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Universality of radiative corrections to gauge couplings for strings with spontaneously broken supersymmetry
https://cds.cern.ch/record/1995142
I review recent work on computing radiative corrections to non-abelian gauge couplings in four-dimensional heterotic vacua with spontaneously broken supersymmetry. The prototype models can be considered as K3 surfaces with additional Scherk-Schwarz fluxes inducing the spontaneous $\mathcal{N}=2 \to \mathcal{N}=0$ breaking. Remarkably, although the gauge thresholds are no longer BPS protected and receive contributions also from the excitations of the RNS sector, their difference is still exactly computable and universal. Based on a talk presented at the DISCRETE 2014 conference at King's College London.Florakis, IoannisSat, 28 Feb 2015 07:51:05 GMThttps://cds.cern.ch/record/1995142Emerging Jets
https://cds.cern.ch/record/1993313
In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilities for discovery at LHCb are also discussed.Schwaller, PedroFri, 20 Feb 2015 08:33:38 GMThttps://cds.cern.ch/record/1993313Towards the physical point hadronic vacuum polarisation from Moebius DWF
https://cds.cern.ch/record/1992983
We present steps towards the computation of the leading-order hadronic contribution to the muon anomalous magnetic moment on RBC/UKQCD physical point DWF ensembles. We discuss several methods for controlling and reducing uncertainties associated to the determination of the HVP form factor.Marinkovic, MarinaThu, 19 Feb 2015 06:53:17 GMThttps://cds.cern.ch/record/1992983Fundamental Composite Electroweak Dynamics: Status at the LHC
https://cds.cern.ch/record/1992768
We determine the current status of the fundamental composite electroweak dynamics paradigm after the discovery of the Higgs boson at the Large Hadron Collider experiments. Our analysis serves as universal and minimal template for a wide class of models with the two limits in parameter space being composite Goldstone Higgs models and Technicolor. This is possible because of the existence of a unified description, both at the effective and fundamental Lagrangian levels, of models of composite Higgs dynamics where the Higgs boson itself can emerge, depending on the way the electroweak symmetry is embedded, either as a pseudo-Goldstone boson or as a massive excitation of the condensate. We constrain the available parameter space at the effective Lagrangian level. We show that a wide class of models of fundamental composite electroweak dynamics, including Technicolor, are compatible with experiments. The results are relevant for future searches of a fundamental composite nature of the Higgs mechanism at the Large Hadron Collider.Arbey, AlexandreWed, 18 Feb 2015 06:43:44 GMThttps://cds.cern.ch/record/1992768Robust collider limits on heavy-mediator Dark Matter
https://cds.cern.ch/record/1992767
We explain how to consistently use Effective Field Theories (EFTs) to set universal bounds on heavy-mediator Dark Matter at colliders, without prejudice on the model underlying a given effective interaction. We illustrate the method for a Majorana fermion, universally coupled to the Standard Model quarks via a dimension-6 axial-axial four-fermion operator. We recast the ATLAS mono-jet analysis and show that a considerable fraction of the parameter space, seemingly excluded by a na\"ive EFT interpretation, is actually still unexplored. Consistently set EFT limits can be reinterpreted in any specific underlying model. We provide two explicit examples for the chosen operator and compare the reach of our model-independent method with that obtainable by dedicated analyses.Racco, DavideWed, 18 Feb 2015 06:43:42 GMThttps://cds.cern.ch/record/1992767Black Hole Solutions in $R^2$ Gravity
https://cds.cern.ch/record/1992512
We find static spherically symmetric solutions of scale invariant $R^2$ gravity. The latter has been shown to be equivalent to General Relativity with a positive cosmological constant and a scalar mode. Therefore, one expects that solutions of the $R^2$ theory will be identical to that of Einstein theory. Indeed, we find that the solutions of $R^2$ gravity are in one-to-one correspondence with solutions of General Relativity in the case of non-vanishing Ricci scalar. However, scalar-flat $R=0$ solutions are global minima of the $R^2$ action and they cannot in general be mapped to solutions of the Einstein theory. As we will discuss, the $R=0$ solutions arise in Einstein gravity as solutions in the tensionless, strong coupling limit $M_P\rightarrow 0$. As a further result, there is no corresponding Birkhoff theorem and the Schwarzschild black hole is by no means unique in this framework. In fact, $R^2$ gravity has a rich structure of vacuum static spherically symmetric solutions partially uncovered here. We also find charged static spherically symmetric backgrounds coupled to a $U(1)$ field. Finally, we provide the entropy and energy formulas for the $R^2$ theory and we find that entropy and energy vanish for scalar-flat backgrounds.Kehagias, AlexTue, 17 Feb 2015 06:33:49 GMThttps://cds.cern.ch/record/1992512$D^6 R^4$ amplitudes in various dimensions
https://cds.cern.ch/record/1989347
Four-graviton couplings in the low energy effective action of type II string vacua compactified on tori are strongly constrained by supersymmetry and U-duality. While the $R^4$ and $D^4 R^4$ couplings are known exactly in terms of Langlands-Eisenstein series of the U-duality group, the $D^6 R^4$ couplings are not nearly as well understood. Exploiting the coincidence of the U-duality group in $D=6$ with the T-duality group in $D=5$, we propose an exact formula for the $D^6 R^4$ couplings in type II string theory compactified on $T^4$, in terms of a genus-two modular integral plus a suitable Eisenstein series. The same modular integral computes the two-loop correction to $D^6 R^4$ in 5 dimensions, but here provides the non-perturbative completion of the known perturbative terms in $D=6$. This proposal hinges on a systematic re-analysis of the weak coupling and large radius of the $D^6 R^4$ in all dimensions $D\geq 3$, which fills in some gaps and resolves some inconsistencies in earlier studies.Pioline, BorisFri, 13 Feb 2015 06:37:29 GMThttps://cds.cern.ch/record/1989347Non-minimally flavour violating dark matter
https://cds.cern.ch/record/1989328
Flavour symmetries provide an appealing mechanism to stabilize the dark matter particle. I present a simple model of quark flavoured dark matter that goes beyond the framework of minimal flavour violation. I discuss the phenomenological implications for direct and indirect dark matter detection experiments, high energy collider searches as well as flavour violating precision data.Blanke, MonikaFri, 13 Feb 2015 06:36:59 GMThttps://cds.cern.ch/record/1989328Generalized Metric Formulation of Double Field Theory on Group Manifolds
https://cds.cern.ch/record/1987944
We rewrite the recently derived cubic action of Double Field Theory on group manifolds [arXiv:1410.6374] in terms of a generalized metric and extrapolate it to all orders in the fields. For the resulting action, we derive the field equations and state them in terms of a generalized curvature scalar and a generalized Ricci tensor. Compared to the generalized metric formulation of DFT derived from tori, all these quantities receive additional contributions related to the non-trivial background. It is shown that the action is invariant under its generalized diffeomorphisms and 2D-diffeomorphisms. Imposing additional constraints relating the background and fluctuations around it, the precise relation between the proposed generalized metric formulation of DFT${}_\mathrm{WZW}$ and of original DFT from tori is clarified. Furthermore we show how to relate DFT${}_\mathrm{WZW}$ of the WZW background with the flux formulation of original DFT.Blumenhagen, RalphTue, 10 Feb 2015 07:07:43 GMThttps://cds.cern.ch/record/1987944Spot the stop with a b-tag
https://cds.cern.ch/record/1987870
The LHC searches for light compressed stop squarks have resulted in considerable bounds in the case where the stop decays to a neutralino and a charm quark. However, in the case where the stop decays to a neutralino, a bottom quark and two fermions via an off-shell W-boson, there is currently a significant unconstrained region in the stop-neutralino mass plane, still allowing for stop masses in the range 90-140 GeV. In this paper we propose a new monojet-like search for light stops, optimized for the four-body decay mode, in which at least one b-tagged jet is required. We show that, already by using the existing 8 TeV LHC data set, such a search would cover the entire unconstrained region. Moreover, in the process of validating our tools against an ATLAS monojet search, we show that the existing limit can be extended to exclude also stop masses below 100 GeV.Ferretti, GabrieleTue, 10 Feb 2015 07:06:43 GMThttps://cds.cern.ch/record/1987870Massive Born--Infeld and Other Dual Pairs
https://cds.cern.ch/record/1987236
We consider massive dual pairs of p-forms and (D-p-1)-forms described by non-linear Lagrangians, where non-linear curvature terms in one theory translate into non-linear mass-like terms in the dual theory. In particular, for D=2p and p even the two non-linear structures coincide when the non-linear massless theory is self-dual. This state of affairs finds a natural realization in the four-dimensional massive N=1 supersymmetric Born-Infeld action, which describes either a massive vector multiplet or a massive linear (tensor) multiplet with a Born-Infeld mass-like term. These systems should play a role for the massive gravitino multiplet obtained from a partial super-Higgs in N=2 Supergravity.Ferrara, SFri, 06 Feb 2015 06:58:50 GMThttps://cds.cern.ch/record/1987236Regge behavior saves String Theory from causality violations
https://cds.cern.ch/record/1985331
Higher-derivative corrections to the Einstein-Hilbert action are present in bosonic string theory leading to the potential causality violations recently pointed out by Camanho et al. We analyze in detail this question by considering high-energy string-brane collisions at impact parameters $b \le l_s$ (the string-length parameter) with $l_s \gg R_p$ (the characteristic scale of the D$p$-brane geometry). If we keep only the contribution of the massless states causality is violated for a set of initial states whose polarization is suitably chosen with respect to the impact parameter vector. Such violations are instead neatly avoided when the full structure of string theory - and in particular its Regge behavior - is taken into account.D'Appollonio, GiuseppeThu, 05 Feb 2015 06:38:16 GMThttps://cds.cern.ch/record/1985331Threshold corrections, generalised prepotentials and Eichler integrals
https://cds.cern.ch/record/1984735
We continue our study of one-loop integrals associated to BPS-saturated amplitudes in $\mathcal{N}=2$ heterotic vacua. We compute their large-volume behaviour, and express them as Fourier series in the complexified volume, with Fourier coefficients given in terms of Niebur-Poincar\'e series in the complex structure modulus. The closure of Niebur-Poincar\'e series under modular derivatives implies that such integrals derive from holomorphic prepotentials $f_n$, generalising the familiar prepotential of $\mathcal{N}=2$ supergravity. These holomorphic prepotentials transform anomalously under T-duality, in a way characteristic of Eichler integrals. We use this observation to compute their quantum monodromies under the duality group. We extend the analysis to modular integrals with respect to Hecke congruence subgroups, which naturally arise in compactifications on non-factorisable tori and freely-acting orbifolds. In this case, we derive new explicit results including closed-form expressions for integrals involving the ${\varGamma}_0(N)$ Hauptmodul, a full characterisation of holomorphic prepotentials including their quantum monodromies, as well as concrete formulae for holomorphic Yukawa couplings.Angelantonj, CarloWed, 04 Feb 2015 06:35:35 GMThttps://cds.cern.ch/record/1984735Natural Quasi-Alignment with two Higgs Doublets and RGE Stability
https://cds.cern.ch/record/1983877
In the context of two Higgs doublet models, we study the conditions required in order to have stable quasi-alignment in flavour space. We show that stability under the RGE imposes strong constraints on the flavour structure of the Yukawa couplings associated to each one of the Higgs doublets. In particular, we find a novel solution, where all Yukawa couplings are proportional to the so-called democratic matrix. This solution is rather unique, since it is the only stable solution which is a good starting point for reproducing the observed pattern of quark masses and mixing. We also show that this stable solution can be obtained by imposing on the Lagrangian a $Z_3 \times Z^\prime_3$ flavour symmetry. Quark masses of the lighter quark generations are generated through the breaking of this discrete symmetry, and, at this stage, scalar mediated FCNC arise, but are naturally suppressed by the smallness of light quark masses. In this way, we relate Higgs alignment to the hierarchy of quark masses through a discrete family symmetry.Botella, F JFri, 30 Jan 2015 07:57:45 GMThttps://cds.cern.ch/record/1983877The Flavour Portal to Dark Matter
https://cds.cern.ch/record/1983871
We present a class of models in which dark matter (DM) is a fermionic singlet under the Standard Model (SM) gauge group but is charged under a symmetry of flavour that acts as well on the SM fermions. Interactions between DM and SM particles are mediated by the scalar fields that spontaneously break the flavour symmetry, the so-called flavons. In the case of gauged flavour symmetries, the interactions are also mediated by the flavour gauge bosons. We first discuss the construction and the generic features of this class of models. Then a concrete example with an abelian flavour symmetry is considered. We compute the complementary constraints from the relic abundance, direct detection experiments and flavour observables, showing that wide portions of the parameter space are still viable. Other possibilities like non-abelian flavour symmetries can be analysed within the same framework.Calibbi, LorenzoFri, 30 Jan 2015 07:57:45 GMThttps://cds.cern.ch/record/1983871Higgs boson decay into b-quarks at NNLO accuracy
https://cds.cern.ch/record/1983867
We compute the fully differential decay rate of the Standard Model Higgs boson into b-quarks at next-to-next-to-leading order (NNLO) accuracy in alpha_S. We employ a general subtraction scheme developed for the calculation of higher order perturbative corrections to QCD jet cross sections, which is based on the universal infrared factorization properties of QCD squared matrix elements. We show that the subtractions render the various contributions to the NNLO correction finite. In particular, we demonstrate analytically that the sum of integrated subtraction terms correctly reproduces the infrared poles of the two-loop double virtual contribution to this process. We present illustrative differential distributions obtained by implementing the method in a parton level Monte Carlo program. The basic ingredients of our subtraction scheme, used here for the first time to compute a physical observable, are universal and can be employed for the computation of more involved processes.Del Duca, VittorioFri, 30 Jan 2015 07:57:44 GMThttps://cds.cern.ch/record/1983867Naturalness in the Dark at the LHC
https://cds.cern.ch/record/1982747
We revisit the Twin Higgs scenario as a "dark" solution to the little hierarchy problem, identify the structure of a minimal model and its viable parameter space, and analyze its collider implications. In this model, dark naturalness generally leads to Hidden Valley phenomenology. The twin particles, including the top partner, are all Standard-Model-neutral, but naturalness favors the existence of twin strong interactions -- an asymptotically-free force that confines not far above the Standard Model QCD scale -- and a Higgs portal interaction. We show that, taken together, these typically give rise to exotic decays of the Higgs to twin hadrons. Across a substantial portion of the parameter space, certain twin hadrons have visible and often displaced decays, providing a potentially striking LHC signature. We briefly discuss appropriate experimental search strategies.Craig, NathanielFri, 23 Jan 2015 07:09:59 GMThttps://cds.cern.ch/record/1982747Discrete Glimpses of the Physics Landscape after the Higgs Discovery
https://cds.cern.ch/record/1982737
What is the Higgs boson telling us? What else is there? How do we find it? This talk discusses these current topics in particle physics in the wake of the Higgs discovery, with particular emphasis on the discrete symmetries CP and R-parity, not forgetting flavour physics and dark matter, and finishing with some remarks about possible future colliders.Ellis, JohnFri, 23 Jan 2015 07:08:53 GMThttps://cds.cern.ch/record/1982737Neutrino versus antineutrino cross sections and CP violation
https://cds.cern.ch/record/1981097
We discuss the nuclear interactions of neutrinos versus those of antineutrinos, a relevant comparison for CP violation experiments in the neutrino sector. We consider the MiniBooNE quasielastic-like double differential neutrinos and antineutrinos cross sections which are flux dependent and hence specific to the MiniBooNE set-up. We combine them introducing their sum and their difference. We show that the last combination can bring a general information, which can be exploited in other experiments, on the nuclear matrix elements of the axial vector interference term. Our theoretical model reproduces well the two cross sections combinations. This confirms the need for a sizeable multinucleon component in particular in the interference term.Ericson, MWed, 14 Jan 2015 06:26:23 GMThttps://cds.cern.ch/record/1981097Wall-crossing made smooth
https://cds.cern.ch/record/1980359
In $D=4,N=2$ theories on $R^{3,1}$, the index receives contributions not only from single-particle BPS states, counted by the BPS indices, but also from multi-particle states made of BPS constituents. In a recent work [arXiv:1406.2360], a general formula expressing the index in terms of the BPS indices was proposed, which is smooth across walls of marginal stability and reproduces the expected single-particle contributions. In this note, I analyze the two-particle contributions predicted by this formula, and show agreement with the spectral asymmetry of the continuum of scattering states in the supersymmetric quantum mechanics of two non-relativistic, mutually non-local dyons. This provides a physical justification for the error function profile used in the mathematics literature on indefinite theta series, and in the physics literature on black hole partition functions.Pioline, BorisFri, 09 Jan 2015 07:08:58 GMThttps://cds.cern.ch/record/1980359Explaining $h\to\mu^\pm\tau^\mp$, $B\to K^* \mu^+\mu^-$ and $B\to K \mu^+\mu^-/B\to K e^+e^-$ in a two-Higgs-doublet model with gauged $L_\mu-L_\tau$
https://cds.cern.ch/record/1980012
The LHC observed so far three deviations from the Standard Model (SM) predictions in flavour observables: LHCb reported anomalies in $B\to K^* \mu^+\mu^-$ and $R(K)=B\to K \mu^+\mu^-/B\to K e^+e^-$ while CMS found an excess in $h\to\mu\tau$. We show, for the first time, how these deviations from the SM can be explained within a single well-motivated model: a two-Higgs-doublet model with gauged $L_\mu-L_\tau$ symmetry. We find that, despite the constraints from $\tau\to\mu\mu\mu$ and $B_s$--$\overline{B}_s$ mixing, one can explain $h \to\mu\tau$, $B\to K^* \mu^+\mu^-$ and $R(K)$ simultaneously, obtaining interesting correlations among the observables.Crivellin, AndreasWed, 07 Jan 2015 08:01:17 GMThttps://cds.cern.ch/record/1980012LHC constraints on gauge boson couplings to dark matter
https://cds.cern.ch/record/1979702
Collider searches for energetic particles recoiling against missing transverse energy allow to place strong bounds on the interactions between dark matter (DM) and standard model particles. In this article we update and extend LHC constraints on effective dimension-7 operators involving DM and electroweak gauge bosons. A concise comparison of the sensitivity of the mono-photon, mono-W, mono-Z, mono-W/Z, invisible Higgs-boson decays in the vector boson fusion mode and the mono-jet channel is presented. Depending on the parameter choices, either the mono-photon or the mono-jet data provide the most stringent bounds at the moment. We furthermore explore the potential of improving the current 8 TeV limits at 14 TeV. Future strategies capable of disentangling the effects of the different effective operators involving electroweak gauge bosons are discussed as well.Crivellin, AndreasTue, 06 Jan 2015 06:25:40 GMThttps://cds.cern.ch/record/1979702Correlation functions of the chiral stress-tensor multiplet in N=4 SYM
https://cds.cern.ch/record/1979332
We give a new method for computing the correlation functions of the chiral part of the stress-tensor supermultiplet that relies on the reformulation of N=4 SYM in twistor space. It yields the correlation functions in the Born approximation as a sum of Feynman diagrams on twistor space that involve only propagators and no integration vertices. We use this unusual feature of the twistor Feynman rules to compute the correlation functions in terms of simple building blocks which we identify as a new class of N=4 off-shell superconformal invariants. Making use of the duality between correlation functions and planar scattering amplitudes, we demonstrate that these invariants represent an off-shell generalisation of the on-shell invariants defining tree-level scattering amplitudes in N=4 SYM.Chicherin, DmitryWed, 31 Dec 2014 07:02:10 GMThttps://cds.cern.ch/record/1979332Observable Effects of General New Scalar Particles
https://cds.cern.ch/record/1979299
We classify all possible new scalar particles that can have renormalizable linear couplings to Standard Model fields and therefore be singly produced at colliders. We show that this classification exhausts the list of heavy scalar particles that contribute at the tree level to the Standard Model effective Lagrangian to dimension six. We compute this effective Lagrangian for a general scenario with an arbitrary number of new scalar particles and obtain flavor-preserving constraints on their couplings and masses. This completes the tree-level matching of the coefficients of dimension five and six operators in the effective Lagrangian to arbitrary extensions of the Standard Model.de Blas, JorgeWed, 31 Dec 2014 07:01:44 GMThttps://cds.cern.ch/record/1979299Automated NNLL+NLO Resummation for Jet-Veto Cross Sections
https://cds.cern.ch/record/1979152
In electroweak-boson production processes with a jet veto, higher-order corrections are enhanced by logarithms of the veto scale over the invariant mass of the boson system. In this paper, we resum these Sudakov logarithms at next-to-next-to-leading logarithmic (NNLL) accuracy and match our predictions to next-to-leading order (NLO) fixed-order results. We perform the calculation in an automated way, for arbitrary electroweak final states and in the presence of kinematic cuts on the leptons produced in the decays of the electroweak bosons. The resummation is based on a factorization theorem for the cross sections into hard functions, which encode the virtual corrections to the boson production process, and beam functions, which describe the low-p_T emissions collinear to the beams. The one-loop hard functions for arbitrary processes are calculated using the MadGraph5_aMC@NLO framework, while the beam functions are process independent. We perform the resummation for a variety of processes, in particular for W+W- pair production followed by leptonic decays of the W bosons.Becher, ThomasTue, 30 Dec 2014 06:25:03 GMThttps://cds.cern.ch/record/1979152