arXiv subjects

Rakhi Mahbubani

Publications and source records attributed to Rakhi Mahbubani.

At least 19 recordsLinked to original sources

arXiv2026

Soft-Dimuon Signature from Two-Component Scalar Dark Matter at the LHC

We explore the potential of the Large Hadron Collider to probe a two-component scalar dark matter scenario in the opposite-sign dimuon plus missing transverse energy final state, accompanied by a hard jet. The signal features a soft dimuon system with an invariant mass well below $m_Z$. We consider a 3-Higgs Doublet Model with one active and two inert scalar doublets, where a $Z_2 \times Z_2'$ symmetry stabilises the lightest neutral scalar in each inert sector, yielding two scalar DM candidates. The relevant parameter space is mapped in terms of the two DM masses and the mass splittings between each DM candidate and its corresponding next-to-lightest scalar state. We perform a detector-level Monte Carlo analysis and design a dedicated cut-based selection, including a transverse-mass requirement adapted to the signal topology. For a representative benchmark, we obtain $S/B\simeq 9.8%$ and a statistical-only significance of $S/\sqrt{B}=1.35$ at Run 3 with ${\cal L}=300~{\rm fb}^{-1}$, increasing to $S/\sqrt{B}=4.93$ under a statistical-only extrapolation to ${\cal L}=4~{\rm ab}^{-1}$. Before the full selection, the two dark sectors generate a double-bump structure in the dimuon invariant-mass distribution. After the cuts optimised for inclusive sensitivity, however, this feature is not statistically robust enough to establish the two-component origin of the signal. The benchmark is underabundant and is interpreted as a subdominant two-component DM scenario, while the collider analysis remains independent of its cosmological abundance. Although the numerical study is carried out in the I(2+1)HDM, the results are applicable to weakly interacting sectors with similar electroweak associated production and cascade decays, where a heavier state separated from the DM candidate by less than $m_Z$ produces a soft muon pair via an off-shell $Z$ boson.

hep-ph↗

arXiv2026

Open LHC Monte Carlo Event Generation

The LHC physics programme involves a vast amount of Monte Carlo event simulation. This paper reviews current efforts towards sharing the generated events as Open Data. Open Event Generation helps reduce duplication of effort and resource consumption, and benefits the whole High Energy Physics community. We give examples of use cases and user experiences, discuss financial and environmental savings, and suggest future directions.

hep-ph↗

arXiv2025

Input to European Strategy Update for Particle Physics: Sustainability

Human activity continues to have an enormous negative impact on the ability of the planet to sustain human and other forms of life. Six out of the nine planetary boundaries have been crossed, a seventh is close to threshold. Prominent manifestations of this development are climate change caused by greenhouse gas emissions, as well as loss of biodiversity. In recognition of the urgency of these problems, several international agreements have been ratified to achieve net-zero emissions and to halt and reverse biodiversity loss. Significant reductions in emissions are required by 2030 to meet international climate targets. The field of particle physics has an obligation and an opportunity to contribute to such mitigation efforts and to avoid causing further harm. This document urges the European Strategy Update in Particle Physics to set a clear and bold mandate for embedding environmental sustainability throughout the future scientific programme, and advocates for a series of actions that will enable this.

physics.soc-ph↗

arXiv2025

Reinterpretation and preservation of data and analyses in HEP

Data from particle physics experiments are unique and are often the result of a very large investment of resources. Given the potential scientific impact of these data, which goes far beyond the immediate priorities of the experimental collaborations that obtain them, it is imperative that the collaborations and the wider particle physics community publish and preserve sufficient information to ensure that this impact can be realised, now and into the future. The information to be published and preserved includes the algorithms, statistical information, simulations and the recorded data. This publication and preservation requires significant resources, and should be a strategic priority with commensurate planning and resource allocation from the earliest stages of future facilities and experiments.

hep-ph↗

arXiv2023

Environmental sustainability in basic research: a perspective from HECAP+

The climate crisis and the degradation of the world's ecosystems require humanity to take immediate action. The international scientific community has a responsibility to limit the negative environmental impacts of basic research. The HECAP+ communities (High Energy Physics, Cosmology, Astroparticle Physics, and Hadron and Nuclear Physics) make use of common and similar experimental infrastructure, such as accelerators and observatories, and rely similarly on the processing of big data. Our communities therefore face similar challenges to improving the sustainability of our research. This document aims to reflect on the environmental impacts of our work practices and research infrastructure, to highlight best practice, to make recommendations for positive changes, and to identify the opportunities and challenges that such changes present for wider aspects of social responsibility.

physics.soc-ph↗

arXiv2023

Optimizing pixel tracklet searches for shorter lifetimes

Pixel tracklets, disappearing tracks reconstructed with only pixel hits, have proven to be a promising technique in LHC analyses to search for dark matter candidates at the LHC that belong to a nearly-degenerate electroweak multiplet. However, a Pseudo-Dirac electroweak doublet fermion, arguably the most interesting such possibility, has a shorter lifetime and therefore existing tracklet searches are less sensitive in this case. We assess the performance of a tracklet search optimized for shorter lifetimes by requiring only three pixel hits for the tracklet reconstruction, and by demanding an accompanying soft track for suppressing backgrounds. We estimate how far the sensitivity of existing searches can be extended into the region of parameter space with this optimized search.

hep-ph↗

arXiv2021

Dark Nucleosynthesis: Cross-sections and Astrophysical Signals

We investigate dark matter bound-state formation and its implication for indirect-detection experiments. We focus on the case where dark matter is a baryon of a strongly-coupled dark sector and provide generic formulae for the formation of shallow nuclear bound states on emission of photons, and W and Z gauge bosons. These processes can occur via electric and magnetic transitions, and give rise to indirect signals that are testable in monochromatic and diffuse photon measurements by Fermi and HESS. We also study the validity of factorizing the bound-state formation cross section into a short-distance nuclear part multiplied by Sommerfeld-enhancement factors. We find that the short-distance nuclear potential often violates factorization, modifying in particular the location of the peaks associated with zero-energy bound states. Finally we revisit bound-state formation of a (weakly-coupled) Minimal DM quintuplet including isospin-breaking effects, and find it gives rise to indirect-detection signals that are compatible with current bounds.

hep-ph↗

arXiv2020

Indirect Detection of Composite (Asymmetric) Dark Matter

Dark Matter can form bound states upon the emission of quanta of energy equal to the binding energy. The rate of this process is large for strongly-interacting Dark Matter, and further enhanced by long distance effects. The resulting monochromatic and diffuse $γ$-rays can be tested in indirect detection experiments. If Dark Matter has electroweak charge, indirect signals include multiple observable photon lines for masses in the TeV range. Else if it couples only via a dark photon portal, diffuse spectra from dwarf galaxies and CMB reionization set powerful limits for masses below a TeV. This mechanism provides a powerful means of probing Asymmetric Dark Matter today.

hep-ph↗

arXiv2020

Boosting the dark matter signal with Coulomb resonances

We show that the presence of nearby Coulombic resonances at finite energy could lead to the enhancement of the dark matter annihilation cross section at specific non-zero velocities correlated with the mass splitting between the dark matter pair and that of the resonance. If one of these resonant velocities approximately matches the velocity of dark matter in our local neighbourhood, we would see this enhancement in existing indirect-detection measurements, such as the measurements of the continuum photon spectrum made by HESS and Fermi-LAT. We explore this effect in the context of pure Higgsino and Wino dark matter with a variable splitting between charged and neutral components, controlled by the Wilson coefficient of a higher-dimension operator. For electroweak WIMPs a relevant and appreciable enhancement from Coulomb resonances requires tuning the charged-neutral splitting to be of order the Coulomb binding energies. This leads to strong exclusions of Higgsino dark matter with charged-neutral splittings in the narrow ranges (2, 2.5) and (8.5, 10.5) MeV. In contrast, by decreasing the charged-neutral splitting for the thermal Wino, we can move the Yukawa resonance away from the thermal relic mass, decreasing the indirect-detection signal to a level that is compatible with HESS measurements in the window (25, 35) MeV.

hep-ph↗

arXiv2018

Probing compressed dark sectors at 100 TeV in the dileptonic mono-Z channel

We examine the sensitivity at a future 100 TeV proton-proton collider to compressed dark sectors whose decay products are invisible due to below-threshold energies and/or small couplings to the Standard Model. This scenario could be relevant to models of WIMP dark matter, where the lightest New Physics state is an (isolated) electroweak multiplet whose lowest component is stable on cosmological timescales. We rely on the additional emission of a hard on-shell $Z$-boson decaying to leptons, a channel with low background systematics, and include a careful estimate of the real and fake backgrounds to this process in our analysis. We show that an integrated luminosity of 30 ab$^{-1}$ would allow exclusion of a TeV-scale compressed dark sector with inclusive production cross section of 0.3 fb, for 1\% background systematic uncertainty and splittings below 5 GeV. This translates to exclusion of a pure higgsino (wino) multiplet with mass of 500 (970) GeV.

hep-ph↗

arXiv2018

Precision Tests and Fine Tuning in Twin Higgs Models

We analyze the parametric structure of Twin Higgs (TH) theories and assess the gain in fine tuning which they enable compared to extensions of the Standard Model with colored top partners. Estimates show that, at least in the simplest realizations of the TH idea, the separation between the mass of new colored particles and the electroweak scale is controlled by the coupling strength of the underlying UV theory, and that a parametric gain is achieved only for strongly-coupled dynamics. Motivated by this consideration we focus on one of these simple realizations, namely composite TH theories, and study how well such constructions can reproduce electroweak precision data. The most important effect of the Twin states is found to be the infrared contribution to the Higgs quartic coupling, while direct corrections to electroweak observables are sub-leading and negligible. We perform a careful fit to the electroweak data including the leading-logarithmic corrections to the Higgs quartic up to three loops. Our analysis shows that agreement with electroweak precision tests can be achieved with only a moderate amount of tuning, in the range 5-10\%, in theories where colored states have mass of order 3-5 TeV and are thus out of reach of the LHC. For these levels of tuning, larger masses are excluded by a perturbativity bound, which makes these theories possibly discoverable, hence falsifiable, only at a future 100 TeV collider.

hep-ph↗

arXiv2017

Closing the window for compressed Dark Sectors with disappearing charged tracks

We investigate the sensitivity at current and future hadron colliders to a heavy electrically-charged particle with a proper decay length below a centimetre, whose decay products are invisible due to below-threshold energies and/or small couplings to the Standard Model. A cosmologically-motivated example of a framework that contains such a particle is the Minimal Supersymmetric Standard Model in the limit of pure Higgsinos. The current hadron-collider search strategy has no sensitivity to the upper range of pure Higgsino masses that are consistent with the thermal relic density, even at a future collider with 100 TeV centre-of-mass energy. We show that performing a disappearing track search within the inner 10 cm of detector volume would improve the reach in lifetime by a factor of 3 at the 14 TeV LHC and a further factor of 5 at a 100 TeV collider, resulting in around 10 events for 1.1 TeV thermal Higgsinos. In order to include the particles with the largest boost in the analysis, we furthermore propose a purely track-based search in both the central and forward regions, each of which would increase the number of events by another factor of 5, improving our reach at small lifetimes. This would allow us to definitively discover or exclude the experimentally-elusive pure-Higgsino thermal relic at a 100 TeV collider.

hep-ph↗

arXiv2015

Probing top-antitop resonances with $t\bar{t}$ scattering at LHC14

We explore the sensitivity of the LHC at 14 TeV centre-of-mass energy (LHC14) to the single production and decay of top-antitop resonances in the four-top final state. We focus on the same-sign dilepton channel, and work within a simplified model with a vector boson coupling to the Standard Model only via its interactions with right-handed top quarks. We find it is possible to discover (exclude) such a vector boson with 300 fb$^{-1}$ of integrated luminosity up to a mass of 1.2 (1.6) TeV for a modest coupling to tops of $g_ρ$=2. We present our results as an exclusion limit on the cross-section$\times$branching ratio for ease of recasting, and interpret them in the context of the gauge-singlet vector boson $ρ_X$ present in many simple Composite Higgs theories.

hep-ph↗

arXiv2014

The Gran Sasso muon puzzle

We carry out a time-series analysis of the combined data from three experiments measuring the cosmic muon flux at the Gran Sasso laboratory, at a depth of 3800 m.w.e. These data, taken by the MACRO, LVD and Borexino experiments, span a period of over 20 years, and correspond to muons with a threshold energy, at sea level, of around 1.3 TeV. We compare the best-fit period and phase of the full muon data set with the combined DAMA/NaI and DAMA/LIBRA data, which spans the same time period, as a test of the hypothesis that the cosmic ray muon flux is responsible for the annual modulation detected by DAMA. We find in the muon data a large-amplitude fluctuation with a period of around one year, and a phase that is incompatible with that of the DAMA modulation at 5.2 sigmas. Aside from this annual variation, the muon data also contains a further significant modulation with a period between 10 and 11 years and a power well above the 99.9% C.L threshold for noise, whose phase corresponds well with the solar cycle: a surprising observation for such high energy muons. We see no corresponding long-period oscillation in the stratospheric temperature data.

astro-ph.HE↗

arXiv2012

Light non-degenerate squarks at the LHC

Experimental bounds on squarks of the first two generations assume their masses to be eightfold degenerate, and consequently constrain them to be heavier than ~ 1.4 TeV when the gluino is lighter than 2.5 TeV. The assumption of squark-mass universality is neither a direct consequence of Minimal Flavor Violation (MFV), which allows for splittings within squark generations, nor a prediction of supersymmetric alignment models, which allow for splittings between generations. We reinterpret a recent CMS multijet plus missing energy search allowing for deviations from U(2) universality, and show that the squark bounds are significantly weakened: a 400 GeV second-generation squark singlet is allowed, even with exclusive decays to a massless neutralino; and in an MFV scenario, the down-type squark singlets can be as light as 600 GeV provided the up-type singlets are pushed up to 1.8 TeV, for a 1.5 TeV gluino and decoupled doublet squarks.

hep-ph↗

arXiv2012

Re-interpreting the Oxbridge stransverse mass variable MT2 in general cases

We extend the range of possible applications of MT2 type analyses to decay chains with multiple invisible particles, as well as to asymmetric event topologies with different parent and/or different children particles. We advocate two possible approaches. In the first, we introduce suitably defined 3+1-dimensional analogues of the MT2 variable, which take into account all relevant on-shell kinematic constraints in a given event topology. The second approach utilizes the conventional MT2 variable, but its kinematic endpoint is suitably reinterpreted on a case by case basis, depending on the specific event topology at hand. We provide the general prescription for this reinterpretation, including the formulas relating the measured MT2 endpoint (as a function of the test masses of all the invisible particles) to the underlying physical mass spectrum. We also provide analytical formulas for the shape of the differential distribution of the doubly projected MT2(perp) variable for the ten possible event topologies with one visible particle and up to two invisible particles per decay chain. We illustrate our results with the example of leptonic chargino decays, (chargino to lepton, neutrino and LSP) in supersymmetry.

hep-ph↗

arXiv2011

Counting dark matter particles in LHC events

We suggest trying to count the number of invisible particles produced in missing energy events at the LHC, arguing that multiple production of such particles provides evidence that they constitute stable Dark Matter and that counting them could yield further insights into the nature of Dark Matter. We propose a method to count invisible particles, based on fitting the shapes of certain transverse- or invariant-mass distributions, discuss various effects that may affect the measurement, and simulate the use of the method to count neutrinos in Standard Model processes and Dark Matter candidates in new physics processes.

hep-ph↗

arXiv2009

Inflation on the Brane with Vanishing Gravity

Many existing models of brane inflation suffer from a steep irreducible gravitational potential between the branes that causes inflation to end too early. Inspired by the fact that point masses in 2+1 D exert no gravitational force, we propose a novel unwarped and non-supersymmetric setup for inflation, consisting of 3-branes in two extra dimensions compactified on a sphere. The size of the sphere is stabilized by a combination of a bulk cosmological constant and a magnetic flux. Computing the 4D effective potential between probe branes in this background, we find a non-zero contribution only from exchange of level-1 KK modes of the graviton and radion. Identifying antipodal points on the 2-sphere projects out these modes, eliminating entirely the troublesome gravitational contribution to the inflationary potential.

hep-th↗