arXiv subjects

Valentin V. Khoze

Publications and source records attributed to Valentin V. Khoze.

At least 73 records · Page 4Linked to original sources

arXiv2011

RG Invariants, Unification and the Role of the Messenger Scale in General Gauge Mediation

In General Gauge Mediation (GGM) all MSSM soft sfermion masses at a high scale M_mess can be parameterised by three a priori independent scales Λ_{S;1,2,3}(M_mess). (Similarly the gaugino masses are given by Λ_{G;1,2,3}(M_mess).) For the first two generations this parameterisation in terms of a set of running Λ_{S;1,2,3}(μ) -- conveniently obtained from appropriate RG invariants -- continues to hold all the way down to the electroweak scale. This is not the case for the third generation because of the large Yukawa couplings. Together these two observations imply that the messenger scale is an additional parameter of GGM models. In models where all messengers are in complete GUT multiplets (without significant mass splittings), all Λ_{S,r} are equal at M_mess. Starting from the observable mass spectrum at the electroweak scale we present a strategy to determine if this unification occurs and at which scale. This approach uses data accessible at colliders to gain insight into high scale unification physics beyond the unification of gauge couplings.

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arXiv2011

Mass Sum Rules and the Role of the Messenger Scale in General Gauge Mediation

In General Gauge Mediation (GGM), supersymmetry breaking is communicated to the Standard Model (MSSM) sector via gauge interactions at a high scale which we refer to as the messenger scale. At this scale GGM predicts certain sum rules between the MSSM sfermion masses. We investigate the validity and the ultimate fate of these sum rules after RG evolution down to the electroweak scale where the mass spectrum will be probed at colliders. We find that the sum rules hold for the first two generations. However the third generation (where sfermions are lightest) violates one of the two sum rules by 10 to 50% over the explored parameter space. This constrains and quantifies the potential use of sum rules as a signature of gauge mediation. We also comment on the role played by the messenger scale in single- and multi-scale GGM models.

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arXiv2010

Pure General Gauge Mediation for Early LHC Searches

We present benchmark points for Pure General Gauge Mediation (GGM) models specifically optimised for early LHC searches. The pure GGM set-up is as defined in our previous paper arXiv:0910.2674: namely we adopt the minimal set-up in which B_mu is generated only through gauge interactions, and as a result tan beta is a prediction rather than an input. The only input parameters are messenger masses together with two independent scales which generate gaugino and scalar masses. The parameter space favoured by current experimental data includes an interesting region with light gluinos (m_g < 500 GeV and relatively heavy squarks) and a bino-like NLSP where early discovery is likely. We also find interesting regions of parameter space where the NLSP is a stau or stau/neutralino co-NLSP and the squark masses are relatively low. We present benchmark points which are typical for each of these three regions, and give the spectrum, branching ratios, and also the overall 2 -> 2 cross-sections. This data in SLHA format can be found at http://www.ippp.dur.ac.uk/~SUSY

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arXiv2010

Analytic Results for MHV Wilson Loops

We obtain concise analytic formulae for Wilson loops computed on special n-point polygonal contours through two-loops in weakly coupled N=4 supersymmetric gauge theory. The contours we consider can be embedded into a (1+1)-dimensional subspace of the 4-dimensional gauge theory, corresponding to the boundary of the AdS_3 on the string theory side. Our analytic results hold for any number of edges, thus generalising to arbitrary n the recently derived expressions for 2-dimensional octagons. These polygonal Wilson loops have been conjectured to be equivalent to MHV scattering amplitudes in planar N=4 SYM.

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arXiv2010

Simplicity of Polygon Wilson Loops in N=4 SYM

Wilson loops with lightlike polygonal contours have been conjectured to be equivalent to MHV scattering amplitudes in N=4 super Yang-Mills. We compute such Wilson loops for special polygonal contours at two loops in perturbation theory. Specifically, we concentrate on the remainder function R, obtained by subtracting the known ABDK/BDS ansatz from the Wilson loop. First, we consider a particular two-dimensional eight-point kinematics studied at strong coupling by Alday and Maldacena. We find numerical evidence that R is the same at weak and at strong coupling, up to an overall, coupling-dependent constant. This suggests a universality of the remainder function at strong and weak coupling for generic null polygonal Wilson loops, and therefore for arbitrary MHV amplitudes in N=4 super Yang-Mills. We analyse the consequences of this statement. We further consider regular n-gons, and find that the remainder function is linear in n at large n through numerical computations performed up to n=30. This reproduces a general feature of the corresponding strong-coupling result.

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arXiv2010

Regular Wilson loops and MHV amplitudes at weak and strong coupling

Traditionally, the duality between Wilson loops and amplitudes beyond one loop in N=4 SYM is characterised by the remainder function. Because of the perturbative origins of the BDS expression, the remainder function is more natural at weak than at strong coupling. We advocate instead a more direct approach, based on considering ratios of Wilson loops. This allows us to define a manifestly finite, regularisation independent, conformally invariant quantity. It does not make a direct reference to the BDS expression and the definition is regularisation independent. It is a natural object at weak and at strong coupling, and in the latter case is directly related to the free energy of an auxiliary integrable system. We then compute these ratios for continuous families of regular polygons for 6,8 and 10 points at one and two-loops. These results are compared to expressions derived recently at strong coupling.

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arXiv2010

Two-Loop Polygon Wilson Loops in N=4 SYM

We compute for the first time the two-loop corrections to arbitrary n-gon lightlike Wilson loops in N=4 supersymmetric Yang-Mills theory, using efficient numerical methods. The calculation is motivated by the remarkable agreement between the finite part of planar six-point MHV amplitudes and hexagon Wilson loops which has been observed at two loops. At n=6 we confirm that the ABDK/BDS ansatz must be corrected by adding a remainder function, which depends only on conformally invariant ratios of kinematic variables. We numerically compute remainder functions for n=7,8 and verify dual conformal invariance. Furthermore, we study simple and multiple collinear limits of the Wilson loop remainder functions and demonstrate that they have precisely the form required by the collinear factorisation of the corresponding two-loop n-point amplitudes. The number of distinct diagram topologies contributing to the n-gon Wilson loops does not increase with n, and there is a fixed number of "master integrals", which we have computed. Thus we have essentially computed general polygon Wilson loops, and if the correspondence with amplitudes continues to hold, all planar n-point two-loop MHV amplitudes in the N=4 theory.

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arXiv2009

Phenomenology of Pure General Gauge Mediation

We investigate the phenomenology of general gauge mediation in the MSSM. We apply the strict definition of gauge mediated SUSY-breaking where B_mu is generated only through gauge interactions, and as a result is very close to zero at the messenger scale. In this setup tan beta is a prediction rather than an input. The input parameters are independent scales for the gaugino masses, the scalar masses and the messenger mass in accord with general gauge mediation. We investigate the spectra, the constraints on the parameter space from direct searches and indirect observables, as well as fine-tuning. The favoured region of parameter space includes and interpolates between non-split and mildly split SUSY, characteristic of ordinary gauge mediation and direct gauge mediation models, respectively.

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arXiv2009

Dual unified SU(5)

Despite the compelling simplicity of minimal supersymmetric unification, the proton does not decay as predicted. A possible explanation is that real unification takes place in a theory which is an electric dual of the MSSM GUT with messengers, which has Landau poles below the GUT scale. As was recently pointed out, unification predictions would be transmitted across such a duality, but proton decay would be negligible. In this paper we present electric Seiberg-duals for the minimal supersymmetric SU(5) GUT (plus messengers) that realise this idea, one particularly nice example being an asymptotically free SU(11)xSp(1)^3 model. We also discuss how gauge-mediated metastable supersymmetry breaking can be incorporated into an overall unified picture.

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arXiv2009

Gaugino versus Sfermion Masses in Gauge Mediation

A well-known signature of supersymmetry breaking scenarios with ordinary gauge mediation is a universal formula governing gaugino and sfermion masses such that their ratio is of order one. On the other hand, recently studied models with direct gauge mediation predict anomalously small ratios of gaugino to scalar masses. It was argued that the smallness of gaugino masses is a consequence of being in the lowest energy state of the SUSY-breaking low energy effective theory. To increase gaugino masses one either has to move to higher metastable vacuum or alternatively remain in the original SUSY-breaking vacuum but extend the theory by introducing a lower-lying vacuum elsewhere. We follow the latter strategy and show that the ratio of gaugino to sfermion masses can be continuously varied between zero and of order one by bringing in a lower vacuum from infinity. We argue that the stability of the vacuum is directly linked to the ratio between the gaugino masses and the underlying SUSY-breaking scale, i.e. the gravitino mass.

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arXiv2009

Magnetic Mixing -- Electric Minicharges from Magnetic Monopoles

Many extensions of the Standard Model require the existence of a "hidden" sector. We consider settings where the hidden sector in the infrared contains a U(1) gauge factor with magnetic monopoles, for instance 't Hooft-Polyakov monopoles of an underlying non-abelian gauge group. In the presence of CP violation these monopoles acquire an electric charge in the hidden sector due to the Witten effect. We show that quite generally they also acquire (small) electric charges under the visible electromagnetic gauge group. This is a result of "magnetic mixing" which, as we show, often arises as a natural partner of kinetic mixing. Both kinetic and magnetic mixing are naturally induced radiatively even if the low-energy U(1)s arise from a single non-abelian gauge group. We argue that the hidden sector monopoles can be light and their electric minicharges could thus be testable in current and near future low-energy experiments.

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arXiv2009

Patterns of Gauge Mediation in Metastable SUSY Breaking

Supersymmetry breaking in a metastable vacuum allows one to build simple and concrete models of gauge mediation. Generation of gaugino masses requires that R-symmetry be broken in this vacuum. In general, there are two possible ways to break R-symmetry, explicitly or spontaneously. We find that the MSSM phenomenology depends crucially on how this breaking occurs in the Hidden Sector. Explicit R-symmetry breaking models can lead to fairly standard gauge mediation, but we argue that in the context of ISS-type models this only makes sense if B=0 at the mediation scale, which leads to high tan(beta). If on the other hand, R-symmetry is broken spontaneously, then R-symmetry violating soft terms tend to be suppressed with respect to R-symmetry preserving ones, and one is led to a scenario with large scalar masses. These models interpolate between standard gauge mediation and split SUSY models. We provide benchmark points for the two scenarios. They demonstrate that the specific dynamics of the Hidden Sector -- the underlying nature of supersymmetry and R-symmetry breaking -- affects considerably the mass spectrum of the MSSM, and vice versa.

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arXiv2009

On the Diversity of Gauge Mediation: Footprints of Dynamical SUSY Breaking

Recent progress in realising dynamical supersymmetry breaking allows the construction of simple and calculable models of gauge mediation. We discuss the phenomenology of the particularly minimal case in which the mediation is direct, and show that there are generic new and striking predictions. These include new particles with masses comparable to those of the Standard Model superpartners, associated with the pseudo-Goldstone modes of the dynamical SUSY breaking sector. Consequently there is an unavoidable departure from the MSSM. In addition the gaugino masses are typically significantly lighter than the sfermions, and their mass ratios can be different from the pattern dictated by the gauge couplings in standard (i.e. explicit) gauge mediation. We investigate these features in two distinct realisations of the dynamical SUSY breaking sector.

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arXiv2008

Direct Mediation, Duality and Unification

It is well-known that in scenarios with direct gauge mediation of supersymmetry breaking the messenger fields significantly affect the running of Standard Model couplings and introduce Landau poles which are difficult to avoid. This appears to remove any possibility of a meaningful unification prediction and is often viewed as a strong argument against direct mediation. We propose two ways that Seiberg duality can circumvent this problem. In the first, which we call "deflected-unification", the SUSY-breaking hidden sector is a magnetic theory which undergoes a duality to an electric phase, with fewer elementary degrees of freedom coupled to the MSSM. This changes the beta-functions of the MSSM gauge couplings so as to push their Landau poles above the unification scale. We show that this scenario is realised for recently suggested models of gauge mediation based on a metastable SCQD-type hidden sector directly coupled to MSSM. The second possibility, which we call "dual-unification", begins with the observation that, if the mediating fields fall into complete SU(5) multiplets, then the MSSM+messengers exhibits a fake unification at unphysical values of the gauge couplings. We show that, in known examples of electric/magnetic duals, such a fake unification in the magnetic theory reflects a real unification in the electric theory. We therefore propose that the Standard Model could itself be a magnetic dual of some unknown electric theory in which the true unification takes place. This scenario maintains the unification prediction (and unification scale) even in the presence of Landau poles in the magnetic theory below the GUT scale. We further note that this dual realization of grand unification can explain why Nature appears to unify, but the proton does not decay.

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arXiv2008

Will the LHC Look into the Fate of the Universe?

The LHC will probe the nature of the vacuum that determines the properties of particles and the forces between them. Of particular importance is the fact that our current theories allow the Universe to be trapped in a metastable vacuum, which may decay in the distant future, changing the nature of matter. This could be the case in the Standard Model if the LHC finds the Higgs boson to be light. Supersymmetry is one favoured extension of the Standard Model which one might invoke to try to avoid such instability. However, many supersymmetric models are also condemned to vacuum decay for different reasons. The LHC will be able to distinguish between different supersymmetric models, thereby testing the stability of the vacuum, and foretelling the fate of the Universe.

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arXiv2008

MHV amplitudes in N=2 SQCD and in N=4 SYM at one loop

Using four-dimensional unitarity and MHV-rules we calculate the one-loop MHV amplitudes with all external particles in the adjoint representation for N=2 supersymmetric QCD with N_f fundamental flavours. We start by considering such amplitudes in the superconformal N=4 gauge theory where the N=4 supersymmetric Ward identities (SWI) guarantee that all MHV amplitudes for all types of external particles are given by the corresponding tree-level result times a universal helicity- and particle-type-independent contribution. In N=2 SQCD the MHV amplitudes differ from those for N=4 for general values of N_f and N_c. However, for N_f=2N_c where the N=2 SQCD is conformal, the N=2 MHV amplitudes (with all external particles in the adjoint representation) are identical to the N=4results. This factorisation at one-loop motivates us to pose a question if there may be a BDS-like factorisation for these amplitudes which also holds at higher orders of perturbation theory in superconformal N=2 theory.

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arXiv2008

Illuminating the Hidden Sector of String Theory by Shining Light through a Magnetic Field

Many models of physics beyond the Standard Model predict minicharged particles to which current and near future low-energy experiments are highly sensitive. Such minicharges arise generically from kinetic-mixing in theories containing at least two U(1) gauge factors. Here, we point out that the required multiple U(1) factors, the size of kinetic-mixing, and suitable matter representations to allow for a detection in the near future occur naturally in the context of string theory embeddings of the Standard Model. A detection of minicharged particles in a low energy experiment would likely be a signal of an underlying string theory and may provide a means of testing it.

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arXiv2008

Scattering amplitudes in strongly coupled N=4 SYM from semiclassical strings in AdS

Very recently in arXiv:0705.0303 Alday and Maldacena gave a string theory prescription for computing (all) planar amplitudes in N=4 supersymmetric gauge theory at strong coupling using the AdS/CFT correspondence. These amplitudes are determined by a classical string solution and contain a universal exponential factor involving the action of the classical string. On the gauge theory side, expressions for perturbative amplitudes at strong coupling were previously proposed only for specific helicities of external particles -- the maximally helicity violating or MHV amplitudes. These follow from the exponential ansatz of Bern, Dixon and Smirnov for MHV amplitudes in N=4 SYM. In this paper we examine the amplitudes dependence on helicities and particle-types of external states. We consider the prefactor of string amplitudes and give arguments suggesting that the prefactor at strong coupling should be the same as the Yang-Mills tree-level amplitude for the same process. This implies that scattering amplitudes in N=4 SYM simplify dramatically in the strong coupling limit. It follows from our proposal that in this limit all (MHV and non-MHV) n-point amplitudes are given by the (known) tree-level Yang-Mills result times the helicity-independent (and particle-type-independent) universal exponential.

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