arXiv subjects

John Terning

Publications and source records attributed to John Terning.

At least 55 records · Page 3Linked to original sources

arXiv2014

Planck Data and Ultralight Axions

We examine the effects of photon-axion mixing on the CMB. We show that if there are very underdense regions between us and the last scattering surface which contain coherent magnetic fields (whose strength can be orders of magnitude weaker than the current bounds), then photon-axion mixing can induce observable deviations in the CMB spectrum. Specifically, we show that the mixing can give rise to non-thermal spots on the CMB sky. As an example we consider the well known CMB cold spot, which according to the Planck data has a weak distortion from a black body spectrum, that can be fit by our model. While this explanation of the non-thermality in the region of the cold spot is quite intriguing, photon-axion oscillation do not explain the temperature of the cold spot itself. Nevertheless we demonstrate the possible sensitivity of the CMB to ultralight axions which could be exploited by observers.

astro-ph.CO↗

arXiv2013

Composite Higgs Sketch

The coupling of a composite Higgs to the standard model fields can deviate substantially from the standard model values. In this case perturbative unitarity might break down before the scale of compositeness is reached, which would suggest that additional composites should lie well below this scale. In this paper we account for the presence of an additional spin 1 custodial triplet of rhos. We examine the implications of requiring perturbative unitarity up to the compositeness scale and find that one has to be close to saturating certain unitarity sum rules involving the Higgs and the rho couplings. Given these restrictions on the parameter space we investigate the main phenomenological consequences of the spin 1 triplet. We find that they can substantially enhance the Higgs di-photon rate at the LHC even with a reduced Higgs coupling to gauge bosons. The main existing LHC bounds arise from di-boson searches, especially in the experimentally clean channel where the charged rhos decay to a W-boson and a Z, which then decay leptonically. We find that a large range of interesting parameter space with 700 GeV < m(rho) < 2 TeV is currently experimentally viable.

hep-ph↗

arXiv2013

A Higgslike Dilaton

We examine the possibility that the recently discovered 125 GeV higgs like resonance actually corresponds to a dilaton: the Goldstone boson of scale invariance spontaneously broken at a scale f. Comparing to LHC data we find that a dilaton can reproduce the observed couplings of the new resonance as long as f ~ v, the weak scale. This corresponds to the dynamical assumption that only operators charged under the electroweak gauge group obtain VEVs. The more difficult task is to keep the mass of the dilaton light compared to the dynamical scale, Lambda ~ 4 pi f, of the theory. In generic, non-supersymmetric theories one would expect the dilaton mass to be similar to Lambda. The mass of the dilaton can only be lowered at the price of some percent level (or worse) tuning and/or additional dynamical assumptions: one needs to suppress the contribution of the condensate to the vacuum energy (which would lead to a large dilaton quartic coupling), and to allow only almost marginal deformations of the CFT.

hep-ph↗

arXiv2012

Constraining the Unhiggs with LHC data

Recent measurements by the ATLAS and CMS experiments have excluded the Standard Model Higgs boson in the high mass region, even if it is produced with a significantly smaller cross section than expected. The bounds are dominated by the non-observation of a signal in the clean gold-plated mode $h\to ZZ\to 4\ell$ and, hence, are directly related to the special role of the Higgs in electroweak symmetry breaking. A smaller cross section in comparison to the Standard Model is expected if the Higgs is realized as an unparticle in the Unhiggs scenario. With the LHC probing $σ/σ^{SM}<1$, we can therefore reinterpret the $h\to ZZ\to 4\ell$ exclusion limits as bounds on the Unhiggs' scaling dimension. Throughout the high Higgs mass range, where we expect a large signal in the presence of the Standard Model Higgs for the 2011 ATLAS and CMS data sets, the observed limits translate into mild bounds on the Unhiggs scaling dimension in the high mass region.

hep-ph↗

arXiv2012

Unconstraining the Unhiggs

We investigate whether or not perturbative unitarity is preserved in the Unhiggs model for the scattering process of heavy quarks and longitudinal gauge bosons $\bar q q \to V_L^+ V_L^-$. With the Yukawa coupling given in the original formulation of the Unhiggs model, the model preserves unitarity for Unhiggs scaling dimensions $d\leq 1.5$. We examine the LHC phenomenology that is implied by the Unhiggs model in this parameter range in detail and discuss to what extent the LHC can test $d$ if an excess is measured in the phenomenologically clean $ZZ$ channel in the future or if the LHC measurement remains consistent with the background. We then make use of the AdS/CFT correspondence to derive a new Yukawa coupling that is conformally invariant at high energies, and show that with this Yukawa coupling the theory is unitary for $1 \leq d < 2$.

hep-ph↗

arXiv2012

Supersymmetry Breaking Triggered by Monopoles

We investigate N = 1 supersymmetric gauge theories where monopole condensation triggers supersymmetry breaking in a metastable vacuum. The low-energy effective theory is an O'Raifeartaigh-like model of the kind investigated recently by Shih where the R-symmetry can be spontaneously broken. We examine several implementations with varying degrees of phenomenological interest.

hep-th↗

arXiv2012

Light Stops from Seiberg Duality

If low-energy supersymmetry is realized in nature, a seemingly contrived hierarchy in the squark mass spectrum appears to be required. We show that composite supersymmetric theories at the bottom of the conformal window can automatically yield the spectrum that is suggested by experimental data and naturalness. With a non-tuned choice of parameters, the only superpartners below one TeV will be the partners of the Higgs, the electroweak gauge bosons, the left-handed top and bottom, and the right-handed top, which are precisely the particles needed to make weak scale supersymmetry breaking natural. In the model considered here, these correspond to composite (or partially composite) degrees of freedom via Seiberg duality, while the other MSSM fields, with their heavier superpartners, are elementary. The key observation is that at or near the edge of the conformal window, soft supersymmetry breaking scalar and gaugino masses are transmitted only to fundamental particles at leading order. With the potential that arises from the duality, a Higgs with a 125 GeV mass, with nearly SM production rates, is naturally accommodated without tuning. The lightest ordinary superpartner is either the lightest stop or the lightest neutralino. If it is the stop, it is natural for it to be almost degenerate with the top, in which case it decays to top by emitting a very soft gravitino, making it quite difficult to find this mode at the LHC and more challenging to find SUSY in general, yielding a simple realization of the stealth supersymmetry idea. We analyze four benchmark spectra in detail.

hep-ph↗

arXiv2011

A Seiberg Dual for the MSSM: Partially Composite W and Z

We examine the possibility that the SU(2) gauge group of the standard model appears as the dual "magnetic" gauge group of a supersymmetric gauge theory, thus the W and Z (and through mixing, the photon) are composite (or partially composite) gauge bosons. Fully composite gauge bosons are expected to interact strongly at the duality scale, and a large running is needed to match the electroweak gauge couplings. Alternatively one can mix the composite "magnetic" gauge bosons with some elementary ones to obtain realistic models. In the simplest and most compelling example the Higgs and top are composite, the W and Z partially composite and the light fermions elementary. The effective theory is an NMSSM-type model where the singlet is a component of the composite meson. There is no little hierarchy problem and the Higgs mass can be as large as 400 GeV. This "fat Higgs"-like model can be considered as an explicit 4D implementation of RS-type models with gauge fields in the bulk.

hep-ph↗

arXiv2011

SUSY Hidden in the Continuum

We study models where the superpartners of the ordinary particles have continuous spectra rather than being discrete states, which can occur when the supersymmetric standard model is coupled to an approximately conformal sector. We show that when superpartners that are well into the continuum are produced at a collider they tend to have long decay chains that step their way down through the continuum, emitting many fairly soft standard model particles along the way, with a roughly spherical energy distribution in the center of mass frame.

hep-ph↗

arXiv2010

Constraints on the Unhiggs Model from Top Quark Decay

We compute the top quark decay rate in the Unhiggs model. In this model, the longitudinally polarized W's are unparticles, owing to their Goldstone boson nature, while the transversely polarized W's are not. Thus the fraction of decays with a longitudinal W emitted is different than in the Standard Model. Comparing this calculation to CDF data, we are able to rule out some of the Unhiggs model parameter space. We also use the expected increased accuracy of top decay measurements at the LHC to anticipate further constraints on the Unhiggs.

hep-ph↗

arXiv2010

Electroweak Symmetry Breaking From Monopole Condensation

We examine models where massless chiral fermions with both "electric" and "magnetic" hypercharges could form condensates. When some of the fermions are also electroweak doublets such condensates can break the electroweak gauge symmetry down to electromagnetism in the correct way. Since ordinary hypercharge is weakly coupled at the TeV scale, magnetic hypercharge is strongly coupled and can potentially drive the condensation. Such models are similar to technicolor, but with hypercharge playing the role of the technicolor gauge group, so the standard model gauge group breaks itself. A heavy top mass can be generated via the Rubakov-Callan effect and could thus decouple the scale of flavor physics from the electroweak scale.

hep-ph↗

arXiv2010

Anomaly Constraints on Monopoles and Dyons

Fermions with magnetic charges can contribute to anomalies. We derive the axial anomaly and gauge anomalies for monopoles and dyons, and find eight new gauge anomaly cancelation conditions in a general theory with both electric and magnetic charges. As a byproduct we also extend the Zwanziger two-potential formalism to include the theta parameter, and elaborate on the condition for CP invariance in theories with fermionic dyons.

hep-th↗

arXiv2009

The Unhiggs

We examine a scenario where the Higgs is part of an approximate conformal field theory, and has a scaling dimension greater than one. Such an unparticle Higgs (or Unhiggs) can still break electroweak symmetry and unitarize WW scattering, but its gauge couplings are suppressed. An Unhiggs model has a reduced sensitivity of the weak scale to the cutoff, and can thus provide a solution to the little hierarchy problem.

hep-ph↗

arXiv2009

Continuum Superpartners from Supersymmetric Unparticles

We examine supersymmetric theories with approximately conformal sectors. Without an IR cutoff the theory has a continuum of modes, which are often referred to as "unparticles." Making use of the AdS/CFT correspondence we find that in the presence of a soft-wall, a gap in the spectrum can arise, separating the zero-modes from the continuum modes. In some cases there are also discrete massive levels in the gap. We also show that when supersymmetry is broken the superpartner of a quark or lepton may simply be a bosonic continuum above a gap. Such extensions of the standard model have novel signatures at the LHC.

hep-ph↗

arXiv2009

Quirky Composite Dark Matter

We propose a new dark matter candidate, quirky dark matter, that is a scalar baryonic bound state of a new non-Abelian force that becomes strong below the electroweak scale. The bound state is made of chiral quirks: new fermions that transform under both the new strong force as well as in a chiral representation of the electroweak group, acquiring mass from the Higgs mechanism. Electric charge neutrality of the lightest baryon requires approximately degenerate quirk masses which also causes the charge radius of the bound state to be negligible. The abundance is determined by an asymmetry that is linked to the baryon and lepton numbers of the universe through electroweak sphalerons. Dark matter elastic scattering with nuclei proceeds through Higgs exchange as well as an electromagnetic polarizability operator which is just now being tested in direct detection experiments. A novel method to search for quirky dark matter is to look for a gamma-ray dark line spectroscopic feature in galaxy clusters that result from the quirky Lyman-alpha or quirky hyperfine transitions. Colliders are expected to dominantly produce quirky mesons, not quirky baryons, consequently large missing energy is not the primary collider signal of the physics associated with quirky dark matter.

hep-ph↗

arXiv2009

Gaugephobic Higgs Signals at the LHC

The Gaugephobic Higgs model provides an interpolation between three different models of electroweak symmetry breaking: Higgsless models, Randall-Sundrum models, and the Standard Model. At parameter points between the extremes, Standard Model Higgs signals are present at reduced rates, and Higgsless Kaluza-Klein excitations are present with shifted masses and couplings, as well as signals from exotic quarks necessary to protect the Zbb coupling. Using a new implementation of the model in SHERPA, we show the LHC signals which differentiate the generic Gaugephobic Higgs model from its limiting cases. These are all signals involving a Higgs coupling to a Kaluza-Klein gauge boson or quark. We identify the clean signal $p p \to W^(i) \to W H$ mediated by a Kaluza-Klein W, which can be present at large rates and is enhanced for even Kaluza-Klein numbers. Due to the very hard lepton coming from the W decay, this signature has little background, and provides a better discovery channel for the Higgs than any of the Standard Model modes, over its entire mass range. A Higgs radiated from new heavy quarks also has large rates, but is much less promising due to very high multiplicity final states.

hep-ph↗

arXiv2009

A Quirky Little Higgs Model

We consider an extra dimensional model where the quadratically divergent top loop contribution to the Higgs mass is cancelled by an uncolored heavy "top quirk" charged under a different SU(3) gauge group. The cancellation is enforced by bulk gauge symmetries. Thus we have an unusual type of little Higgs model which has some quirky signatures. The top partner in this model could be identified at the Large Hadron Collider due to macroscopic strings that connect quirk and anti-quirks. The model can undergo radiative electroweak symmetry breaking and is consistent with precision electroweak measurements.

hep-ph↗

arXiv2008

The AdS/QCD Correspondence: Still Undelivered

We consider the particle spectrum and event shapes in large N gauge theories in different regimes of the short-distance 't Hooft coupling, lambda. The mesons in the small lambda limit should have a Regge spectrum in order to agree with perturbation theory, while generically the large lambda theories with gravity duals produce spectra reminiscent of KK modes. We argue that these KK-like states are qualitatively different from QCD modes: they are deeply bound states which are sensitive to short distance interactions rather than the flux tube-like states expected in asymptotically free, confining gauge theories. In addition, we also find that the characteristic event shapes for the large lambda theories with gravity duals are close to spherical, very different from QCD-like (small lambda, small N) and Nambu-Goto-like (small lambda, large N) theories which have jets. This observation is in agreement with the conjecture of Strassler on event shapes in large 't Hooft coupling theories, which was recently proved by Hofman and Maldacena for the conformal case. This conclusion does not change even when considering soft-wall backgrounds in the gravity dual. The picture that emerges is the following: theories with small and large lambda are qualitatively different, while theories with small and large N are qualitatively similar. Thus it seems that it is the relative smallness of the 't Hooft coupling in QCD that prevents a reliable AdS/QCD correspondence from emerging, and that reproducing characteristic QCD-like behavior will require genuine stringy dynamics to be incorporated into any putative dual theory.

hep-ph↗