We consider both "bottom-up" and "top-down" approaches to the origin of gauge kinetic mixing. We focus on the possibilities for obtaining kinetic mixings ε which are consistent with experimental ...constraints and are much smaller than the naive estimates ( ε ∼ 10−2 – 10−1) at the one-loop level. In the bottom-up approach, we consider the possible suppression from multiloop processes. Indeed we argue that kinetic mixing through gravity alone, requires at least six loops and could be as large as ∼ 10−13. In the top-down approach we consider embedding the Standard Model and a U (1)X in a single grand-unified gauge group as well as the mixing between Abelian and non-Abelian gauge sectors.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Warm dark matter cosmologies have been widely studied as an alternative to the cold dark matter paradigm, the characteristic feature being a suppression of structure formation on small cosmological ...scales. A very similar situation occurs if standard cold dark matter particles are kept in local thermal equilibrium with a, possibly dark, relativistic species until the Universe has cooled down to keV temperatures. We perform a systematic phenomenological study of this possibility, and classify all minimal models containing dark matter and an arbitrary radiation component that allows such a late kinetic decoupling. We recover explicit cases recently discussed in the literature and identify new classes of examples that are very interesting from a model-building point of view. In some of these models dark matter is inevitably self-interacting, which is remarkable in view of recent observational support for this possibility. Hence, dark matter models featuring late kinetic decoupling have the potential not only to alleviate the missing satellites problem but also to address other problems of the cosmological concordance model on small scales, in particular the cusp-core and too-big-too-fail problems, in some cases without invoking any additional input.
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We study particle decay as the origin of dark radiation. After elaborating general properties and useful parametrisations we provide model-independent and easy-to-use constraints from ...nucleosynthesis, the cosmic microwave background and structure formation. Bounds on branching ratios and mass hierarchies depend in a unique way on the time of decay. We demonstrate their power to exclude well-motivated scenarios taking the example of the lightest ordinary sparticle decaying into the gravitino. We point out signatures and opportunities in cosmological observations and structure formation. For example, if there are two dark decay modes, dark radiation and the observed dark matter with adjustable free-streaming can originate from the same decaying particle, solving small-scale problems of structure formation. Hot dark matter mimicking a neutrino mass scale as deduced from cosmological observations can arise and possibly be distinguished after a discovery. Our results can be used as a guideline for model building.
Beyond cuts in small signal scenarios Alvestad, Daniel; Fomin, Nikolai; Kersten, Jörn ...
The European physical journal. C, Particles and fields,
05/2023, Volume:
83, Issue:
5
Journal Article
Peer reviewed
Open access
We investigate enhancing the sensitivity of new physics searches at the LHC by machine learning in the case of background dominance and a high degree of overlap between the observables for signal and ...background. We use two different models, XGBoost and a deep neural network, to exploit correlations between observables and compare this approach to the traditional cut-and-count method. We consider different methods to analyze the models' output, finding that a template fit generally performs better than a simple cut. By means of a Shapley decomposition, we gain additional insight into the relationship between event kinematics and the machine learning model output. We consider a supersymmetric scenario with a metastable sneutrino as a concrete example, but the methodology can be applied to a much wider class of models.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
7.
Trilinear-augmented gaugino mediation Heisig, Jan; Kersten, Jörn; Murphy, Nick ...
The journal of high energy physics,
05/2017, Volume:
2017, Issue:
5
Journal Article
Peer reviewed
Open access
A
bstract
We consider a gaugino-mediated supersymmetry breaking scenario where in addition to the gauginos the Higgs fields couple directly to the field that breaks supersymmetry. This yields ...non-vanishing trilinear scalar couplings in general, which can lead to large mixing in the stop sector providing a sufficiently large Higgs mass. Using the most recent release of F
eyn
H
iggs
, we show the implications on the parameter space. Assuming a gravitino LSP, we find allowed points with a neutralino, sneutrino or stau NLSP. We test these points against the results of Run 1 of the LHC, considering in particular searches for heavy stable charged particles.
Supernova neutrinos have several exceptional features which can lead to interesting physical consequences. At the production point their wave packets have an extremely small size
σ
x
∼
10
-
11
cm; ...hence the energy uncertainty can be as large as the energy itself,
σ
E
∼
E
, and the coherence length is short. On the way to the Earth the wave packets of mass eigenstates spread to macroscopic sizes and separate. Inside the Earth the mass eigenstates split into eigenstates in matter and oscillate again. The coherence length in the Earth is comparable with the radius of the Earth. We explore these features and their consequences. (1) We present new estimates of the wave packet size. (2) We consider the decoherence condition for the case of wave packets with spatial spread and show that it is not modified by the spread. (3) We study the coherence of neutrinos propagating in a multi-layer medium with density jumps at the borders of layers. In this case coherence can be partially restored due to a “catch-up effect”, increasing the coherence length beyond the usual estimate. This catch-up effect can occur for supernova neutrinos as they cross the shock wave fronts in the exploding star or the core of the Earth.
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We re-derive the renormalization group equation for the effective coupling of the dimension five operator which corresponds to a Majorana mass matrix for the Standard Model neutrinos. We find a ...result which differs somewhat from earlier calculations, leading to modifications in the evolution of leptonic mixing angles and CP phases. We also present a general method for calculating β-functions from counterterms in MS-like renormalization schemes, which works for tensorial quantities.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Despite the astonishing success of standard LambdaCDM cosmology, there is mounting evidence for a tension with observations at small and intermediate scales. We introduce a simple model where both ...cold dark matter (DM) and sterile neutrinos are charged under a new U(1)X gauge interaction. The resulting DM self-interactions resolve the tension with the observed abundances and internal density structures of dwarf galaxies. At the same time, the sterile neutrinos can account for both the small hot DM component favored by cosmological observations and the neutrino anomalies found in short-baseline experiments.
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