arXiv subjects

Mads T. Frandsen

Publications and source records attributed to Mads T. Frandsen.

At least 37 records · Page 2Linked to original sources

arXiv2016

Asymmetric Dark Matter Models and the LHC Diphoton Excess

The existence of dark matter (DM) and the origin of the baryon asymmetry are persistent indications that the SM is incomplete. More recently, the ATLAS and CMS experiments have observed an excess of diphoton events with invariant mass of about 750 GeV. One interpretation of this excess is decays of a new spin-0 particle with a sizable diphoton partial width, e.g. induced by new heavy weakly charged particles. These are also key ingredients in models cogenerating asymmetric DM and baryons via sphaleron interactions and an initial particle asymmetry. We explore what consequences the new scalar may have for models of asymmetric DM that attempt to account for the similarity of the dark and visible matter abundances.

hep-ph↗

arXiv2016

Symmetries and composite dynamics for the 750 GeV diphoton excess

The ATLAS and CMS experiments at LHC observe small excesses of diphoton events with invariant mass around 750 GeV. Here we study the possibility of nearly parity degenerate and vector-scalar degenerate spectra as well as composite dynamics in 2 scenarios for explaining the excess: Production of a pseudo-scalar via gluon or photon fusion or via decay of a parent particle together with soft additional final states. We discuss possible underlying realizations of the scenarios motivated by dynamical models of electroweak symmetry breaking (without new coloured states) and fermion masses.

hep-ph↗

arXiv2015

Diboson Signals via Fermi Scale Spin-One States

ATLAS and CMS observe deviations from the expected background in diboson invariant mass searches of new resonances around 2 TeV. We provide a general analysis of the results in terms of spin-one resonances and find that Fermi scale composite dynamics can be the culprit. The analysis and methodology can be employed for future searches at run two of the Large Hadron Collider.

hep-ph↗

arXiv2015

New or $ν$ Missing Energy? Discriminating Dark Matter from Neutrino Interactions at the LHC

Missing energy signals such as monojets are a possible signature of Dark Matter (DM) at colliders. However, neutrino interactions beyond the Standard Model may also produce missing energy signals. In order to conclude that new "missing particles" are observed the hypothesis of BSM neutrino interactions must be rejected. In this paper, we first derive new limits on these Non-Standard neutrino Interactions (NSIs) from LHC monojet data. For heavy NSI mediators, these limits are much stronger than those coming from traditional low-energy $ν$ scattering or $ν$ oscillation experiments for some flavor structures. Monojet data alone can be used to infer the mass of the "missing particle" from the shape of the missing energy distribution. In particular, 13 TeV LHC data will have sensitivity to DM masses greater than $\sim$ 1 TeV. In addition to the monojet channel, NSI can be probed in multi-lepton searches which we find to yield stronger limits at heavy mediator masses. The sensitivity offered by these multi-lepton channels provide a method to reject or confirm the DM hypothesis in missing energy searches.

hep-ph↗

arXiv2015

Custodial Vector Model

We analyze the Large Hadron Collider (LHC) phenomenology of heavy vector resonances with a $SU(2)_L\times SU(2)_R$ spectral global symmetry. This symmetry partially protects the electroweak S-parameter from large contributions of the vector resonances. The resulting custodial vector model spectrum and interactions with the standard model fields lead to distinct signatures at the LHC in the diboson, dilepton and associated Higgs channels.

hep-ph↗

arXiv2015

Unitarity implications of diboson resonance in the TeV region for Higgs physics

We investigate the implications of a putative new resonance in the TeV region coupled to the weak bosons. By studying perturbative unitarity in longitudinal WW scattering, we find that a weakly coupled spin-1 resonance, that explains the ATLAS diboson excesses, is allowed with a SM-like Higgs. On the other hand, larger values of the resonance couplings, preferred in models of strong dynamics, would imply either sizeable reduction of the Higgs couplings or new physics, beyond the diboson resonance, at a few TeV.

hep-ph↗

arXiv2015

On the Direct Detection of Dark Matter Annihilation

We investigate the direct detection phenomenology of a class of dark matter (DM) models in which DM does not directly interact with nuclei, {but rather} the products of its annihilation do. When these annihilation products are very light compared to the DM mass, the scattering in direct detection experiments is controlled by relativistic kinematics. This results in a distinctive recoil spectrum, a non-standard and or even absent annual modulation, and the ability to probe DM masses as low as a $\sim$10 MeV. We use current LUX data to show that experimental sensitivity to thermal relic annihilation cross sections has already been reached in a class of models. Moreover, the compatibility of dark matter direct detection experiments can be compared directly in $E_{\rm min}$ space without making assumptions about DM astrophysics, mass, or scattering form factors. Lastly, when DM has direct couplings to nuclei, the limit from annihilation to relativistic particles in the Sun can be stronger than that of conventional non-relativistic direct detection by more than three orders of magnitude for masses in a 2-7 GeV window.

hep-ph↗

arXiv2014

Halo Independent Direct Detection of Momentum-Dependent Dark Matter

We show that the momentum dependence of dark matter interactions with nuclei can be probed in direct detection experiments without knowledge of the dark matter velocity distribution. This is one of the few properties of DM microphysics that can be determined with direct detection alone, given a signal of dark matter in multiple direct detection experiments with different targets. Long-range interactions arising from the exchange of a light mediator are one example of momentum-dependent DM. For data produced from the exchange of a massless mediator we find for example that the mediator mass can be constrained to be $\lesssim 10$ MeV for DM in the 20-1000 GeV range in a halo-independent manner.

hep-ph↗

arXiv2014

LUX Constraints on Magnetic Dark Matter in the $S\bar{E} χ$y Model with(out) Naturality

We study phenomenological constraints in a simple $S\bar{E} χ$y extension of the Standard Model (SM) with a 125 GeV Higgs, a vector-like heavy electron $(E)$, a complex scalar electron $(S)$ and a standard model singlet Dirac fermion $(χ)$. The interactions among the dark matter candidate $χ$ and the standard model particles occur via loop-induced processes involving the Yukawa interaction $S\bar{E} χ$y. The model is an explicit perturbative realization of so-called magnetic dark matter. The field content allows for a cancelation of quadratic divergences in the scalar masses at one-loop, a phenomenon which we refer to as perturbative naturality. The basic model is constrained dominantly by direct detection experiments and its parameter space can be nearly entirely covered by up-coming ton-scale direct detection experiments. We conclude this work by discussing different variations of the model.

hep-ph↗

arXiv2014

The Up-Shot of Inelastic Down-Scattering at CDMS-Si

We study dark matter that inelastically scatters and de-excites in direct detection experiments, as an interpretation of the CDMS-Si events in light of the recent LUX data. The constraints from LUX and XENON10 require the mass-splitting between the DM excited and de-excited states to be $|δ| \gtrsim 50$ keV. At the same time, the CDMS-Si data itself do not allow for a consistent DM interpretation for mass splittings larger than $|δ| \sim $200 keV. We find that a low threshold analysis will be needed to rule out this interpretation of the CDMS-Si events. In a simple model with a kinetically mixed dark photon, we show that the CDMS-Si rate and the thermal relic abundance can both be accommodated.

hep-ph↗

arXiv2014

Colliding clusters and dark matter self-interactions

When a dark matter halo moves through a background of dark matter particles, self-interactions can lead to both deceleration and evaporation of the halo and thus shift its centroid relative to the collisionless stars and galaxies. We study the magnitude and time evolution of this shift for two classes of dark matter self-interactions, viz. frequent self-interactions with small momentum transfer (e.g. due to long-range interactions) and rare self-interactions with large momentum transfer (e.g. contact interactions), and find important differences between the two cases. We find that neither effect can be strong enough to completely separate the dark matter halo from the galaxies, if we impose conservative bounds on the self-interaction cross-section. The majority of both populations remain bound to the same gravitational potential and the peaks of their distributions are therefore always coincident. Consequently any apparent separation is mainly due to particles which are leaving the gravitational potential, so will be largest shortly after the collision but not observable in evolved systems. Nevertheless the fraction of collisions with large momentum transfer is an important characteristic of self-interactions, which can potentially be extracted from observational data and provide an important clue as to the nature of dark matter.

astro-ph.CO↗

arXiv2013

The Technicolor Higgs in the Light of LHC Data

We consider scenarios in which the 125 GeV resonance observed at the Large Hadron Collider is a Technicolor (TC) isosinglet scalar, the TC Higgs. By comparison with quantum chromodynamics, we argue that the couplings of the TC Higgs to the massive weak bosons are very close to the Standard Model (SM) values. The couplings to photons and gluons are model-dependent, but close to the SM values in several TC theories. The couplings of the TC Higgs to SM fermions are due to interactions beyond TC, such as Extended Technicolor: if such interactions successfully generate mass for the SM fermions, we argue that the couplings of the latter to the TC Higgs are also SM-like. We suggest a generic parameterization of the TC Higgs interactions with SM particles that accommodates a large class of TC models, and we perform a fit of these parameters to the Higgs LHC data. The fit reveals regions of parameter space where the form factors are of order unity and consistent with data at the 95% CL, in agreement with expectations in TC theories. This indicates that the discovered Higgs boson is consistent with the TC Higgs hypothesis for several TC theories.

hep-ph↗

arXiv2013

The unbearable lightness of being: CDMS versus XENON

The CDMS-II collaboration has reported 3 events in a Si detector, which are consistent with being nuclear recoils due to scattering of Galactic dark matter particles with a mass of about 8.6 GeV and a cross-section on neutrons of about 2 x 10^-41 cm^2. While a previous result from the XENON10 experiment has supposedly ruled out such particles as dark matter, we find by reanalysing the XENON10 data that this is not the case. Some tension remains however with the upper limit placed by the XENON100 experiment, independently of astrophysical uncertainties concerning the Galactic dark matter distribution. We explore possible ways of ameliorating this tension by altering the properties of dark matter interactions. Nevertheless, even with standard couplings, light dark matter is consistent with both CDMS and XENON10/100.

hep-ph↗

arXiv2013

125 GeV Higgs from a not so light Technicolor Scalar

Assuming that the observed Higgs-like resonance at the Large Hadron Collider is a technicolor isosinglet scalar (the technicolor Higgs), we argue that the standard model top-induced radiative corrections reduce its dynamical mass towards the desired experimental value. We then discuss conditions for the spectrum of technicolor theories to feature a technicolor Higgs with the phenomenologically required dynamical mass. We use scaling laws coming from modifying the technicolor matter representation, number of technicolors, techniflavors as well as the number of doublets gauged under the electroweak theory. Finally we briefly summarize the potential effects of walking dynamics on the technicolor Higgs.

hep-ph↗

arXiv2013

Perturbative extension of the standard model with a 125 GeV Higgs and Magnetic Dark Matter

We introduce a perturbative extension of the standard model featuring a new dark matter sector together with a 125 GeV Higgs. The new sector consists of a vector-like heavy electron E, a complex scalar electron S and a standard model singlet Dirac fermion χ. The interactions among the dark matter candidate χand the standard model particles occur via loop-induced processes involving the operator SEχy, with y being the Yukawa-like coupling. The model is an explicit underlying realization of the light magnetic dark matter effective model introduced earlier to alleviate the tension among several direct dark matter search experiments. We further constrain the parameters of the underlying theory using results from the Large Hadron Collider. The extension can accommodate the recently observed properties of the Higgs-like state and leads to interesting predictions. Finally we show that the model's collider phenomenology and constraints nicely complement the ones coming from dark matter searches.

hep-ph↗

arXiv2012

Loop-induced dark matter direct detection signals from gamma-ray lines

Improved limits as well as tentative claims for dark matter annihilation into gamma-ray lines have been presented recently. We study the direct detection cross section induced from dark matter annihilation into two photons in a model-independent fashion, assuming no additional couplings between dark matter and nuclei. We find a striking non-standard recoil spectrum due to different destructively interfering contributions to the dark matter nucleus scattering cross section. While in the case of s-wave annihilation the current sensitivity of direct detection experiments is insufficient to compete with indirect detection searches, for p-wave annihilation the constraints from direct searches are comparable. This will allow to test dark matter scenarios with p-wave annihilation that predict a large di-photon annihilation cross section in the next generation of experiments.

hep-ph↗

arXiv2012

Light Higgs from Scalar See-Saw in Technicolor

We consider a TeV scale see-saw mechanism leading to light scalar resonances in models with otherwise intrinsically heavy scalars. The mechanism can provide a 125 GeV technicolor Higgs in e.g. two-scale TC models

hep-ph↗

arXiv2012

LHC and Tevatron bounds on the dark matter direct detection cross-section for vector mediators

We study the interactions of a new spin-1 mediator that connects the Standard Model to dark matter. We constrain its decay channels using monojet and monophoton searches, as well as searches for resonances in dijet, dilepton and diboson final states including those involving a possible Higgs. We then interpret the resulting limits as bounds on the cross-section for dark matter direct detection without the need to specify a particular model. For mediator masses between 300 and 1000 GeV these bounds are considerably stronger than the ones obtained under the assumption that the mediator can be integrated out.

hep-ph↗