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The moduli space of instantons on an ALE space from 3d $\mathcal{N}=4$ field theories
http://cds.cern.ch/record/2047576
The moduli space of instantons on an ALE space is studied using the moduli space of $\mathcal{N}=4$ field theories in three dimensions. For instantons in a simple gauge group $G$ on $\mathbb{C}^2/\mathbb{Z}_n$, the Hilbert series of such an instanton moduli space is computed from the Coulomb branch of the quiver given by the affine Dynkin diagram of $G$ with flavour nodes of unitary groups attached to various nodes of the Dynkin diagram. We provide a simple prescription to determine the ranks and the positions of these flavour nodes from the order of the orbifold $n$ and from the residual subgroup of $G$ that is left unbroken by the monodromy of the gauge field at infinity. For $G$ a simply laced group of type $A$, $D$ or $E$, the Higgs branch of such a quiver describes the moduli space of $SU(n)$ instantons on orbifold $\mathbb{C}^2/\widehat{G}$, where $\widehat{G}$ is the discrete group that is in McKay correspondence to $G$. Moreover, we present the quiver whose Coulomb branch is the moduli space of $SO(2N)$ instantons on a smooth ALE space of type $A_{2n-1}$ with a certain monodromy of the gauge field at infinity. The Higgs branch of such a quiver is conjectured to be the moduli space of $SU(2n)$ instantons on a smooth ALE space of type $D_{N}$.Mekareeya, NoppadolFri, 28 Aug 2015 05:52:49 GMT27 Aug 2015arXiv:1508.06813http://cds.cern.ch/record/2047576The broken string in anti-de Sitter space
http://cds.cern.ch/record/2047567
This paper describes an efficient method for solving the classical string equations of motion in (2+1)-dimensional anti-de Sitter spacetime. Exact string solutions are identified that are the analogs of piecewise linear strings in flat space. They can be used to approximate any smooth string motion to arbitrary accuracy. Cusps on the string move with the speed of light and their collisions are described by a Picard-Lefschetz-type formula. Explicit examples are shown with the string ending on two boundary quarks. The technique is ideally suited for numerical simulations. A Mathematica notebook that has been used to generate the relevant figures is also included.Vegh, DavidFri, 28 Aug 2015 05:52:44 GMT26 Aug 2015arXiv:1508.06637http://cds.cern.ch/record/2047567Prospects and status of quark mass renormalization in three-flavour QCD
http://cds.cern.ch/record/2047554
We present the current status of a revised strategy to compute the running of renormalized quark masses in QCD with three flavours of massless O(a) improved Wilson quarks. The strategy employed uses the standard finite-size scaling method in the Schr\"odinger functional and accommodates for the non-perturbative scheme-switch which becomes necessary at intermediate renormalized couplings as discussed in [arXiv:1411.7648].Campos, IFritzsch, PPena, CPreti, DRamos, AVladikas, AFri, 28 Aug 2015 05:52:11 GMT27 Aug 2015arXiv:1508.06939http://cds.cern.ch/record/2047554Phenomenological aspects of flavoured dark matter
http://cds.cern.ch/record/2047242
Flavour symmetries in the dark sector are a theoretically motivated and phenomenologically appealing concept. The dark matter particle can be stabilised with the help of flavour symmetries, without the need to introduce an additional discrete symmetry by hand. Apart from the usual searches in direct and indirect detection experiments and high energy colliders, flavoured dark matter generally also gives rise to new flavour violating interactions leading to interesting signatures in rare meson decays. This proceedings article reviews a simplified model of flavoured dark matter in which the dark matter coupling to quarks constitutes a new source of flavour violation, so that the model goes beyond Minimal Flavour Violation. Particular emphasis is put on the discussion of its phenomenological implications in flavour, collider and direct detection experiments.Blanke, MonikaThu, 27 Aug 2015 05:55:34 GMT25 Aug 2015arXiv:1508.06179http://cds.cern.ch/record/2047242Indirect determinations of the top quark mass
http://cds.cern.ch/record/2046611
We give a complete analysis of indirect determinations of the top quark mass in the Standard Model by introducing a systematic procedure to identify observables that receive quantum corrections enhanced by powers of $M_t$. We propose to use flavour physics as a tool to extract the top quark mass. Although present data give only a poor determination, we show how future theoretical and experimental progress in flavour physics can lead to an accuracy in $M_t$ well below 2 GeV. We revisit determinations of $M_t$ from electroweak data, showing how an improved measurement of the $W$ mass leads to an accuracy well below 1 GeV.Giudice, Gian FParadisi, ParideStrumia, AlessandroTue, 25 Aug 2015 05:57:51 GMT21 Aug 2015arXiv:1508.05332http://cds.cern.ch/record/2046611Symanzik improvement of the gradient flow in lattice gauge theories
http://cds.cern.ch/record/2046593
We apply the Symanzik improvement programme to the 4+1-dimensional local re-formulation of the gradient flow in pure $SU(N)$ lattice gauge theories. We show that the classical nature of the flow equation allows to eliminate all cutoff effects at $\mathcal O(a^2)$ which originate either from the discretized gradient flow equation or from the gradient flow observable. All the remaining $\mathcal O(a^2)$ effects can be understood in terms of local counterterms at the zero flow time boundary. We classify these counterterms and provide a complete set as required for on-shell improvement. Compared to the 4-dimensional pure gauge theory only a single additional counterterm is required, which corresponds to a modified initial condition for the flow equation. A consistency test in perturbation theory is passed and allows to determine all counterterm coefficients to lowest non-trivial order in the coupling.Ramos, ASint, STue, 25 Aug 2015 05:57:41 GMT22 Aug 2015arXiv:1508.05552http://cds.cern.ch/record/2046593Simplified dark matter top-quark interactions at the LHC
http://cds.cern.ch/record/2045960
Stringent limits on the interactions between dark matter (DM) and the standard model can be set by studying how initial-state or final-state particles recoil against missing transverse energy (MET). In this work, we improve, extend and correct LHC constraints on the interactions between DM and top quarks that are mediated by the exchange of spin-0 s-channel resonances. A comparison of the LHC run-1 sensitivity of the two main search channels is presented, which shows that mono-jet searches are typically more restrictive than the MET + tbar t searches. We furthermore explore the reach of the 14 TeV LHC. The collider constraints are compared to the restrictions arising from direct and indirect detection as well as the DM relic abundance, and we also reflect on effective field theory interpretations of the LHC exclusions.Haisch, UlrichRe, EmanueleFri, 21 Aug 2015 06:20:46 GMT02 Mar 2015arXiv:1503.00691http://cds.cern.ch/record/2045960Neutron star structure from QCD
http://cds.cern.ch/record/2045940
In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.Fraga, Eduardo SKurkela, AleksiVuorinen, AleksiFri, 21 Aug 2015 06:19:38 GMT20 Aug 2015arXiv:1508.05019http://cds.cern.ch/record/2045940On a Canonical Quantization of 3D Anti de Sitter Pure Gravity
http://cds.cern.ch/record/2045167
We perform a canonical quantization of pure gravity on AdS3 using as a technical tool its equivalence at the classical level with a Chern-Simons theory with gauge group SL(2,R)xSL(2,R). We first quantize the theory canonically on an asymptotically AdS space --which is topologically the real line times a Riemann surface with one connected boundary. Using the "constrain first" approach we reduce canonical quantization to quantization of orbits of the Virasoro group and Kaehler quantization of Teichmuller space. After explicitly computing the Kaehler form for the torus with one boundary component and after extending that result to higher genus, we recover known results, such as that wave functions of SL(2,R) Chern-Simons theory are conformal blocks. We find new restrictions on the Hilbert space of pure gravity by imposing invariance under large diffeomorphisms and normalizability of the wave function. The Hilbert space of pure gravity is shown to be the target space of Conformal Field Theories with continuous spectrum and a lower bound on operator dimensions. A projection defined by topology changing amplitudes in Euclidean gravity is proposed. It defines an invariant subspace that allows for a dual interpretation in terms of a Liouville CFT. Problems and features of the CFT dual are assessed and a new definition of the Hilbert space, exempt from those problems, is proposed in the case of highly-curved AdS3.Kim, JihunPorrati, MassimoTue, 18 Aug 2015 05:50:57 GMT14 Aug 2015arXiv:1508.03638http://cds.cern.ch/record/2045167Higgs-bosons couplings to quarks and leptons in the supersymmetric Standard Model with a gauge singlet
http://cds.cern.ch/record/2043296
The loop corrections to the couplings of Higgs bosons to quarks and charged leptons are calculated within supersymmetric versions of the Standard Model, extended by a gauge singlet. The effective couplings of the $SU(2)_L$ doublet and singlet Higgs bosons to quarks and leptons, induced by sfermion loops, are derived. Analytic expressions for the case of generic sfermion flavour mixing, including the complete resummation of all chirally-enhanced contributions are presented. These results are important in scenarios in which the mixing between singlet and doublet components of Higgs bosons is small, and the (pseudo) scalar component of the doublet is light. The calculated loop effects can have important consequences in flavour physics, especially for $\Delta F=2$ processes.Crivellin, AndreasYamada, YouichiThu, 13 Aug 2015 05:43:57 GMT12 Aug 2015arXiv:1508.02855http://cds.cern.ch/record/2043296Fiducial cross sections for Higgs boson production in association with a jet at next-to-next-to-leading order in QCD
http://cds.cern.ch/record/2042406
We extend the recent computation of Higgs boson production in association with a jet through next-to-next-to-leading order in perturbative QCD by including decays of the Higgs boson to electroweak vector bosons. This allows us to compute fiducial cross sections and kinematic distributions including realistic selection criteria for the Higgs boson decay products. As an illustration, we present results for $pp \to H + j \to \gamma \gamma + j$ closely following the ATLAS 8 TeV analysis and for $pp \to H+ j \to W W + j \to e^+ \mu^- \nu \bar \nu + j $ in a CMS-like 13 TeV setup.Caola, FabrizioMelnikov, KirillSchulze, MarkusWed, 12 Aug 2015 05:55:30 GMT11 Aug 2015arXiv:1508.02684http://cds.cern.ch/record/2042406Probing the Moduli Dependence of Refined Topological Amplitudes
http://cds.cern.ch/record/2041125
With the aim of providing a worldsheet description of the refined topological string, we continue the study of a particular class of higher derivative couplings $F_{g,n}$ in the type II string effective action compactified on a Calabi-Yau threefold. We analyse first order differential equations in the anti-holomorphic moduli of the theory, which relate the $F_{g,n}$ to other component couplings. From the point of view of the topological theory, these equations describe the contribution of non-physical states to twisted correlation functions and encode an obstruction for interpreting the $F_{g,n}$ as the free energy of the refined topological string theory. We investigate possibilities of lifting this obstruction by formulating conditions on the moduli dependence under which the differential equations simplify and take the form of generalised holomorphic anomaly equations. We further test this approach against explicit calculations in the dual heterotic theory.Antoniadis, IgnatiosFlorakis, IoannisHohenegger, StefanNarain, K SAssi, Ahmad ZeinFri, 07 Aug 2015 07:00:09 GMT06 Aug 2015arXiv:1508.01477http://cds.cern.ch/record/2041125Putting a Stop to di-Higgs Modifications
http://cds.cern.ch/record/2041064
Pair production of Higgs bosons at hadron colliders is an enticing channel to search for new physics. New colored particles that couple strongly to the Higgs, such as those most often called upon to address the hierarchy problem, provide well motivated examples in which large enhancements of the di-Higgs rate are possible, at least in principle. However, in such scenarios the di-Higgs production rate is tightly correlated with the single Higgs production rate and, since the latter is observed to be SM-like, one generally expects that only modest enhancements in di-Higgs production are allowed by the LHC Run 1 data. We examine the contribution of top squarks (stops) in a simplified supersymmetry model to di-Higgs production and find that this general expectation is indeed borne out. In particular, the allowed deviations are typically small, but there are tuned regions of parameter space where expectations based on EFT arguments break down in which order 100% enhancements to the di-Higgs production rate are possible and are simultaneously consistent with the observed single Higgs production rates. These effects are potentially observable with the high luminosity run of the LHC or at a future hadron collider.Batell, BrianMcCullough, MatthewStolarski, DanielVerhaaren, Christopher BFri, 07 Aug 2015 06:58:23 GMT05 Aug 2015arXiv:1508.01208http://cds.cern.ch/record/2041064Supersymmetric Dark Matter after LHC Run 1
http://cds.cern.ch/record/2040986
Different mechanisms operate in various regions of the MSSM parameter space to bring the relic density of the lightest neutralino, neutralino_1, assumed here to be the LSP and thus the Dark Matter (DM) particle, into the range allowed by astrophysics and cosmology. These mechanisms include coannihilation with some nearly-degenerate next-to-lightest supersymmetric particle (NLSP) such as the lighter stau (stau_1), stop (stop_1) or chargino (chargino_1), resonant annihilation via direct-channel heavy Higgs bosons H/A, the light Higgs boson h or the Z boson, and enhanced annihilation via a larger Higgsino component of the LSP in the focus-point region. These mechanisms typically select lower-dimensional subspaces in MSSM scenarios such as the CMSSM, NUHM1, NUHM2 and pMSSM10. We analyze how future LHC and direct DM searches can complement each other in the exploration of the different DM mechanisms within these scenarios. We find that the stau_1 coannihilation regions of the CMSSM, NUHM1, NUHM2 can largely be explored at the LHC via searches for missing E_T events and long-lived charged particles, whereas their H/A funnel, focus-point and chargino_1 coannihilation regions can largely be explored by the LZ and Darwin DM direct detection experiments. We find that the dominant DM mechanism in our pMSSM10 analysis is chargino_1 coannihilation: {parts of its parameter space can be explored by the LHC, and a larger portion by future direct DM searches.Bagnaschi, E ABuchmueller, OCavanaugh, RCitron, MDe Roeck, ADolan, M JEllis, J RFlaecher, HHeinemeyer, SIsidori, GMalik, SSantos, D MartinezOlive, K ASakurai, Kde Vries, K JWeiglein, GFri, 07 Aug 2015 06:13:06 GMT05 Aug 2015arXiv:1508.01173http://cds.cern.ch/record/2040986EFT for Vortices with Dilaton-dependent Localized Flux
http://cds.cern.ch/record/2040415
We study how codimension-two objects like vortices back-react gravitationally with their environment in theories (such as 4D or higher-dimensional supergravity) where the bulk is described by a dilaton-Maxwell-Einstein system. We do so both in the full theory, for which the vortex is an explicit classical `fat brane' solution, and in the effective theory of `point branes' appropriate when the vortices are much smaller than the scales of interest for their back-reaction (such as the transverse Kaluza-Klein scale). We extend the standard Nambu-Goto description to include the physics of flux-localization wherein the ambient flux of the external Maxwell field becomes partially localized to the vortex, generalizing the results of a companion paper to include dilaton-dependence for the tension and localized flux. In the effective theory, such flux-localization is described by the next-to-leading effective interaction, and the boundary conditions to which it gives rise are known to play an important role in how (and whether) the vortex causes supersymmetry to break in the bulk. We track how both tension and localized flux determine the curvature of the space-filling dimensions. Our calculations provide the tools required for computing how scale-breaking vortex interactions can stabilize the extra-dimensional size by lifting the dilaton's flat direction. For small vortices we derive a simple relation between the near-vortex boundary conditions of bulk fields as a function of the tension and localized flux in the vortex action that provides the most efficient means for calculating how physical vortices mutually interact without requiring a complete construction of their internal structure. In passing we show why a common procedure for doing so using a $\delta$-function can lead to incorrect results. Our procedures generalize straightforwardly to general co-dimension objects.Burgess, C PDiener, RossWilliams, MWed, 05 Aug 2015 06:27:24 GMT04 Aug 2015arXiv:1508.00856http://cds.cern.ch/record/2040415Soft Pomeron in Holographic QCD
http://cds.cern.ch/record/2040356
We study the graviton Regge trajectory in Holographic QCD as a model for high energy scattering processes dominated by soft pomeron exchange. This is done by considering spin J fields from the closed string sector that are dual to glueball states of even spin and parity. In particular, we construct a model that governs the analytic continuation of the spin J field equation to the region of real J < 2, which includes the scattering domain of negative Maldelstam variable t. The model leads to approximately linear Regge trajectories and is compatible with the measured values of 1.08 for the intercept and 0.25 GeV$^{-2}$ for the slope of the soft pomeron. The intercept of the secondary pomeron trajectory is in the same region of the subleading trajectories, made of mesons, proposed by Donnachie and Landshoff, and should therefore be taken into account.Ballon-Bayona, AlfonsoQuevedo, Robert CarcassésCosta, Miguel SDjurić, MarkoWed, 05 Aug 2015 06:26:32 GMT31 Jul 2015arXiv:1508.00008http://cds.cern.ch/record/2040356A manifestly scale-invariant regularization and quantum effective operators
http://cds.cern.ch/record/2040326
Scale invariant theories are often used to address the hierarchy problem, but the regularization of their quantum corrections introduces a dimensionful coupling (dimensional regularization) or scale (Pauli-Villars, etc) which breaks this symmetry explicitly. We avoid this problem and study the implications of a manifestly scale invariant regularization in (classically) scale invariant theories. To this end, we use a dilaton-dependent subtraction function $\mu=\mu(\sigma)$ and spontaneous breaking of scale symmetry that generate the usual subtraction scale. One consequence is the emergence of a new quantum correction $\Delta U(\phi,\sigma)$ to the one-loop scalar potential for $\phi$, beyond that of Coleman-Weinberg. $\Delta U$ is generated as a finite one-loop effect from an otherwise "evanescent" contribution to the field-dependent masses when these multiply the singularities of the one-loop integral. $\Delta U$ contains higher dimensional effective operators and is independent of the subtraction dimensionless parameter. While $\Delta U$ vanishes on the tree-level ground state, a small (quantum) fluctuation from the critical point renders the potential unstable. For other $\mu=\mu(\phi,\sigma)$, quantum (effective) interactions between the visible sector (of the higgs scalar $\phi$) and the hidden sector (dilaton $\sigma$) remain present in their classical decoupling limit, but vanish at large $\langle\sigma\rangle$.Ghilencea, D MWed, 05 Aug 2015 06:24:37 GMT03 Aug 2015arXiv:1508.00595http://cds.cern.ch/record/2040326Relaxing the Electroweak Scale: the Role of Broken dS Symmetry
http://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:1507.08649http://cds.cern.ch/record/2039436Global Parton Distributions for the LHC Run II
http://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:1507.07891http://cds.cern.ch/record/2038936A perturbed lepton-specific two-Higgs-doublet model facing experimental hints for physics beyond the Standard Model
http://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:1507.07567http://cds.cern.ch/record/2038929Lorentz violation in gravity
http://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:1507.07687http://cds.cern.ch/record/2038911Lepton Flavour Violating top decays at the LHC
http://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:1507.07163http://cds.cern.ch/record/2038308Heavy Vector Partners of the Light Composite Higgs
http://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:1507.07102http://cds.cern.ch/record/2038290Large scale structure from viscous dark matter
http://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:1507.06665http://cds.cern.ch/record/2037741Quark flavour observables in the Littlest Higgs model with T-parity after LHC Run 1
http://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:1507.06316http://cds.cern.ch/record/2037504