A
bstract
We investigate the stability of the electroweak vacuum for two-Higgs-doublet models with a supersymmetric UV completion. The supersymmetry breaking scale is taken to be of the order of the ...grand unification scale. We first study the case where all superpartners decouple at this scale. We show that contrary to the Standard Model with one Higgs doublet, matching to the supersymmetric UV completion is possible if the low-scale model contains two Higgs doublets. In this case vacuum stability and experimental constraints point towards low values of tan
β
≲ 2 and pseudoscalar masses of at least about a TeV. If the higgsino superpartners of the Higgs fields are also kept light, the conclusions are similar and essentially independent of the higgsino mass. Finally, if all gauginos are also given electroweak-scale masses (split supersymmetry with two Higgs doublets), the model cannot be matched to supersymmetry at very high scales when requiring a 125 GeV Higgs. Light neutral and charged higgsinos therefore emerge as a promising signature of a supersymmetric UV completion of the Standard Model at the grand unification scale.
A
bstract
In some models of thermal relic dark matter, the relic abundance may be set by inelastic scattering processes (rather than annihilations) becoming inefficient as the universe cools down. ...This effect has been called coscattering. We present a procedure to numerically solve the full momentum-dependent Boltzmann equations in coscattering, which allows for a precise calculation of the dark matter relic density including the effects of early kinetic decoupling. We apply our method to a simple model, containing a fermionic SU(2) triplet and a fermionic singlet with electroweak-scale masses, at small triplet-singlet mixing. The relic density can be set by either coannihilation or, at values of the mixing angle
θ
≲ 10
−
5
, by coscattering. We identify the parameter ranges which give rise to the observed relic abundance. As a special case, we study bino-like dark matter in split supersymmetry at large
μ
.
Tardigrades can survive harsh environmental conditions, such as drought and low temperature. To withstand freezing, they enter cryobiosis, a state of biological organization in which metabolic ...activity slows down or comes reversibly to a standstill. Thus, cryobiosis resembles anhydrobiosis, where tardigrades (and a few other invertebrate groups) undergo extreme desiccation and appear not to age in the dry state. The lack of ageing in the anhydrobiotic state, the so‐called ‘Sleeping Beauty’ hypothesis, is assumed also to pertain to cryobiosis, but this has not been investigated. To test this, a group of tardigrades was subjected to sub‐zero temperature treatment by alternating weekly periods of freezing at −30°C and feeding at 20°C. The temporarily frozen tardigrades lived twice as long as the control group, but both control and temporarily frozen groups had similar lifespans if the time spent frozen was excluded. This represents the first demonstration that the ‘Sleeping Beauty’ hypothesis applies to cryobiosis, meaning that tardigrades do not age while frozen.
Tardigrades were subjected to subzero temperature treatment by cooling on agar plates from room temperature down to ‐30°C. The specimens were kept for seven days at ‐30°C without temperature fluctuations, after which the animals were allowed to slowly warm. Live and dead animals were recorded after thawing. Following the thawing period, we started the feeding period, in which the active animals were fed for seven days. At the end of the feeding period, the numbers of live and dead animals were documented and the same subzero temperature treatment imposed again. The weekly change from freezing to feeding period was repeated until all animals were dead.
Many limno-terrestrial tardigrades live in unstable habitats where they experience extreme environmental conditions such as drought, heat and subzero temperatures. Although their stress tolerance is ...often related only to the anhydrobiotic state, tardigrades can also be exposed to great daily temperature fluctuations without dehydration. Survival of subzero temperatures in an active state requires either the ability to tolerate the freezing of body water or mechanisms to decrease the freezing point. Considering freeze tolerance in tardigrades as a general feature, we studied the survival rate of nine tardigrade species originating from polar, temperate and tropical regions by cooling them at rates of 9, 7, 5, 3 and 1 degrees C h(-1) down to -30 degrees C then returning them to room temperature at 10 degrees C h(-1). The resulting moderate survival after fast and slow cooling rates and low survival after intermediate cooling rates may indicate the influence of a physical effect during fast cooling and the possibility that they are able to synthesize cryoprotectants during slow cooling. Differential scanning calorimetry of starved, fed and cold acclimatized individuals showed no intraspecific significant differences in supercooling points and ice formation. Although this might suggest that metabolic and biochemical preparation are non-essential prior to subzero temperature exposure, the increased survival rate with slower cooling rates gives evidence that tardigrades still use some kind of mechanism to protect their cellular structure from freezing injury without influencing the freezing temperature. These results expand our current understanding of freeze tolerance in tardigrades and will lead to a better understanding of their ability to survive subzero temperature conditions.
A
bstract
We consider an axion-like particle (ALP) coupled to Standard Model (SM) fermions as a mediator between the SM and a fermionic dark matter (DM) particle. We explore the case where the ALP-SM ...and/or the ALP-DM couplings are too small to allow for DM generation via standard freeze-out. DM is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (DFO). In the DFO regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled Boltzmann equations, one of which describes the energy transfer from the SM to the dark sector. Having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rare
B
and
K
decays, exotic Higgs decays at the LHC, astrophysics, dark matter searches and cosmology. In particular, for our specific ALP scenario we (re) calculate and improve beam dump, flavour and supernova constraints. Throughout our calculation we implement state-of-the-art chiral perturbation theory results for the ALP partial decay width to hadrons. We find that while the DFO region, which predicts extremely small ALP-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. Some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments.
The microbiome of freshwater sponges is rarely studied, and not a single novel bacterial species has been isolated and subsequently characterized from a freshwater sponge to date. A previous study ...showed that 14.4% of the microbiome from Ephydatia fluviatilis belong to the phylum Planctomycetes. Therefore, we sampled an Ephydatia sponge from a freshwater lake and employed enrichment techniques targeting bacteria from the phylum Planctomycetes. The obtained strain spb1T was subject to genomic and phenomic characterization and found to represent a novel planctomycetal species proposed as Planctopirus ephydatiae sp. nov. (DSM 106606 = CECT 9866). In the process of differentiating spb1T from its next relative Planctopirus limnophila DSM 3776T, we identified and characterized the first phage – Planctopirus phage vB_PlimS_J1 – infecting planctomycetes that was only mentioned anecdotally before. Interestingly, classical chemotaxonomic methods would have failed to distinguish Planctopirus ephydatiae strain spb1T from Planctopirus limnophila DSM 3776T. Our findings demonstrate and underpin the need for whole genome-based taxonomy to detect and differentiate planctomycetal species.
One of the most highly debated questions in the field of animal swarming and social behaviour is the collective random patterns and chaotic behaviour formed by some animal species, in particular if ...there is a danger. Is such a behaviour beneficial or unfavourable for survival? Here we report on one of the most remarkable forms of animal swarming and social behaviour -fish schooling- from a hydrodynamic point of view. We found that some fish species do not have preferred orientation and they swarm in a random pattern mode, despite the excess of energy consumed. Our analyses, which include calculations of the hydrodynamic forces between slender bodies, show that such a behaviour may enhance the transfer of hydrodynamic information, and thus the survivability of the school could improve. These findings support the general hypothesis that a disordered and nontrivial collective behaviour of individuals within a nonlinear dynamical system is essential for optimising transfer of information -an optimisation that might be crucial for survival.
A
bstract
We consider the minimal supersymmetric Standard Model with large scalar and gaugino mass terms at the GUT scale, which are generated predominantly by gauge-mediated supersymmetry breaking. ...For certain ratios of GUT-scale masses, determined by the messenger indices, large radiative corrections lead to a small electroweak scale in a way which resembles the well-known focus point mechanism. The Fermi scale, the gravitino mass and the higgsino masses are of comparable size. For a Higgs mass of about 124 GeV all other superparticles have masses outside the reach of the LHC.
A
bstract
In supersymmetric extensions of the Standard Model, the Fermi scale of electroweak symmetry breaking is determined by the pattern of supersymmetry breaking. We present an example, motivated ...by a higher-dimensional GUT model, where a particular mass relation between the gauginos, third-generation squarks and Higgs fields of the MSSM leads to a Fermi scale smaller than the soft mass scale. This is in agreement with the measured Higgs boson mass. The
μ
parameter is generated independently of supersymmetry breaking, however the
μ
problem becomes less acute due to the little hierarchy between the soft mass scale and the Fermi scale as we will argue. The resulting superparticle mass spectra depend on the localization of quark and lepton fields in higher dimensions. In one case, the squarks of the first two generations as well as the gauginos and higgsinos can be in the range of the LHC. Alternatively, only the higgsinos may be accessible at colliders. The lightest superparticle is the gravitino.
Next-to-minimal dark matter at the LHC Bharucha, A.; Brümmer, F.; Desai, N.
The journal of high energy physics,
11/2018, Volume:
2018, Issue:
11
Journal Article
Peer reviewed
Open access
A
bstract
We examine the collider signatures of a WIMP dark matter scenario comprising a singlet fermion and an SU(2)
n
-plet fermion, with a focus on
n
= 3 and
n
= 5. The singlet and
n
-plet masses ...are of the order of the electroweak scale. The
n
-plet contains new charged particles which will be copiously pair-produced at the LHC. Small mixing angles and near-degenerate masses, both of which feature naturally in these models, give rise to long-lived particles and their characteristic collider signatures. In particular, the
n
= 5 model can be constrained by displaced lepton searches independently of the mixing angle, generically ruling out 5-plet masses below about 280 GeV. For small mixing angles, we show that there is a parameter range for which the model reproduces the observed thermal relic density but is severely constrained by disappearing track searches in both the
n
= 3 and the
n
= 5 cases. The
n
= 3 model is further constrained by soft di-lepton searches irrespective of whether any of the new particles are long-lived.
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