# John Ellis - King's College London & CERN

## Contact Details

NameJohn Ellis |
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AffiliationKing's College London & CERN |
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Location |
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## Pubs By Year |
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## Pub CategoriesHigh Energy Physics - Phenomenology (44) High Energy Physics - Experiment (23) High Energy Physics - Theory (19) Cosmology and Nongalactic Astrophysics (14) General Relativity and Quantum Cosmology (11) High Energy Astrophysical Phenomena (5) Physics - Materials Science (2) Mathematics - Mathematical Physics (1) Computer Science - Data Structures and Algorithms (1) Mathematical Physics (1) Nuclear Experiment (1) Physics - Optics (1) Solar and Stellar Astrophysics (1) Earth and Planetary Astrophysics (1) |

## Publications Authored By John Ellis

We explore the constraints imposed by the cancellation of triangle anomalies on models in which the flavour anomalies reported by LHCb and other experiments are due to an extra U(1)' gauge boson Z'. We assume universal and rational U(1)' charges for the first two generations of left-handed quarks and of right-handed up-type quarks but allow different charges for their third-generation counterparts. If the right-handed charges vanish, cancellation of all the triangle anomalies requires all the quark U(1)' charges to vanish, if there are no fermions beyond those in the Standard Model (SM), or if there is only one SM-singlet dark matter (DM) fermion. Read More

We embed a flipped ${\rm SU}(5) \times {\rm U}(1)$ GUT model in a no-scale supergravity framework, and discuss its predictions for cosmic microwave background observables, which are similar to those of the Starobinsky model of inflation. Measurements of the tilt in the spectrum of scalar perturbations in the cosmic microwave background, $n_s$, constrain significantly the model parameters. We also discuss the model's predictions for neutrino masses, and pay particular attention to the behaviours of scalar fields during and after inflation, reheating and the GUT phase transition. Read More

We have studied the topological insulator Bi$_2$Te$_3$(111) by means of helium atom scattering. The average electron-phonon coupling $\lambda$ of Bi$_2$Te$_3$(111) is determined by adapting a recently developed quantum-theoretical derivation of the helium scattering probabilities to the case of degenerate semiconductors. Based on the Debye-Waller attenuation of the elastic diffraction peaks of Bi$_2$Te$_3$(111), measured at surface temperatures between $110~\mbox{K}$ and $355~\mbox{K}$, we find $\lambda$ to be in the range of $0. Read More

We explore the anomaly-cancellation constraints on simplified dark matter (DM) models with an extra U(1)$^\prime$ gauge boson $Z'$. We show that, if the Standard Model (SM) fermions are supplemented by a single DM fermion $\chi$ that is a singlet of the SM gauge group, and the SM quarks have non-zero U(1)$^\prime$ charges, the SM leptons must also have non-zero U(1)$^\prime$ charges, in which case LHC searches impose strong constraints on the $Z'$ mass. Moreover, the DM fermion $\chi$ must have a vector-like U(1)$^\prime$ coupling. Read More

The answer to the question in the title is: in search of new physics beyond the Standard Model, for which there are many motivations, including the likely instability of the electroweak vacuum, dark matter, the origin of matter, the masses of neutrinos, the naturalness of the hierarchy of mass scales, cosmological inflation and the search for quantum gravity. So far, however, there are no clear indications about the theoretical solutions to these problems, nor the experimental strategies to resolve them. It makes sense now to prepare various projects for possible future accelerators, so as to be ready for decisions when the physics outlook becomes clearer. Read More

The recent measurement by ATLAS of light-by-light scattering in LHC Pb-Pb collisions is the first direct evidence for this basic process. We find that it requires the mass scale of a nonlinear Born-Infeld extension of QED to be $\gtrsim 100$~GeV, a much stronger constraint than those derived previously. In the case of a Born-Infeld extension of the Standard Model in which the U(1)$_{\rm Y}$ hypercharge gauge symmetry is realized nonlinearly, the limit on the corresponding mass scale is $\gtrsim 90$~GeV, which in turn imposes a lower limit of $\gtrsim 11$~TeV on the magnetic monopole mass in such a U(1)$_{\rm Y}$ Born-Infeld theory. Read More

These lecture notes review the theoretical background to the Higgs boson, provide an introduction to its phenomenology, and describe the experimental tests that lead us to think that "beyond any reasonable doubt, it is a Higgs boson". Motivations for expecting new physics beyond the Standard Model are recalled, and the Standard Model effective field theory is advocated as a tool to help search for it. The phenomenology of $N = 1$ and $N = 2$ supersymmetric Higgs bosons is reviewed, and the prospects for possible future Higgs factories are previewed. Read More

We reconsider the minimal SU(5) Grand Unified Theory (GUT) in the context of no-scale supergravity, assuming that the soft supersymmetry-breaking parameters satisfy universality conditions at some input scale M_in above the GUT scale M_GUT. When setting up such a no-scale super-GUT model, special attention must be paid to avoiding the Scylla of rapid proton decay and the Charybdis of an excessive density of cold dark matter, while also having an acceptable mass for the Higgs boson. We do not find consistent solutions if none of the matter and Higgs fields are assigned to twisted chiral supermultiplets, even in the presence of Giudice-Masiero terms. Read More

We estimate the possible accuracies of measurements at the proposed CLIC $e^+e^-$ collider of Higgs and $W^+W^-$ production at centre-of-mass energies up to 3TeV, incorporating also Higgsstrahlung projections at higher energies that had not been considered previously, and use them to explore the prospective CLIC sensitivities to decoupled new physics. We present the resulting constraints on the Wilson coefficients of dimension-6 operators in a model-independent approach based on the Standard Model effective field theory (SM EFT). The higher centre-of-mass energy of CLIC, compared to other projects such as the ILC and CEPC, gives it greater sensitivity to the coefficients of some of the operators we study. Read More

The photon mass, $m_\gamma$, can in principle be constrained using measurements of the dispersion measures (DMs) of fast radio bursts (FRBs), once the FRB redshifts are known. The DM of the repeating FRB 121102 is known to $< 1$\%, a host galaxy has now been identified with high confidence,and its redshift, $z$, has now been determined with high accuracy: $z = 0.19273(8)$. Read More

Helium spin echo experiments combined with ab initio-based Langevin molecular dynamics simulations are used to quantify the adsorbate-substrate coupling during the thermal diffusion of Na atoms on Cu(111). An analysis of trajectories within the local density friction approximation allows the contribution from electron-hole pair excitations to be separated from the total energy dissipation. Despite the minimal electronic friction coefficient of Na and the relatively small mass mismatch to Cu promoting efficient phononic dissipation, about $(20\pm5)\%$ of the total energy loss is attributable to electronic friction. Read More

Using a no-scale supergravity framework, we construct an SO(10) model that makes predictions for cosmic microwave background observables similar to those of the Starobinsky model of inflation, and incorporates a double-seesaw model for neutrino masses consistent with oscillation experiments and late-time cosmology. We pay particular attention to the behaviour of the scalar fields during inflation and the subsequent reheating. Read More

We revisit minimal supersymmetric SU(5) grand unification (GUT) models in which the soft supersymmetry-breaking parameters of the minimal supersymmetric Standard Model (MSSM) are universal at some input scale, $M_{in}$, above the supersymmetric gauge coupling unification scale, $M_{GUT}$. As in the constrained MSSM (CMSSM), we assume that the scalar masses and gaugino masses have common values, $m_0$ and $m_{1/2}$ respectively, at $M_{in}$, as do the trilinear soft supersymmetry-breaking parameters $A_0$. Going beyond previous studies of such a super-GUT CMSSM scenario, we explore the constraints imposed by the lower limit on the proton lifetime and the LHC measurement of the Higgs mass, $m_h$. Read More

**Authors:**Andreas Albert, Martin Bauer, Oliver Buchmueller, Jim Brooke, David G. Cerdeno, Matthew Citron, Gavin Davies, Annapaola de Cosa, Albert De Roeck, Andrea De Simone, Tristan Du Pree, John Ellis, Henning Flaecher, Malcolm Fairbairn, Alexander Grohsjean, Kristian Hahn, Ulrich Haisch, Philip C. Harris, Valentin V. Khoze, Greg Landsberg, Christopher McCabe, Bjoern Penning, Veronica Sanz, Christian Schwanenberger, Pat Scott, Nicholas Wardle

This White Paper is an input to the ongoing discussion about the extension and refinement of simplified Dark Matter (DM) models. Based on two concrete examples, we show how existing simplified DM models (SDMM) can be extended to provide a more accurate and comprehensive framework to interpret and characterise collider searches. In the first example we extend the canonical SDMM with a scalar mediator to include mixing with the Higgs boson. Read More

We explore the possibility that physics at the TeV scale possesses approximate $N = 2$ supersymmetry, which is reduced to the $N=1$ minimal supersymmetric extension of the Standard Model (MSSM) at the electroweak scale. This doubling of supersymmetry modifies the Higgs sector of the theory, with consequences for the masses, mixings and couplings of the MSSM Higgs bosons, whose phenomenological consequences we explore in this paper. The mass of the lightest neutral Higgs boson $h$ is independent of $\tan \beta$ at the tree level, and the decoupling limit is realized whatever the values of the heavy Higgs boson masses. Read More

We extend our previous study of supersymmetric Higgs inflation in the context of no-scale supergravity and grand unification, to include models based on the flipped SU(5) and the Pati-Salam group. Like the previous SU(5) GUT model, these yield a class of inflation models whose inflation predictions interpolate between those of the quadratic chaotic inflation and Starobinsky-like inflation, while avoiding tension with proton decay limits. We further analyse the reheating process in these models, and derive the number of e-folds, which is independent of the reheating temperature. Read More

We have argued previously, based on the analysis of two-dimensional stringy black holes, that information in stringy versions of four-dimensional Schwarzschild black holes (whose singular regions are represented by appropriate Wess-Zumino-Witten models) is retained by quantum $W$-symmetries when the horizon area is not preserved due to Hawking radiation. It is key that the exactly-marginal conformal world-sheet operator representing a massless stringy particle interacting with the black hole requires a contribution from $W_\infty$ generators in its vertex function. The latter correspond to delocalised, non-propagating, string excitations that guarantee the transfer of information between the string black hole and external particles. Read More

**Affiliations:**

^{1}King's Coll. London,

^{2}Minnesota U., Theor. Phys. Inst,

^{3}University of Bergen, DPT

**Category:**High Energy Physics - Phenomenology

We consider supersymmetric grand unified theories with soft supersymmetry-breaking scalar masses $m_0$ specified above the GUT scale (super-GUTs) and patterns of Yukawa couplings motivated by upper limits on flavour-changing interactions beyond the Standard Model. If the scalar masses are smaller than the gaugino masses $m_{1/2}$, as is expected in no-scale models, the dominant effects of renormalization between the input scale and the GUT scale are generally expected to be those due to the gauge couplings, which are proportional to $m_{1/2}$ and generation-independent. In this case, the input scalar masses $m_0$ may violate flavour maximally, a scenario we call MaxSFV, and there is no supersymmetric flavour problem. Read More

We consider interference effects in the production via gluon fusion in LHC collisions at 13 TeV and decays into $\gamma \gamma$ and $t {\bar t}$ final states of one or two putative new resonant states $\Phi$, assumed here to be scalar and/or pseudo scalar particles. Although our approach is general, we use for our numerical analysis the example of the putative $750$ GeV state for which a slight excess was observed in the initial LHC $13$ TeV data. We revisit previous calculations of the interferences between the heavy-fermion loop-induced $gg \to \Phi \to \gamma \gamma$ signal and the continuum $gg\to \gamma\gamma$ QCD background, which can alter the production rate as well as modify the line-shape and apparent mass. Read More

Several searches have found evidence of $^{60}$Fe deposition, presumably from a near-Earth supernova (SN), with concentrations that vary in different locations on Earth. This paper examines various influences on the path of interstellar dust carrying $^{60}$Fe from a SN through the heliosphere, with the aim of estimating the final global distribution on the ocean floor. We study the influences of magnetic fields, angle of arrival, wind and ocean cycling of SN material on the concentrations at different locations. Read More

One item on the agenda of future colliders is certain to be the Higgs boson. What is it trying to tell us? The primary objective of any future collider must surely be to identify physics beyond the Standard Model, and supersymmetry is one of the most studied options. it Is supersymmetry waiting for us and, if so, can LHC Run 2 find it? The big surprise from the initial 13-TeV LHC data has been the appearance of a possible signal for a new boson X with a mass ~750 GeV. Read More

We discuss the observability of neutrino-induced sphaleron transitions in the IceCube detector, encouraged by a recent paper by Tye and Wong (TW), which argued on the basis of a Bloch wave function in the periodic sphaleron potential that such transitions should be enhanced compared to most previous calculations. We calculate the dependence on neutrino energy of the sphaleron transition rate, comparing it to that for conventional neutrino interactions, and we discuss the observability of tau and multi-muon production in sphaleron-induced transitions. We use IceCube 4-year data to constrain the sphaleron rate, finding that it is comparable to the upper limit inferred previously from a recast of an ATLAS search for microscopic black holes at the LHC with $\sim 3$/fb of collisions at 13 TeV. Read More

The frequency-dependent time delays in fast radio bursts (FRBs) can be used to constrain the photon mass, if the FRB redshifts are known, but the similarity between the frequency dependences of dispersion due to plasma effects and a photon mass complicates the derivation of a limit on $m_\gamma$. The dispersion measure (DM) of FRB 150418 is known to $\sim 0.1$%, and there is a claim to have measured its redshift with an accuracy of $\sim 2$%, but the strength of the constraint on $m_\gamma$ is limited by uncertainties in the modelling of the host galaxy and the Milky Way, as well as possible inhomogeneities in the intergalactic medium (IGM). Read More

Cosmology and particle physics have long been dominated by theoretical paradigms: Einstein's general theory of relativity in cosmology and the Standard Model of particle physics. The time may have come for paradigm shifts. Does cosmological inflation require a modification of Einstein's gravity? Have experiments at the LHC discovered a new particle beyond the Standard Model? It is premature to answer these questions, but we theorists can dream about the possibilities. Read More

The observation of gravitational waves from the Laser Interferometer Gravitational-Wave Observatory (LIGO) event GW150914 may be used to constrain the possibility of Lorentz violation in graviton propagation, and the observation by the Fermi Gamma-Ray Burst Monitor of a transient source in apparent coincidence may be used to constrain the difference between the velocities of light and gravitational waves: $c_g - c_\gamma < 10^{-17}$. Read More

In a recent paper, Cho, Kim and Yoon (CKY) have proposed a version of the SU(2) $\times$ U(1) Standard Model with finite-energy monopole and dyon solutions. The CKY model postulates that the effective U(1) gauge coupling $\to \infty$ very rapidly as the Englert-Brout-Higgs vacuum expectation value $\to 0$, but in a way that is incompatible with LHC measurements of the Higgs boson $H \to \gamma \gamma$ decay rate. We construct generalizations of the CKY model that are compatible with the $H \to \gamma \gamma$ constraint, and calculate the corresponding values of the monopole and dyon masses. Read More

In a recent paper, Tye and Wong (TW) have argued that sphaleron-induced transitions in high-energy proton-proton collisions should be enhanced compared to previous calculations, based on a construction of a Bloch wave function in the periodic sphaleron potential and the corresponding pass band structure. Here we convolute the calculations of TW with parton distribution functions and simulations of final states to explore the signatures of sphaleron transitions at the LHC and possible future colliders. We calculate the increase of sphaleron transition rates in proton-proton collisions at centre-of-mass energies of 13/14/33/100 TeV for different sphaleron barrier heights, while recognising that the rates have large overall uncertainties. Read More

If the recent indications of a possible state $\Phi$ with mass $\sim 750$ GeV decaying into two photons reported by ATLAS and CMS in LHC collisions at 13 TeV were to become confirmed, the prospects for future collider physics at the LHC and beyond would be affected radically, as we explore in this paper. Even minimal scenarios for the $\Phi$ resonance and its $\gamma \gamma$ decays require additional particles with masses $\gtrsim \frac12 m_\Phi$. We consider here two benchmark scenarios that exemplify the range of possibilities: one in which $\Phi$ is a singlet scalar or pseudoscalar boson whose production and $\gamma \gamma$ decays are due to loops of coloured and charged fermions, and another benchmark scenario in which $\Phi$ is a superposition of (nearly) degenerate CP-even and CP-odd Higgs bosons in a (possibly supersymmetric) two-Higgs doublet model also with additional fermions to account for the $\gamma \gamma$ decay rate. Read More

We revisit gravitino production following inflation. As a first step, we review the standard calculation of gravitino production in the thermal plasma formed at the end of post-inflationary reheating when the inflaton has completely decayed. Next we consider gravitino production prior to the completion of reheating, assuming that the inflaton decay products thermalize instantaneously while they are still dilute. Read More

We consider interpretations of the recent $\sim 3 \sigma$ reports by the CMS and ATLAS collaborations of a possible $X(\sim 750~{\rm GeV})$ state decaying into $\gamma \gamma$ final states. We focus on the possibilities that this is a scalar or pseudoscalar electroweak isoscalar state produced by gluon-gluon fusion mediated by loops of heavy fermions. We consider several models for these fermions, including a single vector-like charge $2/3$ T quark, a doublet of vector-like quarks $(T, B)$, and a vector-like generation of quarks, with or without leptons that also contribute to the $X \to \gamma \gamma$ decay amplitude. Read More

We present the universal one-loop effective action for all operators of dimension up to six obtained by integrating out massive, non-degenerate multiplets. Our general expression may be applied to loops of heavy fermions or bosons, and has been checked against partial results available in the literature. The broad applicability of this approach simplifies one-loop matching from an ultraviolet model to a lower-energy effective field theory (EFT), a procedure which is now reduced to the evaluation of a combination of matrices in our universal expression, without any loop integrals to evaluate. Read More

We introduce a new prescription for quantising scalar field theories perturbatively around a true minimum of the full quantum effective action, which is to `complete normal order' the bare action of interest. When the true vacuum of the theory is located at zero field value, the key property of this prescription is the automatic cancellation, to any finite order in perturbation theory, of all tadpole and, more generally, all `cephalopod' Feynman diagrams. The latter are connected diagrams that can be disconnected into two pieces by cutting one internal vertex, with either one or both pieces free from external lines. Read More

Building upon our previous work on two-dimensional stringy black holes and its extension to spherically-symmetric four-dimensional stringy black holes, we show how the latter retain information. A key r\^ole is played by an infinite-dimensional $W_\infty$ symmetry that preserves the area of an isolated black-hole horizon and hence its entropy. The exactly-marginal conformal world-sheet operator representing a massless stringy particle interacting with the black hole necessarily includes a contribution from $W_\infty$ generators in its vertex function. Read More

Run 1 of the LHC has provided three new motivations for supersymmetry: the need to stabilize the electroweak vacuum, the mass of the Higgs boson, and the fact that its couplings are Standard Model-like (so far). The prospects for discovering (and measuring) supersymmetry during future runs of the LHC are discussed in the frameworks of the constrained MSSM (CMSSM), models with non-universal soft supersymmetry-breaking contributions to Higgs masses (NUHM1,2) and the phenomenological MSSM with 10 arbitrary soft supersymmetry-breaking parameters (pMSSM10). In addition to the classic searches for missing transverse energy, searches for long-lived charged sparticles may also be promising. Read More

We explore the indirect sensitivities to decoupled new physics of prospective precision electroweak measurements, triple-gauge-coupling measurements and Higgs physics at future $e^+e^-$ colliders, with emphasis on the ILC250 and FCC-ee. The Standard Model effective field theory (SM EFT) is adopted as a model-independent approach for relating experimental precision projections to the scale of new physics, and we present prospective constraints on the Wilson coefficients of dimension-6 operators. We find that in a marginalised fit ILC250 EWPT measurements may be sensitive to new physics scales $\Lambda = \mathcal{O}(10)$~TeV, and FCC-ee EWPT measurements may be sensitive to $\Lambda = \mathcal{O}(30)$~TeV. Read More

We study supersymmetric scenarios in which the gluino is the next-to-lightest supersymmetric particle (NLSP), with a mass sufficiently close to that of the lightest supersymmetric particle (LSP) that gluino coannihilation becomes important. One of these scenarios is the MSSM with soft supersymmetry-breaking squark and slepton masses that are universal at an input GUT renormalization scale, but with non-universal gaugino masses. The other scenario is an extension of the MSSM to include vector-like supermultiplets. Read More

We consider two potential non-accelerator signatures of generalizations of the well-studied constrained minimal supersymmetric standard model (CMSSM). In one generalization, the universality constraints on soft supersymmetry-breaking parameters are applied at some input scale $M_{in}$ below the grand unification (GUT) scale $M_{GUT}$, a scenario referred to as `sub-GUT'. The other generalization we consider is to retain GUT-scale universality for the squark and slepton masses, but to relax universality for the soft supersymmetry-breaking contributions to the masses of the Higgs doublets. Read More

What life is there after Higgs? Specifically, what physics lies beyond the Standard Model (SM)? These are the biggest questions in particle physics today, and my talk is oriented towards efforts to answer them at the LHC and elsewhere. Read More

We reconsider a recently published algorithm (Dalkilic et al.) for merging lists by way of the perfect shuffle. The original publication gave only experimental results which, although consistent with linear execution time on the samples tested, provided no analysis. Read More

Supersymmetry is the most natural framework for physics above the TeV scale, and the corresponding framework for early-Universe cosmology, including inflation, is supergravity. No-scale supergravity emerges from generic string compactifications and yields a non-negative potential, and is therefore a plausible framework for constructing models of inflation. No-scale inflation yields naturally predictions similar to those of the Starobinsky model based on $R + R^2$ gravity, with a tilted spectrum of scalar perturbations: $n_s \sim 0. Read More

**Authors:**Jalal Abdallah, Henrique Araujo, Alexandre Arbey, Adi Ashkenazi, Alexander Belyaev, Joshua Berger, Celine Boehm, Antonio Boveia, Amelia Brennan, Jim Brooke, Oliver Buchmueller, Matthew Buckley, Giorgio Busoni, Lorenzo Calibbi, Sushil Chauhan, Nadir Daci, Gavin Davies, Isabelle De Bruyn, Paul De Jong, Albert De Roeck, Kees de Vries, Daniele Del Re, Andrea De Simone, Andrea Di Simone, Caterina Doglioni, Matthew Dolan, Herbi K. Dreiner, John Ellis, Sarah Eno, Erez Etzion, Malcolm Fairbairn, Brian Feldstein, Henning Flaecher, Eric Feng, Patrick Fox, Marie-Hélène Genest, Loukas Gouskos, Johanna Gramling, Ulrich Haisch, Roni Harnik, Anthony Hibbs, Siewyan Hoh, Walter Hopkins, Valerio Ippolito, Thomas Jacques, Felix Kahlhoefer, Valentin V. Khoze, Russell Kirk, Andreas Korn, Khristian Kotov, Shuichi Kunori, Greg Landsberg, Sebastian Liem, Tongyan Lin, Steven Lowette, Robyn Lucas, Luca Malgeri, Sarah Malik, Christopher McCabe, Alaettin Serhan Mete, Enrico Morgante, Stephen Mrenna, Yu Nakahama, Dave Newbold, Karl Nordstrom, Priscilla Pani, Michele Papucci, Sophio Pataraia, Bjoern Penning, Deborah Pinna, Giacomo Polesello, Davide Racco, Emanuele Re, Antonio Walter Riotto, Thomas Rizzo, David Salek, Subir Sarkar, Steven Schramm, Patrick Skubic, Oren Slone, Juri Smirnov, Yotam Soreq, Timothy Sumner, Tim M. P. Tait, Marc Thomas, Ian Tomalin, Christopher Tunnell, Alessandro Vichi, Tomer Volansky, Neal Weiner, Stephen M. West, Monika Wielers, Steven Worm, Itay Yavin, Bryan Zaldivar, Ning Zhou, Kathryn Zurek

**Category:**High Energy Physics - Phenomenology

This document outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both s-channel and t-channel scenarios. Read More

We discuss inflaton decays and reheating in no-scale Starobinsky-like models of inflation, calculating the effective equation-of-state parameter, $w$, during the epoch of inflaton decay, the reheating temperature, $T_{\rm reh}$, and the number of inflationary e-folds, $N_*$, comparing analytical approximations with numerical calculations. We then illustrate these results with applications to models based on no-scale supergravity and motivated by generic string compactifications, including scenarios where the inflaton is identified as an untwisted-sector matter field with direct Yukawa couplings to MSSM fields, and where the inflaton decays via gravitational-strength interactions. Finally, we use our results to discuss the constraints on these models imposed by present measurements of the scalar spectral index $n_s$ and the tensor-to-scalar perturbation ratio $r$, converting them into constraints on $N_*$, the inflaton decay rate and other parameters of specific no-scale inflationary models. Read More

The Higgs boson was postulated in 1964, and phenomenological studies of its possible production and decays started in the early 1970s, followed by studies of its possible production in electron-positron, antiproton-proton and proton-proton collisions, in particular. Until recently, the most sensitive searches for the Higgs boson were at LEP between 1989 and 2000, which were complemented by searches at the Fermilab Tevatron. Then the LHC experiments ATLAS and CMS entered the hunt, announcing on July 4, 2012 the discovery of a "Higgs-like" particle with a mass of about 125~GeV. Read More

What is the Higgs boson telling us? What else is there, maybe supersymmetry and/or dark matter? How do we find it? These are now the big questions in collider physics that I discuss in this talk, from a personal point of view. Read More

We develop a universal approach to the one-loop effective field theory (EFT) using the Covariant Derivative Expansion (CDE) method. We generalise previous results to include broader classes of UV models, showing how expressions previously obtained assuming degenerate heavy-particle masses can be extended to non-degenerate cases. We apply our method to the general MSSM with non-degenerate stop squarks, illustrating our approach with calculations of the coefficients of dimension-6 operators contributing to the $hgg$ and $h\gamma\gamma$ couplings, and comparing with exact calculations of one-loop Feynman diagrams. Read More

We discuss phenomenological aspects of no-scale supergravity inflationary models motivated by compactified string models, in which the inflaton may be identified either as a K\"ahler modulus or an untwisted matter field, focusing on models that make predictions for the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$ that are similar to the Starobinsky model. We discuss possible patterns of soft supersymmetry breaking, exhibiting examples of the pure no-scale type $m_0 = B_0 = A_0 = 0$, of the CMSSM type with universal $A_0$ and $m_0 \ne 0$ at a high scale, and of the mSUGRA type with $A_0 = B_0 + m_0$ boundary conditions at the high input scale. These may be combined with a non-trivial gauge kinetic function that generates gaugino masses $m_{1/2} \ne 0$, or one may have a pure gravity mediation scenario where trilinear terms and gaugino masses are generated through anomalies. Read More

Some variants of the MSSM feature a strip in parameter space where the lightest neutralino is identified as the lightest supersymmetric particle (LSP), the gluino is the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with the LSP, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP. We calculate the relic density along this gluino coannihilation strip in the MSSM, including the effects of gluino-gluino bound states and initial-state Sommerfeld enhancement, and taking into account the decoupling of the gluino and LSP densities that occurs for large values of the squark mass. We find that bound-state effects can increase the maximum LSP mass for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ~ 50% if the squark to gluino mass ratio is 1. Read More

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. Read More

Run 2 of the LHC offers some beautiful prospects for new physics, including flavour physics as well as more detailed studies of the Higgs boson and searches for new physics beyond the Standard Model (BSM). One of the possibilities for BSM physics is supersymmetry, and flavour physics plays various important r\^oles in constraining supersymmetric models. Read More

We analyse the prospects for constructing hybrid models of inflation that provide a dynamical realisation of the apparent closeness between the supersymmetric GUT scale and the possible scale of cosmological inflation. In the first place, we consider models based on the flipped SU(5)$\times$U(1) gauge group, which has no magnetic monopoles. In one model, the inflaton is identified with a sneutrino field, and in the other model it is a gauge singlet. Read More