep 2015arXiv:1509.05414https://cds.cern.ch/record/2053868Colliding waves on a string in AdS$_3$
https://cds.cern.ch/record/2053557
This paper is concerned with the classical motion of a string in global AdS$_3$. The initially static string stretches between two antipodal points on the boundary circle. Both endpoints are perturbed which creates cusps at a steady rate. The cusps propagate towards the interior where they collide. The behavior of the string depends on the strength of forcing. Three qualitatively different phases can be distinguished: transparent, gray, and black. The transparent region is analogous to a standing wave. In the black phase, there is a horizon on the worldsheet and cusps never reach the other endpoint. The string keeps folding and its length grows linearly over time. In the gray phase, the string still grows linearly. However, cusps do cross to the other side. The transparent and gray regions are separated by a transition point where a logarithmic accumulation of cusps is numerically observed. A simple model reproduces the qualitative behavior of the string in the three phases.Vegh, DavidFri, 18 Sep 2015 06:32:27 GMT16 Sep 2015arXiv:1509.05033https://cds.cern.ch/record/2053557Tools for dark matter indirect detection
https://cds.cern.ch/record/2053365
Cirelli, MarcoFri, 18 Sep 2015 04:06:22 GMT2012https://cds.cern.ch/record/2053365Supersymmetric branes on curved spaces and fluxes
https://cds.cern.ch/record/2051734
We discuss general supersymmetric brane configurations in flux backgrounds of string and M-theory and derive a necessary condition for the worldvolume theory to be supersymmetric on a given curved manifold. This condition resembles very much the conditions found from coupling a supersymmetric field theory to off-shell supergravity but can be derived in any dimension and for up to sixteen supercharges. Apart from the topological twist, all couplings appearing in the supersymmetry condition are linked to fluxes in the bulk. We explicitly derive the condition for D3-, M2- and M5-branes, in which case the results are also useful for constructing holographic duals to the corresponding field theories. In $N=1$ setups we compare the supersymmetry conditions to those that arise by coupling the field theory to off-shell supergravity. We find that the couplings of both old and new minimal supergravity are simultaneously realized, indicating that off-shell supergravity should be coupled via the S-multiplet of 16/16 supergravity in order to describe all supersymmetric brane theories on curved spaces.Triendl, HagenFri, 11 Sep 2015 06:16:13 GMT09 Sep 2015arXiv:1509.02926https://cds.cern.ch/record/2051734Stop-Catalyzed Baryogenesis Beyond the MSSM
https://cds.cern.ch/record/2051712
Non-minimal supersymmetric models that predict a tree-level Higgs mass above the Minimal Supersymmetric Standard Model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside the gauge sector drive the electroweak phase transition.Katz, AndreyPerelstein, MaximRamsey-Musolf, Michael JWinslow, PeterFri, 11 Sep 2015 06:15:49 GMT09 Sep 2015arXiv:1509.02934https://cds.cern.ch/record/2051712The spectrum of anomalous magnetohydrodynamics
https://cds.cern.ch/record/2049627
The equations of anomalous magnetohydrodynamics describe an Abelian plasma where conduction and chiral currents are simultaneously present and constrained by the second law of thermodynamics. At high frequencies the magnetic currents play the leading role and the spectrum is dominated by two-fluid effects. The system behaves instead as a single fluid in the low-frequency regime where the vortical currents induce potentially large hypermagnetic fields. After deriving the physical solutions of the generalized Appleton-Hartree equation, the corresponding dispersion relations are scrutinized and compared with the results valid for cold plasmas. Hypermagnetic knots and fluid vortices can be concurrently present at very low frequencies and suggest a qualitatively different dynamics of the hydromagnetic nonlinearities.Giovannini, MassimoTue, 08 Sep 2015 05:47:52 GMT07 Sep 2015arXiv:1509.02126https://cds.cern.ch/record/2049627Supersymmetry and Inflation
https://cds.cern.ch/record/2049333
Theories with elementary scalar degrees of freedom seem nowadays required for simple descriptions of the Standard Model and of the Early Universe. It is then natural to embed theories of inflation in supergravity, also in view of their possible ultraviolet completion in String Theory. After some general remarks on inflation in supergravity, we describe examples of minimal inflaton dynamics which are compatible with recent observations, including higher-curvature ones inspired by the Starobinsky model. We also discuss different scenarios for supersymmetry breaking during and after inflation, which include a revived role for non-linear realizations. In this spirit, we conclude with a discussion of the link, in four dimensions, between "brane supersymmetry breaking" and the super--Higgs effect in supergravity.Ferrara, SSagnotti, AMon, 07 Sep 2015 06:03:38 GMT04 Sep 2015arXiv:1509.01500https://cds.cern.ch/record/2049333Natural Heavy Supersymmetry
https://cds.cern.ch/record/2048826
We study how, as a result of the scanning of supersymmetry breaking during the cosmological evolution, a relaxation mechanism can naturally determine a hierarchy between the weak scale and the masses of supersymmetric particles. Supersymmetry breaking is determined by QCD instanton effects, in an extremely minimal setup in which a single field drives the relaxation and breaks supersymmetry. Since gauginos are lighter than the other supersymmetric particles by a one-loop factor, the theory is a realisation of Split Supersymmetry free from the naturalness problem.Batell, BrianGiudice, Gian FMcCullough, MatthewThu, 03 Sep 2015 05:57:22 GMT02 Sep 2015arXiv:1509.00834https://cds.cern.ch/record/2048826Generalised universality of gauge thresholds in heterotic vacua with and without supersymmetry
https://cds.cern.ch/record/2048499
We study one-loop quantum corrections to gauge couplings in heterotic vacua with spontaneous supersymmetry breaking. Although in non-supersymmetric constructions these corrections are not protected and are typically model dependent, we show how a universal behaviour of threshold differences, typical of supersymmetric vacua, may still persist. We formulate specific conditions on the way supersymmetry should be broken for this to occur. Our analysis implies a generalised notion of threshold universality even in the case of unbroken supersymmetry, whenever extra charged massless states appear at enhancement points in the bulk of moduli space. Several examples with universality, including non-supersymmetric chiral models in four dimensions, are presented.Angelantonj, CarloFlorakis, IoannisTsulaia, MirianWed, 02 Sep 2015 06:56:32 GMT31 Aug 2015arXiv:1509.00027https://cds.cern.ch/record/2048499Two-Flavor Lattice QCD with a Finite Density of Heavy Quarks: Heavy-Dense Limit and "Particle-Hole" Symmetry
https://cds.cern.ch/record/2048438
We investigate the properties of the half-filling point in lattice QCD (LQCD), in particular the disappearance of the sign problem and the emergence of an apparent particle-hole symmetry, and try to understand where these properties come from by studying the heavy-dense fermion determinant and the corresponding strong-coupling partition function (which can be integrated analytically). We then add in a first step an effective Polyakov loop gauge action (which reproduces the leading terms in the character expansion of the Wilson gauge action) to the heavy-dense partition function and try to analyze how some of the properties of the half-filling point change when leaving the strong coupling limit. In a second step, we take also the leading nearest-neighbor fermion hopping terms into account (including gauge interactions in the fundamental representation) and mention how the method could be improved further to incorporate the full set of nearest-neighbor fermion hoppings. Using our mean-field method, we also obtain an approximate ($\mu$,T) phase diagram for heavy-dense LQCD at finite inverse gauge coupling $\beta$. Finally, we propose a simple criterion to identify the chemical potential beyond which lattice artifacts become dominant.Rindlisbacher, Tobiasde Forcrand, PhilippeWed, 02 Sep 2015 06:55:36 GMT31 Aug 2015arXiv:1509.00087https://cds.cern.ch/record/2048438The Higgs-Yukawa model with higher dimension operators via EMFT
https://cds.cern.ch/record/2048437
Using Extended Mean Field Theory (EMFT) on the lattice, we study properties of the Higgs-Yukawa model as an approximation of the Standard Model Higgs sector, and the effect of higher dimension operators. We note that the discussion of vacuum stability is completely modified in the presence of a $\phi^6$ term, and that the Higgs mass no longer appears fine tuned. We also study the finite temperature transition. Without higher dimension operators the transition is found to be second order (crossover with gauge fields) for the experimental value of the Higgs mass $M_h=125$ GeV. By taking a $\phi^6$ interaction in the Higgs potential as a proxy for a UV completion of the Standard Model, the transition becomes stronger and turns first order if the scale of new physics, i.e. the mass of the lightest mediator particle, is around $1.5$ TeV. This implies that electroweak baryogenesis may be viable in models which introduce new particles around that scale.Akerlund, Oscarde Forcrand, PhilippeWed, 02 Sep 2015 06:55:35 GMT31 Aug 2015arXiv:1508.07959https://cds.cern.ch/record/2048437