arXiv subjects

Alexander Belyaev

Publications and source records attributed to Alexander Belyaev.

At least 37 records · Page 2Linked to original sources

arXiv2022

Single Vector-Like top quark production via chromomagnetic interactions at present and future hadron colliders $-$A Snowmass 2021 White Paper

In our recent paper, we have investigated the potential for the LHC to discover vector-like quark partner states singly produced via their chromomagnetic moment interactions. These production mechanisms extend traditional searches which rely on pair-production of top-quark partner states or on the single production of these states through electroweak interactions, in the sense of providing greatly increased reach in parameter space regions where traditional searches are insensitive. In this study we determine the potential of both the 14 TeV high-luminosity LHC (HL-LHC) and a 100 TeV proton-proton collider to probe new vector-like quarks produced in this mode. We focus on the single production of a top-quark partner in association with an ordinary top-quark, as well as on the resonant production of the bottom-quark partner with its subsequent decay to a top-quark partner and a $W$ boson. For both cases we consider a top-partner decay to the Higgs boson and an ordinary top-quark. We find that HL-LHC and a future 100 TeV proton collider can probe vector-like partner masses up to about 3 TeV and 15-20 TeV respectively, visibly extending the range of the traditional vector like quark partner searches.

hep-ph↗

arXiv2022

Decoding Dark Matter at future $e^+ e^-$ colliders

We explore the potential of the $e^+ e^-$ colliders to discover dark matter and determine its properties such as mass and the spin. For this purpose we study spin zero and spin one-half cases of dark matter, $D$ which belongs to $SU(2)$ weak doublet and therefore has the charged doublet partner, $D^+$. For the case of scalar dark matter we chose Inert Doublet Model, while for the case of fermion dark matter we suggest the new minimal fermion dark matter model with only three parameters. We choose two benchmarks for the models under study which provide the correct amount of observed DM relic density and consistent with the current DM searches. We focus on the particular process $e^+ e^- \to D^+ D^- \to D D W^+ W^- \to DD(q \bar{q})(μ^\pmν)$ at 500 GeV ILC collider which gives rise to the "di-jet +$μ$ + missing $E_T$" signature and study it at the level of fast detector simulation, taking into account Bremsstrahlung and ISR effects. We have found that two kinematical observables -- the energy of the muon, $E_μ$, and the angular distribution of $W$-boson, reconstructed from di-jet, $\cosθ_{jj}$ are very powerful in determination of DM mass and spin, respectively. In particular we have demonstrated that in case of fermion DM, the masses can be measured with a few percent accuracy already at 500 fb$^{-1}$ integrated luminosity. At the same time, the scalar DM model which has about an order of magnitude lower signal, requires about factor of 40 higher luminosity to reach the same accuracy in the mass measurement. We have found that one can distinguish fermion and scalar DM scenarios with about 2 ab$^{-1}$ total integrated luminosity or less without using the information on the cross sections for benchmarks under study.

hep-ph↗

arXiv2022

Multilepton Signatures from Dark Matter at the LHC

Leptonic signatures of Dark Matter (DM) are one of the cleanest ways to discover such a secluded form of matter at high energy colliders. We explore the full parameter space relevant to multi-lepton (2- and 3-lepton) signatures at the Large Hadron Collider (LHC) from representative minimal consistent models with scalar and fermion DM. In our analysis, we suggest a new parametrisation of the model parameter spaces in terms of the DM mass and mass differences between DM and its multiplet partners. This parametrisation allows us to explore properties of DM models in their whole parameter space. This approach is generic and quite model-independent since the mass differences are related to the couplings of the DM to the Standard Model (SM) sector. We establish the most up-to-date LHC limits on the inert 2-Higgs Doublet Model (i2HDM) and Minimal Fermion DM (MFDM) model parameter spaces, by using the complementary information stemming from 2- and 3-lepton signatures. We provide a map of LHC efficiencies and cross-section limits for such 2- and 3-lepton signatures allowing one to easily make model-independent reinterpretations of LHC results for analogous classes of models. We also present combined constraints from the LHC, DM relic density and direct search experiments indicating the current status of the i2HDM and MFDM model.

hep-ph↗

arXiv2022

Minimal Consistent Dark Matter models for systematic experimental characterisation: Fermion Dark Matter

The search for a Dark Matter particle is the new grail and hard-sought nirvana of the particle physics community. From the theoretical side, it is the main challenge to provide a consistent and model-independent tool for comparing the bounds and reach of the diverse experiments. We propose a first complete classification of minimal consistent Dark Matter models, which provides the missing link between experiments and top-down models. Consistency is achieved by imposing renormalisability and invariance under the full Standard Model symmetries. We apply this paradigm to fermionic Dark multiplets with up to one mediator. We also reconsider the one-loop contributions to direct detection, including the relevant effect of (small) mass splits in the Dark multiplet. Our work highlights the presence of unexplored viable models, and paves the way for the ultimate systematic hunt for the Dark Matter particle.

hep-ph↗

arXiv2022

Composable and Modular Code Generation in MLIR: A Structured and Retargetable Approach to Tensor Compiler Construction

Despite significant investment in software infrastructure, machine learning systems, runtimes and compilers do not compose properly. We propose a new design aiming at providing unprecedented degrees of modularity, composability and genericity. This paper discusses a structured approach to the construction of domain-specific code generators for tensor compilers, with the stated goal of improving the productivity of both compiler engineers and end-users. The approach leverages the natural structure of tensor algebra. It has been the main driver for the design of progressive lowering paths in \MLIR. The proposed abstractions and transformations span data structures and control flow with both functional (SSA form) and imperative (side-effecting) semantics. We discuss the implications of this infrastructure on compiler construction and present preliminary experimental results.

cs.PL↗

arXiv2022

Minimal Consistent models for systematic Dark Matter exploration

Dark Matter searches in collider and non-collider experiments requires systematic and consistent approach. We suggest and perform classification of Minimal Consistent Dark Matter models which are aimed to create a solid framework for Dark Matter exploration.

hep-ph↗

arXiv2020

Probing Dark Matter with Disappearing Tracks at the LHC

Models where dark matter is a part of an electroweak multiplet feature charged particles with macroscopic lifetimes due to the charged-neutral mass split of the order of pion mass. At the Large Hadron Collider, the ATLAS and CMS experiments will identify these charged particles as disappearing tracks, since they decay into a massive invisible dark matter candidate and a very soft charged Standard-Model particle which fails to pass the reconstruction requirements. While ATLAS and CMS have focused on the supersymmetric versions of these scenarios, we have performed here the reinterpretation of the latest ATLAS disappearing track search for a suite of dark matter multiplets with different spins and electroweak quantum numbers. More concretely, we consider the cases of the inert Two Higgs Doublet model (i2HDM), of Minimal Fermion Dark Matter (MFDM) and of Vector Triplet Dark Matter (VTDM). Our procedure is validated by using the same wino and higgsino benchmark models employed by the ATLAS collaboration. We have found that with the disappearing track signature one can probe a vast portion of the parameter space, well beyond the reach of prompt missing energy searches (notably mono-jets). We provide tables with the upper-limits on the cross-section upper limits, and efficiencies in the lifetime - dark matter mass plane for all the models under consideration. Moreover we make the recasting code employed here publicly available, as part of the LLP Recasting Repository.

hep-ph↗

arXiv2020

Minimal Spin-one Isotriplet Dark Matter

In this work we present a simple extension of the Standard Model that contains, as the only new physics component, a massive spin-one matter field in the adjoint representation of $SU(2)_{L}$. In order to be consistent with perturbative unitarity, the vector field must be odd under a $Z_{2}$ symmetry. Radiative corrections make the neutral component of the triplet ($V^{0}$) slightly lighter than the charged ones. We show that $V^{0}$ can be the dark matter particle while satisfying all current bounds if it has a mass between $2.8$ and $3.8$ TeV. We present the current limit on the model parameter space from highly complementary experimental constraints including dark matter relic density measurement, dark matter direct and indirect detection searches, LHC data on Higgs couplings to photons and LHC data on disappearing track searches. We show that the two-dimensional parameter space can be substantially covered by disappearing track searches at a future 100 TeV hadron collider, which will probe DM mass upto about 1.2 TeV.

hep-ph↗

arXiv2020

Anatomy of the Inert Two Higgs Doublet Model in the light of the LHC and non-LHC Dark Matter Searches

The inert Two Higgs Doublet Model (i2HDM) is a theoretically well-motivated example of a minimal consistent Dark Matter(DM) model which provides mono-jet, mono-Z, mono-Higgs and Vector-Boson-Fusion+Missing Transverse Momentum signatures at the LHC, complemented by signals in direct and indirect DM search experiments. In this paper we have performed a detailed analysis of the constraints in the full 5D parameter space of the i2HDM, coming from perturbativity, unitarity, electroweak precision data, Higgs data from LHC, DM relic density, direct/indirect DM detection and LHC mono-jet analysis, as well as implications of experimental LHC studies on disappearing charged tracks relevant to high DM mass region. We demonstrate the complementarity of the above constraints and present projections for future LHC data and direct DM detection experiments to probe further i2HDM parameter space. The model is implemented into the CalcHEP and micrOMEGAs packages, which are publicly available at the HEPMDB database, and is ready for a further exploration in the context of the LHC, relic density and DM direct detection.

hep-ph↗

arXiv2019

Any Room Left for Technicolor? Holographic Studies of NJL Assisted Technicolour

We use a holographic description of technicolor dynamics to study gauge theories that only break chiral symmetry when aided by a strong four fermion interaction. These Nambu-Jona-Lasinio (NJL) assisted technicolor models provide examples of different dynamics from walking technicolor which can, by tuning, generate a light higgs like $σ$ meson. We compute the vector meson ($ρ$) and axial vector meson (A) spectrum for a variety of models with techni-quarks in the fundamental representation, enlarging the available parameter space over a previous analysis of walking theories. These predictions determine the parameter space of a low energy effective description where LHC constraints from dilepton channels have already been applied. Many of the models with low numbers of electroweak doublets still lie beyond current constraints and motivate exploration of new signatures beyond dilepton for LHC and a 100 TeV proton collider.

hep-ph↗

arXiv2018

Any Room Left for Technicolor? Dilepton Searches at the LHC and Beyond

Precision electroweak data, a light higgs and LHC searches for new spin one particles are all very constraining on technicolor models. We use a holographic model of walking techicolor (WTC) gauge dynamics, tuned to produce a light higgs and low $S$ parameter, to estimate the range of possible vector($ρ$) and pseudo-vector($A$) resonance masses and couplings as a function of the number of colours and the number of flavours of techni-singlet and techni-doublet quarks. The resulting models predict techni-hadron masses and couplings above the current limits from dilepton resonance searches at the LHC because their masses are enhanced by the strong coupling extending into the multi-TeV range, while couplings to Standard Model fermions are partly suppressed. The models emphasize the contortions needed to continue to realize technicolor, {the need to explore new signatures beyond dilepton for LHC and also motivate a 100 TeV proton collider.

hep-ph↗

arXiv2018

Problems with Higgsplosion

A recent calculation of the multi-Higgs boson production in scalar theories with spontaneous symmetry breaking has demonstrated the fast growth of the cross section with the Higgs multiplicity at sufficiently large energies, called "Higgsplosion". It was argued that "Higgsplosion" solves the Higgs hierarchy and fine-tuning problems. In our paper we argue that: a) the formula for "Higgsplosion" has a limited applicability and inconsistent with unitarity of the Standard Model; b) that the contribution from "Higgsplosion" to the imaginary part of the Higgs boson propagator cannot be re-summed in order to furnish a solution of the Higgs hierarchy and fine-tuning problems.

hep-ph↗

arXiv2018

On the initial approximation of charged particle tracks in detectors with linear sensing elements

The search for charged particle tracks in detectors with linear sensing elements, such as wire chambers, strip silicon detectors etc., starts with identification of straight track segments. The latter are deduced by constructing all possible combinations of activated detector elements. In the high multiplicity environment, with many activated detector elements, this causes large combinatorics and significantly reduces the performance of the track finding algorithms. In this report we trace this problem back to determination of the parameters of a straight line build from a number of skew lines (sensing elements of a detector) in space. Based on the intersection points of two hyperbolas, we demonstrate an analytic solution in the case of four skew detector elements.The procedure can also be applied as a first approximation to the more general case of curved track finding.

physics.ins-det↗

arXiv2018

Interplay of the LHC and non-LHC Dark Matter searches in the Effective Field Theory approach

We present accurate and up-to-date constraints on the complete set of dimension five and six operators with scalar, fermion and vector Dark Matter (DM). We find limits using LHC mono-jet data, spin inde- pendent and spin dependent direct searches, relic density and CMB, and show the interplay between high and low energy data in setting bounds on the parameter space. In order to properly compare data taken at different energies, we take into account the effect of the running and mixing of operators. We also take into account the local density uncertainties affecting direct detection data, and apply EFT validity criteria related to the cut on the invariant mass of DM pair production at the LHC, which turns out to be especially important for the case of vector DM. Finally, we estimate the potential of the future LHC runs to probe DM parameter space.

hep-ph↗

arXiv2018

Walking Technicolor in the light of $Z^{\prime}$ searches at the LHC

We investigate the potential of the Large Hadron Collider (LHC) to probe one of the most compelling Beyond the Standard Model (BSM) frameworks --- Walking Technicolor (WTC), involving strong dynamics and having a slowly running (walking) new strong coupling. For this purpose we use recent LHC Run2 data to explore the full parameter space of the minimal WTC model using dilepton signatures from heavy neutral $Z^{\prime}$ and $Z^{\prime\prime}$ resonances predicted by the model. This signature is the most promising one for discovery of WTC at the LHC for the low-intermediate values of the $\tilde g$ coupling -- one of the principle parameters of WTC. We have demonstrated complementarity of the dilepton signals from both resonances, have established the most up-to-date limit on the WTC parameter space, and provided projections for the the LHC potential to probe the WTC parameter space at higher future luminosities and upgraded energy. We have explored the whole four-dimensional parameter space of the model and have found the most conservative limit on the WTC scale $M_A$ above 3 TeV for the low values of $\tilde g$ which is significantly higher than previous limits established by the LHC collaborations.

hep-ph↗

arXiv2017

Di-boson signatures as Standard Candles for Partial Compositeness

Composite Higgs Models are often constructed including fermionic top partners with a mass around the TeV scale, with the top partners playing the role of stabilizing the Higgs potential and enforcing partial compositeness for the top quark. A class of models of this kind can be formulated in terms of fermionic strongly coupled gauge theories. A common feature they all share is the presence of specific additional scalar resonances, namely two neutral singlets and a colored octet, described by a simple effective Lagrangian. We study the phenomenology of these scalars, both in a model independent and model dependent way, including the bounds from all the available searches in the relevant channels with di-boson and di-top final states. We develop a generic framework which can be used to constrain any model containing pseudo-scalar singlets or octets. Using it, we find that such signatures provide strong bounds on the compositeness scale complementary to the traditional EWPT and Higgs couplings deviations. In many cases a relatively light scalar can be on the verge of discovery as a first sign of new physics.

hep-ph↗

arXiv2017

Dark Matter characterization at the LHC in the Effective Field Theory approach

We have studied the complete set of dimension 5 and dimension 6 effective operators involving the interaction of scalar, fermion and vector Dark Matter (DM) with SM quarks and gluons, to explore the possibility to distinguish these operators and characterise the spin of DM at the LHC. We have found that three factors - the effective dimension of the operator, the structure of the SM part of the operator and the parton densities of the SM particles connected to the operator - uniquely define the shape of the (unobservable) invariant mass distribution of the DM pair and, consequently, the shape of the (observable) MET distribution related to it. Using $χ^2$ analysis, we found that at the LHC, with a luminosity of 300 fb$^{-1}$, certain classes of EFT operators can be distinguished from each other. Hence, since DM spin is partly correlated with the factors defining the shape of MET, the LHC can potentially shed a light also on DM spin. We have also observed a drastic difference in the efficiencies (up to two orders of magnitude) for large MET cuts scenarios with different DM spin, thus indicating that the DM discovery potential strongly depends on it. The study we perform here can be applied more generally than within the EFT paradigm, where the DM mediator is not produced on-the-mass-shell, such as the case of t-channel mediator or mediator with mass below $2M_{DM}$, where the invariant mass of the DM pair is not fixed.

hep-ph↗

arXiv2016

Singlets in Composite Higgs Models in light of the LHC di-photon searches

Models of compositeness can successfully address the origin of the Higgs boson, as a pseudo Nambu Goldstone boson (pNGB) of a spontaneously broken global symmetry, and flavour physics via the partial compositeness mechanism. If the dynamics is generated by a confining gauge group with fermionic matter content, there exists only a finite set of models that have the correct properties to account for the Higgs and top partners at the same time. In this letter we explore the theory space of this class of models: remarkably, all of them contain - beyond the pNGB Higgs - a pNGB singlet, $a$, which couples to Standard Model gauge bosons via Wess-Zumino-Witten interactions, thus providing naturally a resonance in di-boson at the LHC. With the assumption that the recently reported di-photon excess at 750 GeV at the LHC arises from the a-resonance, we propose a generic approach on how to delineate the best candidate for composite Higgs models with top-partners. We find that constraints from other di-boson searches severely reduce the theory space of the models under consideration. For the models which can explain the di-photon excess, we make precise and testable predictions for the width and other di-boson resonance searches.

hep-ph↗