arXiv subjects

Christoffer Petersson

Publications and source records attributed to Christoffer Petersson.

48 records · Page 3Linked to original sources

arXiv2012

Low Scale Supersymmetry Breaking and its LHC Signatures

We study the most general extension of the MSSM Lagrangian that includes scenarios in which supersymmetry is spontaneously broken at a low scale f. The spurion that parametrizes supersymmetry breaking in the MSSM is promoted to a dynamical superfield involving the goldstino, with (and without) its scalar superpartner, the sgoldstino. The low energy effective Lagrangian is written as an expansion in terms of m_{SUSY}/sqrt{f}, where m_{SUSY} is the induced supersymmetry breaking scale, and contains, in addition to the usual MSSM Lagrangian with the soft terms, couplings involving the component fields of the goldstino superfield and the MSSM fields. This Lagrangian can provide significant corrections to the usual couplings in the Standard Model and the MSSM. We study how these new corrections affect the Higgs couplings to gauge bosons and fermions, and how LHC bounds can be used in order to constrain f. We also discuss that, from the effective field theory point of view, the couplings of the goldstino interactions are not determined by any symmetry, and their usual simple relation to the soft terms is corrected by higher-dimensional operators.

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arXiv2012

Liberating Higgs couplings in supersymmetry

In the MSSM, the Higgs couplings to down-type quarks and leptons, normalized with respect to their corresponding Standard Model values, coincide at tree-level and this degeneracy is only slightly broken at the quantum level. Motivated by the latest results of the Higgs searches at the LHC and Tevatron, we explore the possibility of disentangling these couplings from each other by considering a scenario in which supersymmetry is broken spontaneously at a low scale. In such a scenario, all the Higgs couplings, except the ones to the Z and W bosons, receive tree level corrections that depend on the MSSM soft parameters. In particular, the corrections to the Yukawa couplings depend on the A-term soft parameter for the corresponding fermion, allowing for the freedom to break their usual relations, even in the MSSM decoupling limit. We highlight the main features of this scenario in terms of a benchmark point for which the normalized Higgs coupling to the tau leptons is depleted, the coupling to photons is enhanced, while all the other Higgs couplings, including the one to the bottom quarks, are close to their corresponding SM values. We also discuss the experimental bounds arising mainly from di-tau searches and comment on the discovery/exclusion prospects at the LHC.

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arXiv2012

Higgs decay with monophoton + MET signature from low scale supersymmetry breaking

We study the decay of a standard model-like Higgs boson into a gravitino and a neutralino, which subsequently decays promptly into another gravitino and a photon. Such a decay can be important in scenarios where the supersymmetry breaking scale is of the order of a few TeV, and in the region of low transverse momenta of the photon, it may provide the dominant contribution to the final state with a photon and two gravitinos. We estimate the relevant standard model backgrounds and the prospects for discovering this Higgs decay through a photon and missing transverse energy signal at the LHC in terms of a simplified model. We also give an explicit model with manifest, but spontaneously broken, supersymmetry in which the usual MSSM soft terms are promoted to supersymmetric operators involving a dynamical goldstino supermultiplet. This model can give rise to a SM-like CP-even neutral Higgs particle with a mass of 125 GeV, without requiring substantial radiative corrections, and with couplings sufficiently large for a signal discovery through the above mentioned Higgs decay channel with the upcoming data from the LHC.

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arXiv2012

Photophilic Higgs from sgoldstino mixing

The spontaneous breaking of linearly realized N=1 supersymmetry implies the existence of a pseudo-Goldstone fermion, the goldstino, and of its complex scalar superpartner, the sgoldstino. The latter has generically sizable tree-level couplings to Standard Model gauge bosons while its couplings to SM fermions are suppressed. We consider a light sgoldstino, with a mass around 1 TeV, that mixes with a SM-like Higgs scalar at around 125 GeV. We show that such a mixing can enhance the Higgs to di-photon signal rate while evading all the relevant experimental bounds and without significantly affecting the other decay channels.

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arXiv2012

The MSSM Higgs Sector with a Dynamical Goldstino Supermultiplet

We consider a supersymmetric realization of the MSSM Higgs sector, where the soft terms are promoted to supersymmetric operators and a minimal weakly coupled hidden sector is included. The model exhibits long-lived meta-stable vacua in which supersymmetry and electroweak symmetry are spontaneously broken. The spectrum contains, in addition to the usual MSSM particles and the goldstino fermion, a CP-even and a CP-odd scalar in the neutral Higgs sector corresponding to the complex sgoldstino scalar. By treating all the components of the goldstino supermultiplet dynamically and taking into account their interactions with the Higgs fields, additional couplings beyond those of the MSSM are induced. When the supersymmetry breaking scale is low, these couplings can raise the masses of all the Higgs particles above the LEP bound, already at tree level and for any value of tan(beta). The model includes a scenario where, for any choice of the supersymmetry breaking scale, the set of parameters is reduced to the standard set (mu, Bmu, tan(beta)) of the MSSM Higgs sector but where novel decays of doublet-like states into sgoldstino-like states are kinematically allowed.

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arXiv2010

D-instanton and polyinstanton effects from type I' D0-brane loops

We study non-perturbative D(-1)-instanton corrections to quartic gauge and curvature couplings in 8d type IIB orientifolds, in terms of a one-loop computation of BPS D0-branes in T-dual type I' models. The complete perturbative and non-perturbative results are determined by the BPS multiplicities of perturbative open strings and D0-brane bound states in the 9d type I' theory. Its modular properties admit a geometric interpretation by lifting to Horava-Witten theory. We use the type I' viewpoint to motivate a proper interpretation of 8d and 4d polyinstanton effects, consistent with heterotic - type II orientifold duality.

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arXiv2009

Non-Perturbative Effects on a Fractional D3-Brane

In this note we study the N=1 abelian gauge theory on the world volume of a single fractional D3-brane. In the limit where gravitational interactions are not completely decoupled we find that a superpotential and a fermionic bilinear condensate are generated by a D-brane instanton effect. A related situation arises for an isolated cycle invariant under an orientifold projection, even in the absence of any gauge theory brane. Moreover, in presence of supersymmetry breaking background fluxes, such instanton configurations induce new couplings in the 4-dimensional effective action, including non-perturbative contributions to the cosmological constant and non-supersymmetric mass terms.

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arXiv2008

On relating multiple M2 and D2-branes

Due to the difficulties of finding superconformal Lagrangian theories for multiple M2-branes, we will in this paper instead focus on the field equations. By relaxing the requirement of a Lagrangian formulation we can explore the possibility of having structure constants $f^{ABC}{}_D$ satisfying the fundamental identity but which are not totally antisymmetric. We exemplify this discussion by making use of an explicit choice of a non-antisymmetric $f^{ABC}{}_D$ constructed from the Lie algebra structure constants $f^{ab}{}_c$ of an arbitrary gauge group. Although this choice of $f^{ABC}{}_D$ does not admit an obvious Lagrangian description, it does reproduce the correct SYM theory for a stack of $N$ D2-branes to leading order in $g_{YM}^{-1}$ upon reduction and, moreover, it sheds new light on the centre of mass coordinates for multiple M2-branes.

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arXiv2008

Instantons and Toric Quiver Gauge Theories

We show how to construct the general action coupling (multi)instantons to gauge theories arising from branes probing arbitrary toric singularities. We give a general set of rules for how to construct such an action given the knowledge of the superpotential for the gauge theory. The main idea is to obtain the action by higgsing a theory whose instanton dynamics is known, namely an orbifold of N=4 super Yang-Mills. We find that the couplings of the fermionic zero-modes with the holomorphic fields are dictated by the structure of the superpotential describing the toric singularity. We present explicit examples such as the Suspended Pinch Point, the Conifold and the first three del Pezzo's. We perform various checks on these results by further higgsing to smaller orbifolds and present some applications, including both gauge theory and stringy instantons.

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arXiv2008

Superpotentials From Stringy Instantons Without Orientifolds

In this paper we show that it is possible to derive non-perturbative superpotential terms from a stringy instanton without introducing orientifold planes. The instanton is realized by a Euclidean D brane wrapping a non-trivial cycle upon which we also wrap a single space-filling D brane. The standard problem of unwanted neutral fermionic zero modes is evaded by the appearance of couplings to charged bosonic zero modes in the instanton moduli action. Since the Euclidean D brane wraps a cycle which is not associated to any low energy gauge dynamics, it can not be interpreted as an ordinary gauge instanton, but rather as a stringy one. By considering such a brane configuration at an orbifold singularity, we can explicitly evaluate the instanton moduli space integral and find a holomorphic superpotential term with the structure of a baryonic mass term.

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arXiv2007

Stringy Instantons at Orbifold Singularities

We study the effects produced by D-brane instantons on the holomorphic quantities of a D-brane gauge theory at an orbifold singularity. These effects are not limited to reproducing the well known contributions of the gauge theory instantons but also generate extra terms in the superpotential or the prepotential. On these brane instantons there are some neutral fermionic zero-modes in addition to the ones expected from broken supertranslations. They are crucial in correctly reproducing effects which are dual to gauge theory instantons, but they may make some other interesting contributions vanish. We analyze how orientifold projections can remove these zero-modes and thus allow for new superpotential terms. These terms contribute to the dynamics of the effective gauge theory, for instance in the stabilization of runaway directions.

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arXiv2006

Massless fermionic bound states and the gauge/gravity correspondence

We study the equations of motion of fermions in type IIB supergravity in the context of the gauge/gravity correspondence. The main motivation is the search for normalizable fermionic zero modes in such backgrounds, to be interpreted as composite massless fermions in the dual theory. We specialize to backgrounds characterized by a constant dilaton and a self-dual three-form. In the specific case of the Klebanov--Strassler solution we construct explicitly the fermionic superpartner of the Goldstone mode associated with the broken baryonic symmetry. The fermionic equations could also be used to search for goldstinos in theories that break supersymmetry dynamically.

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