Publications by John March-Russell

Towards a Swampland Global Symmetry Conjecture using Weak Gravity

arXiv (2020)

T Daus, A Hebecker, S Leonhardt, J March-Russell

It is widely believed and in part established that exact global symmetries are inconsistent with quantum gravity. One then expects that approximate global symmetries can be quantitatively constrained by quantum gravity or swampland arguments. We provide such a bound for an important class of global symmetries: Those arising from a gauged $U(1)$ with the vector made massive via a Nambu-Goldstone mode. The latter is an axion which necessarily couples to instantons, and their action can be constrained, using both the electric and magnetic version of the axionic weak gravity conjecture, in terms of the cutoff of the theory. As a result, instanton-induced symmetry breaking operators with a suppression factor not smaller than $\exp(-M_{\rm P}^2/\Lambda^2)$ are present, where $\Lambda$ is a cutoff of the 4d effective theory. We provide a general argument and clarify the meaning of $\Lambda$. Simple 4d and 5d models are presented to illustrate this, and we recall that this is the standard way in which things work out in string compactifications with brane instantons. We discuss the relation of our constraint to bounds that can be derived from wormholes or gravitational instantons and to those motivated by black-hole effects at finite temperature. Finally, we discuss potential loopholes to our arguments.

Hawking radiation of extended objects


G Johnson, J March-Russell

The string soundscape at gravitational wave detectors

PHYSICS LETTERS B 779 (2018) 348-352

I Garcia Garcia, S Krippendorf, J March-Russell

Black hole genesis of dark matter


O Lennon, J March-Russell, R Petrossian-Byrne, H Tillim

Higgs assisted Q-balls from pseudo-Nambu-Goldstone bosons


F Bishara, G Johnson, O Lennon, J March-Russell

Baryogenesis via particle-antiparticle oscillations

Physical Review D American Physical Society 93 (2016)

S Ipek, J March-Russell

CP violation, which is crucial for producing the baryon asymmetry of the Universe, is enhanced in particle-antiparticle oscillations. We study particle-antiparticle oscillations [of a particle with mass O(100 GeV)] with CP violation in the early Universe in the presence of interactions with O(ab-fb) cross sections. We show that if baryon-number-violating interactions exist, a baryon asymmetry can be produced via out-of-equilibrium decays of oscillating particles. As a concrete example we study a U(1)R-symmetric, R-parity-violating supersymmetry model with pseudo-Dirac gauginos, which undergo particle-antiparticle oscillations. Taking bino to be the lightest U(1)R-symmetric particle, and assuming it decays via baryon-number-violating interactions, we show that bino-antibino oscillations can produce the baryon asymmetry of the Universe.

Natural Scherk-Schwarz theories of the weak scale


IG Garcia, K Howe, J March-Russell

Twin Higgs WIMP dark matter

PHYSICAL REVIEW D 92 (2015) ARTN 055034

IG Garcia, R Lasenby, J March-Russell

Twin Higgs Asymmetric Dark Matter.

Physical review letters 115 (2015) 121801-

I García García, R Lasenby, J March-Russell

We study asymmetric dark matter (ADM) in the context of the minimal (fraternal) twin Higgs solution to the little hierarchy problem, with a twin sector with gauged SU(3)^{'}×SU(2)^{'}, a twin Higgs doublet, and only third-generation twin fermions. Naturalness requires the QCD^{'} scale Λ_{QCD}^{'}≃0.5-20  GeV, and that t^{'} is heavy. We focus on the light b^{'} quark regime, m_{b^{'}}≲Λ_{QCD}^{'}, where QCD^{'} is characterized by a single scale Λ_{QCD}^{'} with no light pions. A twin baryon number asymmetry leads to a successful dark matter (DM) candidate: the spin-3/2 twin baryon, Δ^{'}∼b^{'}b^{'}b^{'}, with a dynamically determined mass (∼5Λ_{QCD}^{'}) in the preferred range for the DM-to-baryon ratio Ω_{DM}/Ω_{baryon}≃5. Gauging the U(1)^{'} group leads to twin atoms (Δ^{'}-τ^{'}[over ¯] bound states) that are successful ADM candidates in significant regions of parameter space, sometimes with observable changes to DM halo properties. Direct detection signatures satisfy current bounds, at times modified by dark form factors.

Signatures of large composite Dark Matter states


E Hardy, R Lasenby, J March-Russell, SM West

Auto-concealment of supersymmetry in extra dimensions


S Dimopoulos, K Howe, J March-Russell, J Scoville

Big Bang synthesis of nuclear dark matter


E Hardy, R Lasenby, J March-Russell, SM West

Rare flavor processes in Maximally Natural Supersymmetry

Journal of High Energy Physics 2015 (2015)

IG García, J March-Russell

© 2015, The Author(s). Abstract: We study CP-conserving rare flavor violating processes in the recently proposed theory of Maximally Natural Supersymmetry (MNSUSY). MNSUSY is an unusual supersymmetric (SUSY) extension of the Standard Model (SM) which, remarkably, is untuned at present LHC limits. It employs Scherk-Schwarz breaking of SUSY by boundary conditions upon compactifying an underlying 5-dimensional (5D) theory down to 4D, and is not well-described by softly-broken N=1$$ \mathcal{N}=1 $$ SUSY, with much different phenomenology than the Minimal Supersymmetric Standard Model (MSSM) and its variants. The usual CP-conserving SUSY-flavor problem is automatically solved in MNSUSY due to a residual almost exact U(1)R symmetry, naturally heavy and highly degenerate 1st- and 2nd-generation sfermions, and heavy gauginos and Higgsinos. Depending on the exact implementation of MNSUSY there exist important new sources of flavor violation involving gauge boson Kaluza-Klein (KK) excitations. The spatial localization properties of the matter multiplets, in particular the brane localization of the 3rd generation states, imply KK-parity is broken and tree-level contributions to flavor changing neutral currents are present in general. Nevertheless, we show that simple variants of the basic MNSUSY model are safe from present flavor constraints arising from kaon and B-meson oscillations, the rare decays Bs,d → μ+μ−, μ → ēee and μ-e conversion in nuclei. We also briefly discuss some special features of the radiative decays μ → eγ and B¯→Xsγ$$ \overline{B}\to {X}_s\gamma $$. Future experiments, especially those concerned with lepton flavor violation, should see deviations from SM predictions unless one of the MNSUSY variants with enhanced flavor symmetries is realized.

Maximally natural supersymmetry.

Physical review letters 113 (2014) 111802-

S Dimopoulos, K Howe, J March-Russell

We consider 4D weak scale theories arising from 5D supersymmetric (SUSY) theories with maximal Scherk-Schwarz breaking at a Kaluza-Klein scale of several TeV. Many of the problems of conventional SUSY are avoided. Apart from 3rd family sfermions the SUSY spectrum is heavy, with only ∼50% tuning at a gluino mass of ∼2  TeV and a stop mass of ∼650  GeV. A single Higgs doublet acquires a vacuum expectation value, so the physical Higgs boson is automatically standard-model-like. A new U(1)^{'} interaction raises m_{h} to 126 GeV. For minimal tuning the associated Z^{'}, as well as the 3rd family sfermions, must be accessible to LHC13. A gravitational wave signal consistent with hints from BICEP2 is possible if inflation occurs when the extra dimensions are small.

Boosted objects: A probe of beyond the standard model physics

European Physical Journal C Springer-Verlag 71 (2011)

A Abdesselam, A Belyaev, A Belyaev, E Bergeaas Kuutmann, U Bitenc, G Brooijmans, J Butterworth, P Bruckman de Renstrom, D Buarque Franzosi, R Buckingham, B Chapleau, M Dasgupta, A Davison, J Dolen, S Ellis, F Fassi, J Ferrando, MT Frandsen, J Frost, T Gadfort, N Glover, A Haas, E Halkiadakis, K Hamilton, C Hays

We present the report of the hadronic working group of the BOOST2010 workshop held at the University of Oxford in June 2010. The first part contains a review of the potential of hadronic decays of highly boosted particles as an aid for discovery at the LHC and a discussion of the status of tools developed to meet the challenge of reconstructing and isolating these topologies. In the second part, we present new results comparing the performance of jet grooming techniques and top tagging algorithms on a common set of benchmark channels. We also study the sensitivity of jet substructure observables to the uncertainties in Monte Carlo predictions.

A supersymmetric one Higgs doublet model

Journal of High Energy Physics 2011 (2011)

R Davies, J March-Russell, M McCullough

We present a supersymmetric extension of the Standard Model in which only one electroweak doublet acquires a vacuum expectation value and gives mass to Standard Model fermions. As well as the novel accommodation of a Standard Model Higgs within a supersymmetric framework, this leads to a very predictive model, with some advantages over the MSSM. In particular, problems with proton decay, flavour changing neutral currents and large CP violation are ameliorated, primarily due to the presence of an anomalyfree R-symmetry. Since supersymmetry must be broken at a low scale, gravity-mediated effects which break the R-symmetry are naturally small. The R-symmetry requires the presence of adjoint chiral superfields, to give Dirac masses to the gauginos; these adjoints are the only non-MSSM fields in the visible sector. The LSP is a very light neutralino, which is mostly bino. Such a light neutralino is not in conflict with experiment, and is a striking prediction of the minimal model. Additional scenarios to raise the mass of this neutralino to the weak scale are also outlined. Prospects for discovery at the LHC are briefly discussed, along with viable scenarios for achieving gauge-coupling unification. © SISSA 2011.

On the DAMA and CoGeNT modulations

PHYSICAL REVIEW D 84 (2011) ARTN 041301

MT Frandsen, F Kahlhoefer, J March-Russell, C McCabe, M McCullough, K Schmidt-Hoberg

On the DAMA and CoGeNT modulations

Physical Review D - Particles, Fields, Gravitation and Cosmology 84 (2011)

MT Frandsen, F Kahlhoefer, J March-Russell, C McCabe, M McCullough, K Schmidt-Hoberg

DAMA observes an annual modulation in their event rate, as might be expected from dark matter scatterings, while CoGeNT has reported evidence for a similar modulation. The simplest interpretation of these findings in terms of dark matter-nucleus scatterings is excluded by other direct detection experiments. We consider the robustness of these exclusions with respect to assumptions regarding the scattering and find that isospin-violating inelastic dark matter helps alleviate this tension and allows marginal compatibility between experiments. Isospin violation can significantly weaken the XENON constraints, while inelasticity enhances the annual modulation fraction of the signal, bringing the CoGeNT and CDMS results into better agreement. © 2011 American Physical Society.

A Supersymmetric One Higgs Doublet Model

JHEP 1104 (2011) 108-108

R Davies, J March-Russell, M McCullough

The goldstini variations


N Craig, J March-Russell, M McCullough

We study the 'goldstini' scenario of Cheung, Nomura, and Thaler, in which multiple independent supersymmetry (SUSY) breaking sectors lead to multiple would-be goldstinos, changing collider and cosmological phenomenology. In supergravity, potentially large corrections to the previous prediction of twice the gravitino mass for goldstini masses can arise when their scalar partners are stabilized far from the origin. Considerations arising from the complexity of realistic string compactifications indicate that many of the independent SUSY-breaking sectors should be conformally sequestered or situated in warped Randall-Sundrum-like throats, further changing the predicted goldstini masses. If the sequestered hidden sector is a metastable SUSY-breaking sector of the Intriligator-Seiberg-Shih (ISS) type then multiple goldstini can originate from within a single sector, along with many supplementary 'modulini', all with masses of order twice the gravitino mass. These fields can couple to the Supersymmetric Standard Model (SSM) via the 'Goldstino Portal'. Collider signatures involving SSM sparticle decays can provide strong evidence for warped-or-conformally-sequestered sectors, and of the ISS mechanism of SUSY breaking. Along with axions and photini, the Goldstino Portal gives another potential window to the hidden sectors of string theory.