arXiv subjects

Rashmish K. Mishra

Publications and source records attributed to Rashmish K. Mishra.

At least 19 recordsLinked to original sources

arXiv2026

EFT Approaches to Sommerfeld Enhancement and Bound States in Singular Potentials

The Sommerfeld enhancement (SE) from long-range interactions, and the related bound state formation rate, can be important non-perturbative inputs to dark matter (DM) annihilation signals. In the presence of singular interaction potentials, the conventional boundary conditions of the Schrödinger equation fail, obfuscating the computation of SE, its physical origin, and its relation to bound states in such potentials. In this work, we clarify the origin of SE in singular potentials in a two-fold manner: using the framework of velocity power counting in non-relativistic effective field theory (NREFT), and via position-space regularization of singular potentials at short distances to compute SE and bound states. We illustrate our findings through the case of pseudoscalar mediators interacting with massive Dirac DM. We find that when such a system arises from a UV-complete theory at weak coupling, no SE is generated. However, in the case of a derivatively coupled pseudoscalar, where the interaction is described by a higher-dimension operator in an effective theory, SE (and bound states) can occur for weak couplings if there is a large hierarchy between the cutoff scale of the effective theory and the dark matter mass. This SE is sensitive to the choice of the UV completion of the potential at short distances, but a non-negligible SE can persist even when the UV physics alone would not generate any SE; we elucidate the interplay of UV and IR physics in this case.

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arXiv2026

Confinement in Holographic Theories at Finite Theta

A strongly coupled confining gauge theory with a non-zero vacuum angle undergoing a deconfinement to confinement phase transition is studied in the holographic gravitational description. A simplified five-dimensional setup is constructed where a bulk scalar models the effect of the vacuum angle, and the suitable boundary conditions on the ultra-violet (UV) and the infra-red (IR) boundaries are identified. The IR boundary condition is motivated by higher dimensional examples where the bulk scalar comes from a Wilson loop on a shrinking cycle. In this five-dimensional dual geometry, and in the limit of small backreaction in the infra-red, the critical temperature for the phase transition is shown to reduce quadratically with the vacuum angle, matching lattice results. The topological susceptibility has a sharp reduction across the critical temperature, also matching lattice results. The rate for the phase transition is estimated as a function of the vacuum angle, and is seen to be enhanced (reduced) when the field theory has a relevant (irrelevant) deformation at high energies. Crucially, for the irrelevant case, the confined phase can get destabilized for a range of parameters. In the context of early universe dynamics, if the vacuum angle is time-dependent, the transition history changes strongly: the deconfined phase can last till much lower temperatures than naively expected, and one can trigger a transition to the confined phase by a change in the vacuum angle, thus providing a controlled way to generate supercooling. As a phenomenological application, the peak frequency and the power of resulting gravitational wave signal from bubble collisions change, affecting their visibility in detectors. Possible generalizations of the scenario are discussed.

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arXiv2026

Inflation with a Growing Fifth Dimension

Inflation generally assumes a field with nonzero potential that leads to inflationary expansion happening at arbitrarily early times. We demonstrate potentially observable consequences of inflation with a finite initial time in a model in five-dimensional warped anti-de Sitter space, with both a UV and an IR brane present during inflation. Considering an inflaton with an approximately flat potential localized on the UV brane, we derive the resulting brane motion in the bulk and the 4D effective action describing the dynamics. A concrete model allows us to evaluate possible consequences of a starting point of inflation. The background evolution is driven by the fast roll of the radion at early times and the slow roll of the inflaton at late times. We find that the action has the form of a two-field hyperbolic inflation model, the two fields being the radion and the inflaton, both of which have a time-dependent background solution. This setup is holographically dual to an inflaton coupled to a strongly coupled confining sector in which the ratio of the confinement scale to the 4D Planck scale evolves cosmologically. Focusing on the period when the equation of state becomes that of inflation, we find that the presence of the IR brane leads to deviations from the approximate de Sitter background in addition to those from the slow-roll parameters of the inflaton potential. We quantify the effect of the presence of the IR brane on the two point function of the adiabatic scalar perturbations and tensor perturbations. The dominant deviations occur at large scales: the adiabatic power spectrum has a blue tilt, while the tensor power spectrum shows oscillatory features. We present numerical fits to the shape of the adiabatic power spectrum, and discuss the implications for cosmic microwave background (CMB) analysis.

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arXiv2025

Phase Transition to RS: Cool, not Supercool

Motivated by the warped conifold compactification, we model the infrared (IR) dynamics of confining gauge theories in a Randall-Sundrum (RS)-like setup by modifying the stabilizing Goldberger-Wise (GW) potential so that it becomes large (in magnitude) in the IR and back-reacts on the geometry. We study the high-temperature phase by considering a black brane background in which we calculate the entropy and free energy of the strongly back-reacted solution. As with Buchel's result for the conifold (arXiv:2103.15188), we find a minimum temperature beyond which the black brane phase is thermodynamically unstable. In the context of a phase transition to the confining background, our results suggest that the amount of supercooling that the metastable black brane phase undergoes can be limited. It also suggests the first-order phase transition (and the associated gravitational waves from bubble collision) is not universal. Our results therefore have important phenomenological implications for early universe model building in these scenarios.

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arXiv2025

Density of States, Black Holes and the Emergent String Conjecture

We study universal features of the density of one-particle states $ρ(E)$ in weakly coupled theories of gravity at energies above the quantum gravity cutoff $Λ$, defined as the scale suppressing higher-derivative corrections to the Einstein--Hilbert action. Using thermodynamic properties of black holes, we show that in asymptotically flat spacetimes, certain features of $ρ(E)$ above the black hole threshold $M_{\rm min}$ are an indicator for the existence of large extra dimensions, and cannot be reproduced by any lower-dimensional field theory with finitely many fields satisfying the weak energy condition. Based on the properties of gravitational scattering amplitudes, we argue that there needs to exist a (possibly higher-dimensional) effective description of gravity valid up to the cutoff $Λ$. Combining this with thermodynamic arguments we demonstrate that $ρ(E)$ has to grow exponentially for energies $Λ\ll E \ll M_{\rm min}$. Furthermore we show that the tension of any weakly coupled $p$-brane with $p\geq 1$ is bounded from below by $Λ^{p+1}$. We use this to argue that any tower of weakly coupled states with mass below $Λ$ has to be a Kaluza--Klein (KK) tower. Altogether these results indicate that in gravitational weak-coupling limits the lightest tower of states is either a KK tower, or has an exponentially growing degeneracy thereby resembling a string tower. This provides evidence for the Emergent String Conjecture without explicitly relying on string theory or supersymmetry.

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arXiv2024

Evaporating Axion Dark Matter and the Hubble Constant

Axion-like particles are a well-motivated dark matter candidate that can form a condensate with low momentum and high occupation number. In the presence of dark radiation, this condensate loses energy, naturally increasing the energy density of the universe around matter-radiation equality without requiring additional inputs. This general mechanism may offer a solution to the Hubble tension.

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arXiv2023

Consequences of a Stabilizing Field's Self-Interactions for RS Cosmology

It has been argued that the Randall-Sundrum (RS) phase transition rate is suppressed when the holographic theory corresponds to a large $N$ Yang-Mills and when the stabilizing field has a small mass. Here we argue that self-interactions can alleviate the latter suppression. We consider a cubic term in the bulk potential for the Goldberger-Wise (GW) scalar that is responsible for stabilizing the RS geometry. Adding a cubic term suffices to separate the two roles of the GW stabilization: generating a large hierarchy and triggering confinement. We study the resulting radion potential and the dynamics of the early universe phase transition. For a negative coefficient of the cubic term, the effect of the cubic becomes important in the infra-red, and the resulting radion potential is deeper, thereby increasing the radion mass while maintaining a large hierarchy. Staying within the radion effective field theory, we calculate the rate of bubble nucleation from the hot phase to the confined RS phase, both in thin and thick wall limits. The cubic term enhances the rate and allows relaxing the condition on the maximum number of colors $N_\text{max}$ of the dual theory for which the phase transition can be completed. Importantly, this reduces the amount of supercooling that the false vacuum undergoes, increases the peak frequency of the gravitational waves (GW) produced from bubble collisions, and reduces the strength of the GW signal. The reduced GW signal is however still within the reach of proposed space-based GW detectors.

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arXiv2022

Model Agnostic Probes of Dark Sectors at Neutrino Experiments

Present and upcoming neutrino experiments can have considerable sensitivity to dark sectors that interact feebly with the Standard Model. We consider dark sectors interacting with the SM through irrelevant portals that are motivated on general principles. We derive bounds on such scenarios by considering decays of dark sector excitations inside the neutrino detector, placed downstream from the target. Our approach is model agnostic and applies to a wide range of dark sector models, both strongly and weakly coupled. In this approach, the dark sector is characterized by two scales: $Λ_\text{UV}$ (mass of mediators generating the portals) and $Λ_\text{IR}$ (mass gap of the dark sector). At intermediate energies, far away from these scales, the theory is approximately scale-invariant. This allows the calculation of production rates independent of the threshold corrections, although some mild model-dependent assumptions are needed. We look at various dark sector production processes relevant at neutrino experiments such as meson decays, direct partonic production, and dark bremsstrahlung. We consider representative experiments from past (CHARM), present (ICARUS, NOvA, MicroBooNE), and upcoming future (DUNE-MPD), and compare their reach to existing bounds from high energy experiments (LHC and LEP) and dedicated future LLP experiments (SHiP). We find that the upcoming DUNE-MPD can probe $Λ_\text{UV}$ in the TeV range, and $Λ_\text{IR}$ in the 0.1-1 GeV range, covering parts of parameter space currently inaccessible in high energy experiments and fixed-target/beam-dump experiments, and is comparable to future LLP experiments. In general, future neutrino experiments can be an efficient probe of dark sectors, providing complementary as well as new reach in parameter space.

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arXiv2022

TF08 Snowmass Report: BSM Model Building

We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas.

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arXiv2022

Confinement in de Sitter Space and the Swampland

The relation between confinement scale $Λ_c$ of a gauge theory and the Hubble scale $H$ of the background quasi de Sitter space, required to satisfy the Festina Lente criteria ($Λ_c \gtrsim H$) from swampland principles, are investigated for a holographic theory using the Karch-Randall setup. A purely gravitational description admits unstable de Sitter extremum, and the requirement of Festina Lente translates into requirements of a perturbative gravitational dual, but prohibits an arbitrarily small hierarchy for other parameters fixed. With an additional scalar sector, the theory admits metastable de Sitter minima, and the requirement of Festina Lente imposes constraints on the parameters. For some range of parameters where Festina Lente could be constraining, the de Sitter minimum is very close to decay, thus invalidating the applicability. Further consequences of the finite lifetime of the dS extrema and the relation with related swampland conjectures are investigated, and no contradictions are found. These results make case for the consistency and utility of the Karch-Randall setup, clarify the implications of Festina Lente for holographic theories, and connect Festina Lente to other swampland conjectures.

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arXiv2022

Snowmass2021 White Paper: Collider Physics Opportunities of Extended Warped Extra-Dimensional Models

While the warped extra-dimensional models provide an attractive solution to both the gauge and the flavor hierarchy problems, the mass scale of new particles predicted by the minimal models would be beyond the reach of the LHC. Models of extended warped extra dimensions have been proposed to evade these issues and their collider implications have been investigated for the last decade. This white paper summarizes the recent developments in the context of collider phenomenology. The strategies and lessons are broad, and provide a template to extend the experimental program, to cover a wider class of signals in other new physics scenarios as well.

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arXiv2022

Warped Compactifications in Particle Physics, Cosmology and Quantum Gravity

Particle physics has evolved in the past decade through evaluating the consequences of experimental measurements as well as exploiting theoretical tools that permit exploration of new model building and cosmological possibilities. Particularly due to insights from the AdS/CFT correspondence, higher-dimensional warped compactifications, in particular, have played a big role in recent developments by allowing a study of regimes of parameters that would otherwise be intractable. Similarly, theoretical developments in quantum gravity benefit from the bigger range of possibilities that can be explored using warped geometry, allowing for constructions of string vacua with positive cosmological constant and for the exploration of entanglement and information transfer in arbitrary dimensions. Puzzles remain in both more phenomenologically oriented and more theoretically oriented contexts which form the basis for a rich research program in the future as well.

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arXiv2022

Probing New Gauge Forces with a High-Energy Muon Beam Dump

We propose a new beam dump experiment at a future TeV-scale muon collider. A beam dump would be an economical and effective way to increase the discovery potential of the collider complex in a complementary regime. In this work we consider vector models such as the dark photon and $L_μ-L_τ$ gauge boson as new physics candidates and explore which novel regions of parameter space can be probed with a muon beam dump. We find that for the dark photon model, we gain sensitivity in the moderate mass (MeV - GeV) range at both higher and lower couplings compared to existing and proposed experiments, and gain access to previously untouched areas of parameter space of the $L_μ-L_τ$ model.

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arXiv2021

Challenges for Unsupervised Anomaly Detection in Particle Physics

Anomaly detection relies on designing a score to determine whether a particular event is uncharacteristic of a given background distribution. One way to define a score is to use autoencoders, which rely on the ability to reconstruct certain types of data (background) but not others (signals). In this paper, we study some challenges associated with variational autoencoders, such as the dependence on hyperparameters and the metric used, in the context of anomalous signal (top and $W$) jets in a QCD background. We find that the hyperparameter choices strongly affect the network performance and that the optimal parameters for one signal are non-optimal for another. In exploring the networks, we uncover a connection between the latent space of a variational autoencoder trained using mean-squared-error and the optimal transport distances within the dataset. We then show that optimal transport distances to representative events in the background dataset can be used directly for anomaly detection, with performance comparable to the autoencoders. Whether using autoencoders or optimal transport distances for anomaly detection, we find that the choices that best represent the background are not necessarily best for signal identification. These challenges with unsupervised anomaly detection bolster the case for additional exploration of semi-supervised or alternative approaches.

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arXiv2021

Holographic BCFTs and Communicating Black Holes

We study the AdS/BCFT duality between two-dimensional conformal field theories with two boundaries and three-dimensional anti-de Sitter space with two Karch-Randall branes. We compute the entanglement entropy of a bipartition of the BCFT, on both the gravity side and the field theory side. At finite temperature this entanglement entropy characterizes the communication between two braneworld black holes, coupled to each other through a common bath. We find a Page curve consistent with unitarity. The gravitational result, computed using double-holographically realized quantum extremal surfaces, matches the conformal field theory calculation. At zero temperature, we obtain an interesting extension of the AdS$_3$/BCFT$_2$ correspondence. For a central charge $c$, we find a gap $(\frac{c}{16},\frac{c}{12})$ in the spectrum of the scaling dimension $Δ_{\text{bcc}}$ of the boundary condition changing operator (which interpolates mismatched boundary conditions on the two boundaries of the BCFT). Depending on the value of $Δ_{\text{bcc}}$, the gravitational dual is either a defect global AdS$_3$ geometry or a single sided black hole, and in both cases there are two Karch-Randall branes.

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arXiv2021

Searching for Elusive Dark Sectors with Terrestrial and Celestial Observations

We consider the possible existence of a SM-neutral and light dark sector coupled to the visible sector through irrelevant portal interactions. Scenarios of this kind are motivated by dark matter and arise in various extensions of the Standard Model. We characterize the dark dynamics in terms of one ultraviolet scale $Λ_\text{UV}$, at which the exchange of heavy mediator fields generates the portal operators, and by one infrared scale $Λ_\text{IR}$, setting the mass gap. At energies $Λ_\text{IR} \ll E \ll Λ_\text{UV}$ the dark sector behaves like a conformal field theory and its phenomenology can be studied model independently. We derive the constraints set on this scenario by high- and low-energy laboratory experiments and by astrophysical observations. Our results are conservative and serve as a minimum requirement that must be fulfilled by the broad class of models satisfying our assumptions, of which we give several examples. The experimental constraints are derived in a manner consistent with the validity of the effective field theory used to define the portal interactions. We find that high-energy colliders give the strongest bounds and exclude UV scales up to a few TeV, but only in specific ranges of the IR scale. The picture emerging from current searches can be taken as a starting point to design a future experimental strategy with broader sensitivity.

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arXiv2019

Mass Agnostic Jet Taggers

Searching for new physics in large data sets needs a balance between two competing effects---signal identification vs background distortion. In this work, we perform a systematic study of both single variable and multivariate jet tagging methods that aim for this balance. The methods preserve the shape of the background distribution by either augmenting the training procedure or the data itself. Multiple quantitative metrics to compare the methods are considered, for tagging 2-, 3-, or 4-prong jets from the QCD background. This is the first study to show that the data augmentation techniques of Planing and PCA based scaling deliver similar performance as the augmented training techniques of Adversarial NN and uBoost, but are both easier to implement and computationally cheaper.

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arXiv2019

AdS Asymptotic Symmetries from CFT Mirrors

We study Kac-Moody asymptotic symmetries and memory effects in $\text{AdS}_4^{\text{Poincare}}$ gauge theory and (when accompanied by 4D gravity) in its holographic CFT$_3$ dual. While such infinite-dimensional symmetries are absent in standard asymptotic analyses of $\text{AdS}_4$, we show how they arise with alternate AdS boundary conditions. In the 3D holographic description, these alternate boundary conditions correspond to a modified $\widetilde{\text{CFT}}_3$ obtained by Chern-Simons gauging of the CFT$_3$ dual defined by standard boundary conditions, so that Kac-Moody symmetries then follow from the familiar Chern-Simons/Wess-Zumino-Witten correspondence. Apart from their own intrinsic interest, in abelian $\text{AdS}_4$ gauge theories these alternate boundary conditions are equivalent to standard boundary conditions imposed on electric-magnetic dual variables. In the holographic description this corresponds to 3D "mirror" symmetries connecting the original and modified CFTs. Further, in both abelian and non-abelian theories we show that the alternative/$\widetilde{\text{CFT}}_3$ theory emerges at leading order in large Chern-Simons level from the correlators of the standard theory, upon incorporating large-wavelength limits in the holographically emergent dimension. We point out similarities and differences between 4D AdS and Minkowski gauge theories in their asymptotic symmetries, "soft" limits and memory effects.

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