arXiv subjects

Daniele S. M. Alves

Publications and source records attributed to Daniele S. M. Alves.

At least 19 recordsLinked to original sources

arXiv2024

Entanglement Renormalization for Quantum Field Theories with Discrete Wavelet Transforms

We propose an adaptation of Entanglement Renormalization for quantum field theories that, through the use of discrete wavelet transforms, strongly parallels the tensor network architecture of the \emph{Multiscale Entanglement Renormalization Ansatz} (a.k.a. MERA). Our approach, called wMERA, has several advantages of over previous attempts to adapt MERA to continuum systems. In particular, (i) wMERA is formulated directly in position space, hence preserving the quasi-locality and sparsity of entanglers; and (ii) it enables a built-in RG flow in the implementation of real-time evolution and in computations of correlation functions, which is key for efficient numerical implementations. As examples, we describe in detail two concrete implementations of our wMERA algorithm for free scalar and fermionic theories in (1+1) spacetime dimensions. Possible avenues for constructing wMERAs for interacting field theories are also discussed.

hep-th↗

arXiv2024

Final state rescattering effects in axio-hadronic $η$ and $η^{\prime}$ decays

It has been long-understood that final state rescattering effects provide $\mathcal{O}(1)$ corrections to hadronic meson decays rates, such as $η\toπππ$ and $η^{\prime}\toηππ$. Hence, one would expect that such effects would be just as important in axio-hadronic $η$ and $η^{\prime}$ decays, such as $η^{(\prime)}\toππa$, where $a$ is an axion or axion-like particle (ALP). And indeed they are, as we show in this paper by using the treatment of dispersion relations to include the effects of strong final state interactions in several axio-hadronic processes, namely, $η^{(\prime)}\toπ^0π^0 a$, $η^{(\prime)}\toπ^+π^- a$, and $η^{\prime}\toηπ^0 a$. We also compute the perturbative, leading order decay rates for multiple ALP emission, such as in $η^{(\prime)}\toπ^{0}aa$, $η^{\prime}\toηaa$ and $η^{(\prime)}\to aaa$, and briefly discuss the expected corrections from strong interactions and the processes that must be considered for an accurate rate estimation of these multi-ALP decay channels.

hep-ph↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2022

Quasi-Sterile Neutrinos from Dark Sectors I. BSM matter effects in neutrino oscillations and the short-baseline anomalies

Quasi-sterile neutrinos are a natural consequence of dark sectors interacting with the Standard Model (SM) sector via neutrino- and vector-portals. Essentially, quasi-sterile neutrinos are light dark sector fermions with two generic properties: (i) they mix with the active neutrinos of the SM, and (ii) they are charged under a vector mediator that couples feebly to SM matter. Various interesting phenomenological consequences result from this class of particles. In this article, we investigate one such consequence: new, beyond the SM matter effects that can alter in-medium neutrino oscillations. In particular, for special windows of energy and matter densities, active neutrinos can resonantly oscillate into sterile neutrinos. We take advantage of this feature to build a quasi-sterile neutrino model that can explain the MiniBooNE and LSND anomalies, while remaining compatible with observations from long-baseline reactor- and accelerator-based neutrino experiments. This model is also likely compatible with the recent results reported by the MicroBooNE collaboration (albeit we cannot precisely quantify this claim due to a lack of information in MicroBooNE's public data releases to date). Implications for solar neutrinos and $ν_e$ disappearance searches are also briefly discussed.

hep-ph↗

arXiv2021

Signals of the QCD axion with mass of 17 MeV/c^2: nuclear transitions and light meson decays

The QCD axion remains experimentally viable in the mass range of O(10 MeV) if (i) it couples predominantly to the first generation of SM fermions; (ii) it decays to $e^+ e^-$ with a short lifetime $τ_a\lesssim 10^{-13}\,$s; and (iii) it has suppressed isovector couplings, i.e., if it is piophobic. Remarkably, these are precisely the properties required to explain recently observed anomalies in nuclear de-excitations, to wit: the $e^+e^-$ emission spectra of isoscalar magnetic transitions of $^{8\!}$Be and $^{4\!}$He nuclei showed a "bump-like" feature peaked at $m_{e^+e^-}\sim 17$ MeV. In this article, we argue that on-shell emission of the QCD axion (with the aforementioned properties) provides an extremely well-motivated, compatible explanation for the observed excesses in these nuclear de-excitations. The absence of anomalous features in other measured transitions is also naturally explained: piophobic axion emission is strongly suppressed in isovector magnetic transitions, and forbidden in electric transitions. This QCD axion hypothesis is further corroborated by an independent observation: a $2-3\,σ$ deviation in the measurement of $Γ(π^0\to e^+e^-)$ from the Standard Model theoretical expectation. This article also includes detailed estimations of various axionic signatures in rare light meson decays, which take into account contributions from low-lying QCD resonance exchange, and, in the case of rare Kaon decays, the possible effective implementations of $ΔS=1$ octet enhancement in chiral perturbation theory. These inherent uncertainties of the effective description of the strong interactions at low energies result in large variations in the predictions for hadronic signals of the QCD axion; in spite of this, the estimated ranges for rare meson decay rates obtained here can be probed in the near future in $η/η^\prime$ and Kaon factories.

hep-ph↗

arXiv2020

A viable QCD axion in the MeV mass range

The QCD axion is one of the most compelling solutions of the strong CP problem. There are major current efforts into searching for an ultralight, invisible axion, which is believed to be the only phenomenologically viable realization of the QCD axion. Visible axions with decay constants at or below the electroweak scale are believed to have been long excluded by laboratory searches. Considering the significance of the axion solution of the strong CP problem, we revisit experimental constraints on QCD axions in the O(10 MeV) mass window. In particular, we find a variant axion model that remains compatible with existing constraints. This model predicts new states at the GeV scale coupled hadronically, and a variety of low-energy axion signatures, such as rare meson decays, nuclear de-excitations via axion emission, production in $e^+e^-$ annihilation and fixed target experiments. This reopens the possibility of solving the strong CP problem at the GeV scale.

hep-ph↗

arXiv2017

Charged Higgs Signals in $t\,\overline{t}\,H$ Searches

New scalars from an extended Higgs sector could have weak scale masses and still have escaped detection. In a Type I Two Higgs Doublet Model, for instance, even the charged Higgs can be lighter than the top quark. Because electroweak production of these scalars is modest, the greatest opportunity for their detection might come from rare top decays. For mass hierarchies of the type $m_t>m_{H^\pm}>m_{A^0,\,H^0}$, the natural signal can arise from top quark pair production, followed by the decay chain $t \rightarrow b\,H^+$, $H^+ \rightarrow W^{+(*)} ϕ^0$, $ϕ^0\rightarrow b\overline{b},\,τ^+τ^-$, where $ϕ^0=A^0,\,H^0$. These final states largely overlap with those of the Standard Model $t\,\bar{t}\,H^0_{_\text{SM}}$ process, and therefore can potentially contaminate $t\,\bar{t}\,H^0_{_\text{SM}}$ searches. We demonstrate that existing $t\,\bar{t}\,H^0_{_\text{SM}}$ analyses can already probe light extended Higgs sectors, and we derive new constraints from their results. Furthermore, we note that existing excesses in $t\,\bar{t}\,H^0_{_\text{SM}}$ searches can be naturally explained by the contamination of rare top decays to new light Higgses. We discuss how to distinguish this signal from the Standard Model process.

hep-ph↗

arXiv2015

Goldstone Gauginos

Models of supersymmetry with Dirac gauginos provide an attractive scenario for physics beyond the standard model. The "supersoft" radiative corrections and suppressed SUSY production at colliders provide for more natural theories and an understanding of why no new states have been seen. Unfortunately, these models are handicapped by a tachyon which is naturally present in existing models of Dirac gauginos. We argue that this tachyon is absent, with the phenomenological successes of the model preserved, if the right handed gaugino is a (pseudo-)Goldstone field of a spontaneously broken anomalous flavor symmetry.

hep-ph↗

arXiv2015

Models of Goldstone Gauginos

Models with Dirac gauginos provide appealing scenarios for physics beyond the standard model. They have smaller radiative corrections to the Higgs mass, a suppression of certain SUSY production processes, and ameliorated flavor constraints. Unfortunately, they also generally have tachyons, the solutions to which typically spoil these positive features. The recently proposed "Goldstone Gaugino" mechanism provides a simple solution that eliminates these tachyonic states. We provide details on this mechanism and explore models for its origin. In particular, we find SUSY QCD models that realize this idea simply, and discuss scenarios for unification.

hep-ph↗

arXiv2015

Running Electroweak Couplings as a Probe of New Physics

The energy dependence of the electroweak gauge couplings has not been measured above the weak scale. We propose that percent-level measurements of the energy dependence of $α_{1,2}$ can be performed now at the LHC and at future higher energy hadron colliders. These measurements can be used to set limits on new particles with electroweak quantum numbers without relying on any assumptions about their decay properties. The shape of the high invariant mass spectrum of Drell-Yan, $p p \rightarrow Z^*/γ^* \rightarrow \ell^+ \ell^-$, constrains $α_{1,2}(Q)$, and the shape of the high transverse mass distribution of $p p \rightarrow W^* \rightarrow \ell ν$ constrains $α_{2}(Q)$. We use existing data to perform the first fits to $α_{1,2}$ above the weak scale. Percent-level measurements are possible because of high precision in theoretical predictions and existing experimental measurements. We show that the LHC already has the reach to improve upon electroweak precision tests for new particles that dominantly couple through their electroweak charges. The 14 TeV LHC is sensitive to the predicted Standard Model (SM) running of $α_2$, and can show that $α_2$ decreases with energy at $2-3 σ$ significance. A future 100 TeV proton-proton collider will have significant reach to measure running weak couplings, with sensitivity to the SM running of $α_2$ at $4-5 σ$ and sensitivity to winos with masses up to $\sim$ 1.3 TeV at $2σ$.

hep-ph↗

arXiv2013

Hiding Missing Energy in Missing Energy

Searches for supersymmetry (SUSY) often rely on a combination of hard physics objects (jets, leptons) along with large missing transverse energy to separate New Physics from Standard Model hard processes. We consider a class of ``double-invisible'' SUSY scenarios: where squarks, stops and sbottoms have a three-body decay into two (rather than one) invisible final-state particles. This occurs naturally when the LSP carries an additional conserved quantum number under which other superpartners are not charged. In these topologies, the available energy is diluted into invisible particles, reducing the observed missing energy and visible energy. This can lead to sizable changes in the sensitivity of existing searches, dramatically changing the qualitative constraints on superpartners. In particular, for m_LSP>160 GeV, we find no robust constraints from the LHC at any squark mass for any generation, while for lighter LSPs we find significant reductions in constraints. If confirmed by a full reanalysis from the collaborations, such scenarios allow for the possibility of significantly more natural SUSY models. While not realized in the MSSM, such phenomenology occurs naturally in models with mixed sneutrinos, Dirac gauginos and NMSSM-like models.

hep-ph↗

arXiv2012

Stops and MET: the shape of things to come

LHC experiments have placed strong bounds on the production of supersymmetric colored particles (squarks and gluinos), under the assumption that all flavors of squarks are nearly degenerate. However, the current experimental constraints on stop squarks are much weaker, due to the smaller production cross section and difficult backgrounds. While light stops are motivated by naturalness arguments, it has been suggested that such particles become nearly impossible to detect near the limit where their mass is degenerate with the sum of the masses of their decay products. We show that this is not the case, and that searches based on missing transverse energy (MET) have significant reach for stop masses above 175 GeV, even in the degenerate limit. We consider direct pair production of stops, decaying to invisible LSPs and tops with either hadronic or semi-leptonic final states. Modest intrinsic differences in MET are magnified by boosted kinematics and by shape analyses of MET or suitably-chosen observables related to MET. For these observables we show that the distributions of the relevant backgrounds and signals are well-described by simple analytic functions, in the kinematic regime where signal is enhanced. Shape analyses of MET-related distributions will allow the LHC experiments to place significantly improved bounds on stop squarks, even in scenarios where the stop-LSP mass difference is degenerate with the top mass. Assuming 20/fb of luminosity at 8 TeV, we conservatively estimate that experiments can exclude or discover degenerate stops with mass as large as ~ 360 GeV and 560 GeV for massless LSPs.

hep-ph↗

arXiv2012

Higgs Signals in a Type I 2HDM or with a Sister Higgs

In models where an additional SU(2)-doublet that does not have couplings to fermions participates in electroweak symmetry breaking, the properties of the Higgs boson are changed. At tree level, in the neighborhood of the SM-like range of parameter space, it is natural to have the coupling to vectors, cV, approximately constant, while the coupling to fermions, cf, is suppressed. This leads to enhanced VBF signals of gamma gamma while keeping other signals of Higgses approximately constant (such as WW* and ZZ*), and suppressing higgs to tau tau. Sizable tree-level effects are often accompanied by light charged Higgs states, which lead to important constraints from b to s gamma and top to b H+, but also often to similarly sizable contributions to the inclusive h to gamma gamma signal from radiative effects. In the simplest model, this is described by a Type I 2HDM, and in supersymmetry is naturally realized with "sister Higgs" fields. In such a scenario, additional light charged states can contribute further with fewer constraints from heavy flavor decays. With supersymmetry, Grand Unification motivates the inclusion of colored partner fields. These G-quarks may provide additional evidence for such a model.

hep-ph↗

arXiv2012

Supersymmetry with a Sister Higgs

Within the context of supersymmetric theories, explaining a 125 GeV Higgs motivates a consideration of a broader range of models. We consider a simple addition to the MSSM of a "Sister Higgs" ($Σ_d$), a Higgs field that participates in electroweak symmetry breaking but does not give any direct masses to Standard Model matter fields. While a relatively minor addition, the phenomenological implications can be important. Such a field can be naturally charged under an additional symmetry group $G_s$. If gauged, the Higgs mass is naturally much larger than in the MSSM through an NMSSM-type interaction, but with $Σ_d$ playing the role of $H_d$. The addition of the sister Higgs allows new R-parity violating operators $Σ_d H_d E$, which are less constrained than conventional leptonic R-parity violation. Considerations of unification motivates the presence of colored $G_s$-charged fields. Production of these G-quarks can lead to new b-rich final states and modifications to decays of gluinos, as well as new opportunities for R-parity violation. Unlike a conventional fourth generation, G-quarks dominantly decay into a light jet and a scalar (potentially the Higgs), which then generally decays to b-jets. The presence of additional sister charges allows the possibilities that lightest sister-charged particle (LSiP) could be stable. We consider the possibility of an LSiP dark matter candidate and find it is generally very constrained.

hep-ph↗

arXiv2012

Dark Matter in 3D

We discuss the relevance of directional detection experiments in the post-discovery era and propose a method to extract the local dark matter phase space distribution from directional data. The first feature of this method is a parameterization of the dark matter distribution function in terms of integrals of motion, which can be analytically extended to infer properties of the global distribution if certain equilibrium conditions hold. The second feature of our method is a decomposition of the distribution function in moments of a model independent basis, with minimal reliance on the ansatz for its functional form. We illustrate our method using the Via Lactea II N-body simulation as well as an analytical model for the dark matter halo. We conclude that O(1000) events are necessary to measure deviations from the Standard Halo Model and constrain or measure the presence of anisotropies.

astro-ph.GA↗

arXiv2011

Where the Sidewalk Ends: Jets and Missing Energy Search Strategies for the 7 TeV LHC

This work explores the potential reach of the 7 TeV LHC to new colored states in the context of simplified models and addresses the issue of which search regions are necessary to cover an extensive set of event topologies and kinematic regimes. This article demonstrates that if searches are designed to focus on specific regions of phase space, then new physics may be missed if it lies in unexpected corners. Simple multiregion search strategies can be designed to cover all of kinematic possibilities. A set of benchmark models are created that cover the qualitatively different signatures and a benchmark multiregion search strategy is presented that covers these models.

hep-ph↗

arXiv2011

Higgs, Binos and Gluinos: Split Susy Within Reach

Recent evidence from the LHC for the Higgs boson with mass between 142 GeV < m_h < 147GeV points to PeV-scale Split Supersymmetry. This article explores the consequences of a Higgs mass in this range and possible discovery modes for Split Susy. Moderate lifetime gluinos, with decay lengths in the 25 microns to 10 years range, are its imminent smoking gun signature. The 7 TeV LHC will be sensitive to the moderately lived gluinos and trilepton signatures from direct electroweakino production. Moreover, the dark matter abundance may be obtained from annihilation through an s-channel Higgs resonance, with the LSP almost purely bino and mass m_chi = 70 GeV. The Higgs resonance region of Split Susy has visible signatures in dark matter direct and indirect detection and electric dipole moment experiments. If the anomalies go away, the majority of Split Susy parameter space will be excluded.

hep-ph↗

arXiv2011

It's On: Early Interpretations of ATLAS Results in Jets and Missing Energy Searches

The first search for supersymmetry from ATLAS with 70/nb of integrated luminosity extends the Tevatron' s reach for colored particles that decay into jets plus missing transverse energy. For gluinos that decay directly or through a one step cascade into the LSP and two jets, the mass range m_g < 205 GeV is disfavored by the ATLAS searches, regardless of the mass of the LSP. In some cases the coverage extends up to m_g ~ 295 GeV, already surpassing the Tevatron's reach for compressed supersymmetry spectra.

hep-ph↗