Ayan PaulDESY, Hamburg & Humboldt Universität zu Berlin
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PROFILE

PERSONAL DETAILS

DESY, Notkestra. 85, 22607 Hamburg, Germany
+393348094805
Hello. I am a Researcher Physicist Thinker Creator
I work as a Theoretical Particle Physicist
looking at the world of Flavour and Higgs Physics Specialist in Physics Computing

PHYSICS

THEORETICAL PARTICLE PHYSICS

The trade of Particle Physics phenomenology has arrived at a stage where the broader landscape of the field has become a necessary scope of exploration. With signatures of new dynamics continuing to be somewhat elusive, it has become important to study not only dynamics of different possible extensions of the Standard Theory, but also interconnect the different "puzzles" that have arisen from the theoretical and experimental fronts in areas that are typically separated as distinct disciplines within Particle Physics phenomenology itself.

My participation in physics has involved both the study of dynamics at scales ranging from the GeV to the TeV and the development of computational tools that can be used for precision study of experimental results vis-à-vis theoretical constructs. My experience in flavour dynamics and Higgs physics allows me to aim at building a broader landscape using dynamics from several scales. My work has not only given me a good understanding of physics at various scales but has also allowed me to gain significant experience in the development and use of computational tools of a broad range of applicability. Somewhere in this spread of scales lies the key to the puzzle of scale separations and the answers that will fill a part of the void in our knowledge of fundamental dynamics in the TeV regime and beyond.



PHYSICS OF INTELLIGENCE

An Interview with Dr. Maria Hoffacker:



AREAS OF EXPERTISE

Charm dynamics: CP violation, hadronic decays, final state interactions, leptonic and semileptonic decays.

Beauty dynamics: Semileptonic and leptonic decays, decay distributions, tests of lepton flavour universality and BSM

Higgs and electroweak Physics: Effective Field Theories, Higgs productions and decays, BSM and future colliders

Physics Computation: Active developer for the statistical core (MCMC based Bayesian Analysis) and flavour physics in $\texttt{HEPfit}$

$\texttt{HEPfit}$

a Code for the Combination of Indirect and Direct Constraints on High Energy Physics Models.

Higgs Physics
The Higgs program of $\texttt{HEPfit}$ includes the study of signal strengths for both current and future colliders. Analyses can be done for constraints on new physics models like THDM and for parameters of an effective field theory like SMEFT.

Precision Electroweak
Tests of electroweak precision observables can severely constrain the available parameter space of new physics model. These tests are included in $\texttt{HEPfit}$ for models and EFT frameworks.

Flavour Physics
The Flavour Physics menu in $\texttt{HEPfit}$ includes both quark and lepton flavour dynamics and has lead to several important analysis of Standard Model hadronic effects and constraints on EFT frameworks and models beyond the Standard Model.

BSM Physics
Dynamics beyond the Standard Model can be studied by adding models in $\texttt{HEPfit}$. Several new physics models are already built in and others can be implemented for a variety of analyses.

$\mathbf{\texttt{HEPfit}}$ website: https://hepfit.roma1.infn.it
$\mathbf{\texttt{HEPfit}}$ repository: https://github.com/silvest/HEPfit

OUTREACH ACTIVITIES

PHYSICS ADMINISTRATION AND TRANSFER OF KNOWLEDGE

7
Plenary Talks
15
Invited Talks
21
Seminars
17
Contributed Talks
41
Workshops and Conferences
Convener (WG7)
CKM 2016
Representative
Graduate Students Union
Founder
Graduate Physics Students Association
Founder
GPS Summer Conferences
Judge
Science Fairs for School Students
Content Editor
Global Editions @ Pearson's Education

.02

PROFESSION & EDUCATION

  • ACADEMIC AND PROFESSIONAL POSITIONS
  • 2017
    Berlin, Germany

    FELLOW

    DESY, HAMBURG

    SENIOR SCIENTIST

    HUMBOLDT UNIVERSITÄT ZU BERLIN

  • 2020
    BERLIN, GERMANY

    CO-FOUNDER & CHIEF SCIENTIFIC OFFICER

    CoVis

    USA & GERMANY
  • 2012
    2017
    ROMA, ITALY

    ASSEGNISTA DI RICERCA

    INFN, SEZIONE DI ROMA I

    ERC GRANT "NPFLAVOUR"
  • 2005
    2011
    Notre Dame, IN USA

    TEACHING ASSISTANT

    UNIVERSITY OF NOTRE DAME DU LAC

    Assisted with several graduate and undergraduate course and laboratory classes
  • DEGREES
  • 2012
    Notre Dame, IN USA

    PHYSICS - PHD

    UNIVERSITY OF NOTRE DAME DU LAC

    Thesis: Charm Beyond the Standard Model Adviser: Prof. Ikaros I. Bigi
  • 2007
    Notre Dame, IN USA

    PHYSICS - MS

    UNIVERSITY OF NOTRE DAME DU LAC

    Department of Physics
  • 2005
    Calcutta, India

    PHYSICS - M. Sc.

    S N BOSE NATIONAL CENTER FOR BASIC SCIENCES

    Department of Physics
  • 2002
    Calcutta, India

    PHYSICS - B. Sc.

    PRESIDENCY COLLEGE, UNIVERSITY OF CALCUTTA

    Physics, Mathematics and Statistics
.03

PUBLICATIONS

LIST OF SELECTED PUBLICATIONS
ALL
SORTING BY DATE
14 December 2020

The Anomalous Case of Axion EFTs and Massive Chiral Gauge Fields

JHEP 05 (2021) 153

Formal Theory Journal paper Q. Bonnefoy, L. Di Luzio, C. Grojean, A. Paul and A. N. Rossia

The Anomalous Case of Axion EFTs and Massive Chiral Gauge Fields

Q. Bonnefoy, L. Di Luzio, C. Grojean, A. Paul, A. N. Rossia

JHEP 05 (2021) 153

Formal Theory

We study axion effective field theories (EFTs), with a focus on axion couplings to massive chiral gauge fields. We investigate the EFT interactions that participate in processes with an axion and two gauge bosons, and we show that, when massive chiral gauge fields are present, such interactions do not entirely originate from the usual anomalous EFT terms. We illustrate this both at the EFT level and by matching to UV-complete theories. In order to assess the consistency of the Peccei--Quinn (PQ) anomaly matching, it is useful to introduce an auxiliary, non-dynamical gauge field associated to the PQ symmetry. When applied to the case of the Standard Model (SM) electroweak sector, our results imply that anomaly-based sum rules between EFT interactions are violated when chiral matter is integrated out, which constitutes a smoking gun of the latter. As an illustration, we study a UV-complete chiral extension of the SM, containing an axion arising from an extended Higgs sector and heavy fermionic matter that obtains most of its mass by coupling to the Higgs doublets. We assess the viability of such a SM extension through electroweak precision tests, bounds on Higgs rates and direct searches for heavy charged matter. At energies below the mass of the new chiral fermions, the model matches onto an EFT where the electroweak gauge symmetry is non-linearly realised.

01 December 2020

Resurrecting $b\bar{b}h$ with kinematic                         

JHEP 04 (2021) 139

Higgs Physics Machine Learning Journal paper C. Grojean, A. Paul and Z. Qian

Resurrecting $b\bar{b}h$ with kinematic

C. Grojean, A. Paul and Z. Qian

JHEP 04 (2021) 139

Higgs Physics Machine Learning

The associated production of a $b\bar{b}$ pair with a Higgs boson could provide an important probe to both the size and the phase of the bottom-quark Yukawa coupling, yb. However, the signal is shrouded by several background processes including the irreducible $Zh,Z\to b\bar{b}$ background. We show that the analysis of kinematic shapes provides us with a concrete prescription for separating the $y_b$-sensitive production modes from both the irreducible and the QCD-QED backgrounds using the $b\bar{b}\gamma\gamma$ final state. We draw a page from game theory and use Shapley values to make Boosted Decisions Trees interpretable in terms of kinematic measurables and provide physics insights into the variances in the kinematic shapes of the different channels that help us complete this feat. Adding interpretability to the machine learning algorithm opens up the black-box and allows us to cherry-pick only those kinematic variables that matter most in the analysis. We resurrect the hope of constraining the size and, possibly, the phase of $y_b$ using kinematic shape studies of $b\bar{b}h$ production with the full HL-LHC data and FCC-hh.

19 November 2020

The Anomalous Case of Axion EFTs and Massive Chiral Gauge Fields

JHEP 07 (2021) 189

Formal Theory Journal paper Q. Bonnefoy, L. Di Luzio, C. Grojean, A. Paul and A. N. Rossia

The Anomalous Case of Axion EFTs and Massive Chiral Gauge Fields

Q. Bonnefoy, L. Di Luzio, C. Grojean, A. Paul, A. N. Rossia

JHEP 07 (2021) 189

Formal Theory

We study axion effective field theories (EFTs), with a focus on axion couplings to massive chiral gauge fields. We investigate the EFT interactions that participate in processes with an axion and two gauge bosons, and we show that, when massive chiral gauge fields are present, such interactions do not entirely originate from the usual anomalous EFT terms. We illustrate this both at the EFT level and by matching to UV-complete theories. In order to assess the consistency of the Peccei--Quinn (PQ) anomaly matching, it is useful to introduce an auxiliary, non-dynamical gauge field associated to the PQ symmetry. When applied to the case of the Standard Model (SM) electroweak sector, our results imply that anomaly-based sum rules between EFT interactions are violated when chiral matter is integrated out, which constitutes a smoking gun of the latter. As an illustration, we study a UV-complete chiral extension of the SM, containing an axion arising from an extended Higgs sector and heavy fermionic matter that obtains most of its mass by coupling to the Higgs doublets. We assess the viability of such a SM extension through electroweak precision tests, bounds on Higgs rates and direct searches for heavy charged matter. At energies below the mass of the new chiral fermions, the model matches onto an EFT where the electroweak gauge symmetry is non-linearly realised.

27 September 2020

Beyond COVID-19: Network science and sustainable exit strategies

J. Phys. Complex. 2 021001

Epidemiology Journal paper J. Bell et al.

Beyond COVID-19: Network science and sustainable exit strategies

J. Bell et al.

J. Phys. Complex. 2 021001

Epidemiology Journal paper

On May 28th and 29th, a two day workshop was held virtually, facilitated by the Beyond Center at ASU and Moogsoft Inc. The aim was to bring together leading scientists with an interest in Network Science and Epidemiology to attempt to inform public policy in response to the COVID-19 pandemic. Epidemics are at their core a process that progresses dynamically upon a network, and are a key area of study in Network Science. In the course of the workshop a wide survey of the state of the subject was conducted. We summarize in this paper a series of perspectives of the subject, and where the authors believe fruitful areas for future research are to be found.

10 September 2020

Socio-economic disparities and COVID-19 in the USA

J. Phys. Complex. 2 035017

Epidemiology Journal paper A. Paul, P. Englert and M. Varga

Socio-economic disparities and COVID-19 in the USA

A. Paul, P. Englert and M. Varga

J. Phys. Complex. 2 035017

Epidemiology

COVID-19 is not a universal killer. We study the spread of COVID-19 at the county level for the United States up until the 15th of August, 2020. We show that the prevalence of the disease and the death rate are correlated with the local socio-economic conditions often going beyond local population density distributions, especially in rural areas. We correlate the COVID-19 prevalence and death rate with data from the US Census Bureau and point out how the spreading patterns of the disease show asymmetries in urban and rural areas separately and is preferentially affecting the counties where a large fraction of the population is non-white. Our findings can be used for more targeted policy building and deployment of resources for future occurrence of a pandemic due to SARS-CoV-2. Our methodology, based on interpretable machine learning and game theory, can be extended to study the spread of other diseases.

8 July 2020

$B$ anomalies under the lens of electroweak precision

JHEP 12 (2020) 016

Flavour Physics Journal Paper L. Alasfar, A. Azatov, J. de Blas, A. Paul, M. Valli

$B$ anomalies under the lens of electroweak precision

L. Alasfar, A. Azatov, J. de Blas, A. Paul, M. Valli

JHEP 12 (2020) 016

Flavour Physics Electroweak Physics

The measurements carried out at LEP and SLC projected us into the precision era of electroweak physics. This has also been relevant in the theoretical interpretation of LHCb and Belle measurements of rare $B$ semileptonic decays, paving the road for new physics with the inference of lepton universality violation in $R_{K^{(*)}}$ ratios. The simplest explanation of these flavour anomalies -- sizeable one-loop contributions respecting Minimal Flavour Violation -- is currently disfavoured by electroweak precision data. In this work, we discuss how to completely relieve the present tension between electroweak constraints and one-loop minimal flavour violating solutions to $R_{K^{(*)}}$. We determine the correlations in the Standard Model Effective Field Theory that highlight the existence of such a possibility. Then, we consider minimal extensions of the Standard Model where our effective-field-theory picture can be realized. We discuss how these solutions to $b \to s \ell \ell$ anomalies, respecting electroweak precision and without any new source of flavour violation, may point to the existence of a $Z^{\prime}$ boson at around the TeV scale, within the discovery potential of LHC, or to leptoquark scenarios.

20 April 2020

Contact Tracing: a game of big numbers in the time of COVID-19

J. R. Soc. Interface.18:20200954

Epidemiology Journal paper H. Kim and A. Paul

Contact Tracing: a game of big numbers in the time of COVID-19

H. Kim and A. Paul

J. R. Soc. Interface.18:20200954

Epidemiology Journal paper

One of the more widely advocated solutions to slowing down the spread of COVID-19 has been automated contact tracing. Since proximity data can be collected by personal mobile devices, the natural proposal has been to use this for contact tracing as this provides a major gain over a manual implementation. In this work, we study the characteristics of automated contact tracing and its effectiveness for mapping the spread of a pandemic due to the spread of SARS-CoV-2. We highlight the infrastructure and social structures required for automated contact tracing to work for the current pandemic. We display the vulnerabilities of the strategy to inadequately sample the population, which results in the inability to sufficiently determine significant contact with infected individuals. Of crucial importance will be the participation of a significant fraction of the population for which we derive a minimum threshold. We conclude that a strong reliance on contact tracing to contain the spread of the SARS-CoV-2 pandemic can lead to the potential danger of allowing the pandemic to spread unchecked. A carefully thought out strategy for controlling the spread of the pandemic along with automated contact tracing can lead to an optimal solution

31 October 2019

$\texttt{HEPfit}$: a Code for the Combination of Indirect and Direct Constraints on High Energy Physics Models

Eur. Phys. J. C 80 (2020) 5

Computational Physics Journal Paper J. De Blas et. al.

$\tt{HEPfit}$: a Code for the Combination of Indirect and Direct Constraints on High Energy Physics Models

J. De Blas et. al.

Eur. Phys. J. C 80 (2020) 5

Computational Physics

$\tt{HEPfit}$ is a flexible open-source tool which, given the Standard Model or any of its extensions, allows to i) fit the model parameters to a given set of experimental observables; ii) obtain predictions for observables. $\texttt{HEPfit}$ can be used either in Monte Carlo mode, to perform a Bayesian Markov Chain Monte Carlo analysis of a given model, or as a library, to obtain predictions of observables for a given point in the parameter space of the model, allowing $\texttt{HEPfit}$ to be used in any statistical framework. In the present version, around a thousand observables have been implemented in the Standard Model and in several new physics scenarios. In this paper, we describe the general structure of the code as well as models and observables implemented in the current release.

9 July 2019

On the future of Higgs, electroweak and diboson measurements at lepton colliders

JHEP 1912 (2019) 117

Higgs Physics Journal Paper J. De Blas, G. Durieux, C. Grojean, J. Gu and A. Paul

On the future of Higgs, electroweak and diboson measurements at lepton colliders

J. De Blas, G. Durieux, C. Grojean, J. Gu and A. Paul

JHEP 1912 (2019) 117

Higgs Physics Electroweak Physics Journal Paper

LEP precision on electroweak measurements was sufficient not to hamper the extraction of Higgs couplings at the LHC. But the foreseen permille-level Higgs measurements at future lepton colliders might suffer from parametric electroweak uncertainties in the absence of a dedicated electroweak program. We perform a joint, complete and consistent effective-field-theory analysis of Higgs and electroweak processes. The full electroweak-sector dependence of the $e^+e^-\to WW$ production process is notably accounted for, using statistically optimal observables. Up-to-date HL-LHC projections are combined with CEPC, FCC-ee, ILC and CLIC ones. For circular colliders, our results demonstrate the importance of a new $Z$-pole program for the robust extraction of Higgs couplings. At linear colliders, we show how exploiting multiple polarizations and centre-of-mass energies is crucial to mitigate contaminations from electroweak parameter uncertainties on the Higgs physics program. We also investigate the potential of alternative electroweak measurements to compensate for the lack of direct $Z$-pole run, considering for instance radiative return to these energies. Conversely, we find that Higgs measurements at linear colliders could improve our knowledge of the $Z$ couplings to electrons.

22 March 2019

New Physics in $b \to s \ell^+ \ell^-$ confronts new data on Lepton Universality

Eur. Phys. J. C79 (2019) no.8, 719

Flavour Physics Journal Paper M. Ciuchini, A. M. Coutinho, M. Fedele, E. Franco,
A. Paul, L. Silvestrini and M. Valli

New Physics in $b \to s \ell^+ \ell^-$ confronts new data on Lepton Universality

M. Ciuchini, A. M. Coutinho, M. Fedele, E. Franco, A. Paul, L. Silvestrini and M. Valli

Eur. Phys. J. C79 (2019) no.8, 719

Flavour Physics Journal Paper

In light of the very recent updates on the $R_K$ and $R_{K^*}$ measurements from the LHCb and Belle collaborations, we systematically explore here imprints of New Physics in $b \rightarrow s \ell ^+ \ell ^- $ transitions using the language of effective field theories. We focus on effects that violate Lepton Flavour Universality both in the Weak Effective Theory and in the Standard Model Effective Field Theory. In the Weak Effective Theory we find a preference for scenarios with the simultaneous presence of two operators, a left-handed quark current with vector muon coupling and a right-handed quark current with axial muon coupling, irrespective of the treatment of hadronic uncertainties. In the Standard Model Effective Field Theory we select different scenarios according to the treatment of hadronic effects: while an aggressive estimate of hadronic uncertainties points to the simultaneous presence of two operators, one with left-handed quark and muon couplings and one with left-handed quark and right-handed muon couplings, a more conservative treatment of hadronic matrix elements leaves room for a broader set of scenarios, including the one involving only the purely left-handed operator with muon coupling.

14 February 2019

$SU(3)_F$ breaking through final state interactions and $CP$ asymmetries in $D \to PP$ decays

Phys. Rev. D99 (2019) no.11, 113001

Flavour Physics Journal Paper F. Buccella, A. Paul and P. Santorelli

$SU(3)_F$ breaking through final state interactions and $CP$ asymmetries in $D \to PP$ decays

F. Buccella, A. Paul and P. Santorelli

Phys. Rev. D99 (2019) no.11, 113001

Flavour Physics Journal Paper

We analyze D decays to two pseudoscalars (π,K) assuming the dominant source of SU(3)F breaking lies in final state interactions. We obtain an excellent agreement with experimental data and are able to predict CP violation in several channels based on current data on branching ratios and ΔACP. We also make predictions for δKπ and the branching fraction for the decay Ds+→K+KL. We analyse $D$ decays to two pseudoscalars $(\pi,K)$ assuming the dominant source of $\mathrm{SU}(3)_F$ breaking lies in final state interactions. We obtain an excellent agreement with experimental data and are able to predict CP violation in several channels based on current data on branching ratios and $\Delta \mathrm{A_{CP}}$. We also make predictions for $\delta_{K\pi}$ and the branching fraction for the decay $D_s^+\to K^+K_L$.

5 December 2018

The CLIC Potential for New Physics                      

CERN Yellow Rep. Monogr. Vol. 3 (2018)

Higgs Physics Report J. de Blas et. al.

The CLIC Potential for New Physics

J. de Blas et. al.

CERN Yellow Rep. Monogr. Vol. 3 (2018)

Higgs Physics Report

The Compact Linear Collider (CLIC) is a mature option for the future of high energy physics. It combines the benefits of the clean environment of $e^+e^-$ colliders with operation at high centre-of-mass energies, allowing to probe scales beyond the reach of the Large Hadron Collider (LHC) for many scenarios of new physics. This places the CLIC project at a privileged spot in between the precision and energy frontiers, with capabilities that will significantly extend knowledge on both fronts at the end of the LHC era. In this report we review and revisit the potential of CLIC to search, directly and indirectly, for physics beyond the Standard Model.

30 August 2018

The Belle II Physics Book                                          

B2TiP Report

Flavour Physics Report Belle II Collaboration

The Belle II Physics Book

Belle II Collaboration

B2TiP Report

Flavour Physics Report

We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB $e^+e^-$ collider. Belle II collected its first collisions in 2018, and is expected to operate for the next decade. It is anticipated to collect 50 ab$^{-1}$ of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: $B$ physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic $B$ decays, Radiative and Electroweak penguins, $\phi_1$ and $\phi_2$ (time-dependent CP violation) measurements, $\phi_3$ measurements, Charmless hadronic $B$ decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.

10 October 2017

Heavy Higgs Searches: Flavour Matters               

JHEP 1801 (2018) 108

Higgs Physics Journal Paper S. Gori, C. Grojean, A. Juste and A. Paul

Heavy Higgs Searches: Flavour Matters

S. Gori, C. Grojean, A. Juste and A. Paul

JHEP 1801 (2018) 108

Higgs Physics Journal Paper

We point out that the stringent lower bounds on the masses of additional electrically neutral and charged Higgs bosons crucially depend on the flavour structure of their Yukawa interactions. We show that these bounds can easily be evaded by the introduction of flavour-changing neutral currents in the Higgs sector. As an illustration, we study the phenomenology of a two Higgs doublet model with a Yukawa texture singling out the third family of quarks and leptons. We combine constraints from low-energy flavour physics measurements, LHC measurements of the 125 GeV Higgs boson rates, and LHC searches for new heavy Higgs bosons. We propose novel LHC searches that could be performed in the coming years to unravel the existence of these new Higgs bosons.

18 April 2017

On Flavourful Easter eggs for New Physics hunger and Lepton Flavour Universality violation

Eur. Phys. J. C77 (2017) no.10, 688

Flavour Physics Journal Paper M. Ciuchini, A. M. Coutinho, M. Fedele, E. Franco,
A. Paul, L. Silvestrini and M. Valli

On Flavourful Easter eggs for New Physics hunger and Lepton Flavour Universality violation

M. Ciuchini, A. M. Coutinho, M. Fedele, E. Franco, A. Paul, L. Silvestrini and M. Valli

Eur. Phys. J. C77 (2017) no.10, 688

Flavour Physics Journal Paper

Within the standard approach of effective field theory of weak interactions for $\varDelta B = 1$ transitions, we look for possibly unexpected subtle New Physics effects, here dubbed “flavourful Easter eggs”. We perform a Bayesian global fit using the publicly available HEPfit package, taking into account state-of-the-art experimental information concerning these processes, including the suggestive measurements from LHCb of $R_{K}$ and $R_{K^{*}}$ , the latter available only very recently. We parametrise New Physics contributions to $b \rightarrow s$ transitions in terms of shifts of Wilson coefficients of the electromagnetic dipole and semileptonic operators, assuming CP-conserving effects, but allowing in general for violation of lepton flavour universality. We show how optimistic/conservative hadronic estimates can impact quantitatively the size of New Physics extracted from the fit. With a conservative approach to hadronic uncertainties we find nonzero New Physics contributions to Wilson coefficients at the level of $\sim 3\sigma $ , depending on the model chosen. Furthermore, given the interplay between hadronic contributions and New Physics effects in the leptonic vector current, a scenario with nonstandard leptonic axial currents is comparable to the more widely advocated one with New Physics in the leptonic vector current.

8 August 2016

Constraints on new physics from radiative $B$ decays

JHEP 1704 (2017) 027

Flavour Physics Journal Paper A. Paul and D. M. Straub

Constraints on new physics from radiative $B$ decays

A. Paul and D. M. Straub

JHEP 1704 (2017) 027

Flavour Physics Journal Paper

A new phase for the measurements of radiative decay modes in $b \to s$ transitions has started with new measurements of exclusive modes by LHCb and with Belle-II showing distinctive promises in both inclusive and exclusive channels. After critically reviewing the hadronic uncertainties in exclusive radiative decays, we analyze the impact of recent measurements of the branching ratio and mass-eigenstate rate asymmetry in $B_s\to\phi\gamma$ and of the angular distribution of $B\to K^*e^+e^-$ at low $q^2$ on new physics in the $b\to s\gamma$ transition.

2 August 2016

Resolving gluon fusion loops at current and future hadron colliders

JHEP 1609 (2016) 123

Higgs Physics Journal Paper A. Azatov, C. Grojean, A. Paul and E. Salvioni

Resolving gluon fusion loops at current and future hadron colliders

A. Azatov, C. Grojean, A. Paul and E. Salvioni

JHEP 1609 (2016) 123

Higgs Physics Journal Paper

Inclusive Higgs measurements at the LHC have limited resolution on the gluon fusion loops, being unable to distinguish the long-distance contributions mediated by the top quark from possible short-distance new physics effects. Using an Effective Field Theory (EFT) approach we compare several proposed methods to lift this degeneracy, including $t\bar{t}h$ and boosted, off-shell and double Higgs production, and perform detailed projections to the High-Luminosity LHC and a future hadron collider. In addition, we revisit off-shell Higgs production. Firstly, we point out its sensitivity to modifications of the top-$Z$ couplings, and by means of a general analysis we show that the reach is comparable to that of tree-level processes such as $t\bar{t}Z$ production. Implications for composite Higgs models are also discussed. Secondly, we assess the regime of validity of the EFT, performing an explicit comparison for a simple extension of the Standard Model containing one vector-like quark.

22 December 2015

$B\to K^* \ell^+ \ell^-$ decays at large recoil in the Standard Model: a theoretical reappraisal

JHEP 1606 (2016) 116

Flavour Physics Journal Paper M. Ciuchini, M. Fedele, E. Franco, S. Mishima,
A. Paul, L. Silvestrini and M. Valli

$B\to K^* \ell^+ \ell^-$ decays at large recoil in the Standard Model: a theoretical reappraisal

M. Ciuchini, M. Fedele, E. Franco, S. Mishima, A. Paul, L. Silvestrini and M. Valli

JHEP 1606 (2016) 116

Flavour Physics Journal Paper

We critically reassess the theoretical uncertainties in the Standard Model calculation of the $B \to K^* \ell^+ \ell^-$ observables, focusing on the low $q^2$ region. We point out that even optimized observables are affected by sizable uncertainties, since hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for $q^2 \sim 4 m_c^2\simeq 6.8$ GeV$^2$. We perform a detailed numerical analysis and present both predictions and results from the fit obtained using most recent data. We find that non-factorizable power corrections of the expected order of magnitude are sufficient to give a good description of current experimental data within the Standard Model. We discuss in detail the $q^2$ dependence of the corrections and their possible interpretation as shifts of the Standard Model Wilson coefficients.

24 June 2014

Taming the off-shell Higgs boson                         

J. Exp. Theor. Phys. 120 (2015) 354-368

Higgs Physics Journal Paper A. Azatov, C. Grojean, A. Paul and E. Salvioni

Taming the off-shell Higgs boson

A. Azatov, C. Grojean, A. Paul and E. Salvioni

J. Exp. Theor. Phys. 120 (2015) 354-368

Higgs Physics Journal Paper

We study the off-shell Higgs data in the process $pp\to h^{(*)} \to Z^{(\ast)}Z^{(\ast)}\to 4\ell$, to constrain deviations of the Higgs couplings. We point out that this channel can be used to resolve the long- and short-distance contributions to Higgs production by gluon fusion and can thus be complementary to $pp\to ht\bar t$ in measuring the top Yukawa coupling. Our analysis, performed in the context of Effective Field Theory, shows that current data do not allow one to draw any model-independent conclusions. We study the prospects at future hadron colliders, including the high-luminosity LHC and accelerators with higher-energy, up to 100 TeV. The available QCD calculations and the theoretical uncertainties affecting our analysis are also briefly discussed.

20 September 2014

Probing Higgs couplings with high $p_T$ Higgs production

JHEP 1401 (2014) 014

Higgs Physics Journal Paper A. Azatov and A. Paul

Probing Higgs couplings with high $p_T$ Higgs production

A. Azatov and A. Paul

JHEP 1401 (2014) 014

Higgs Physics Journal Paper

Possible extensions of the Standard Model predict modifications of the Higgs couplings to gluons and to the SM top quark. The values of these two couplings can, in general, be independent. We discuss a way to measure these interactions by studying the Higgs production at high $p_T$ within an effective field theory formalism. We also propose an observable $r_\pm$ with reduced theoretical errors and suggest its experimental interpretation.

19 December 2012

Manifestations of warped extra dimension in rare charm decays and asymmetries

Phys. Rev. D90 (2014) no.1, 014035

Flavour Physics Journal Paper A. Paul, A. De La Puente and I. I. Bigi

Manifestations of warped extra dimension in rare charm decays and asymmetries

A. Paul, A. De La Puente and I. I. Bigi

Phys. Rev. D90 (2014) no.1, 014035

Flavour Physics Journal Paper

We study the effects of models with a warped extra dimension on rare charm decays. While the new degrees of freedom in these models are bounded above a few TeV, they can leave signatures in rare charm decays with their tiny Standard Model background. We look at several channels with leptons in the final state along with several asymmetries of both kinematical and dynamical nature. Charge-Parity-Time invariance is "usable" for analyzing the impacts of new dynamics in D meson decays and in particular, rare decays of charm mesons.

13 October 2012

On CP Asymmetries in Two-, Three- and Four-Body $D$ Decays

JHEP 1203 (2012) 021

Flavour Physics Journal Paper I. I. Bigi and A. Paul

On CP Asymmetries in Two-, Three- and Four-Body $D$ Decays

I. I. Bigi and A. Paul

JHEP 1203 (2012) 021

Flavour Physics Journal Paper

Indirect and direct CP violations have been established in $K_L$ and $B_d$ decays. They have been found in two-body decay channels -- with the exception of $K_L \to pi^+ pi^- e^+ e^-$ transitions. Evidence for direct CP asymmetry has just appeared in LHCb data on $A_{CP}(D^0 to K^+ K^-) - A_{CP}(D^0 to pi^+ pi^-)$ with 3.5 sigma significance. Manifestations of New Dynamics (ND) can appear in CP asymmetries just below experimental bounds. We discuss $D^{\pm}_{(s)}$, $D^0/\bar D^0$ and $D_L/D_S$ transitions to 2-, 3- and 4-body final states with a comment on predictions for inclusive vs. exclusive CP asymmetries. In particular we discuss T asymmetries in $D \to h_1 h_2 l^+ l^-$ in analogy with $K_L \to pi^+ pi^- e^+ e^-$ transitions due to interference between M1, internal bremsstrahlung and possible E1 amplitudes. Such an effect depends on the strength of CP violation originating from the ND -- as discussed here for Little Higgs Models with T parity and non-minimal Higgs sectors -- but also in the interferences between these amplitudes even in the Standard Model (SM). More general lessons can be learnt for T asymmetries in non-leptonic $D$ decays like $D \to h_1h_2 h_3 h_4$. Such manifestations of ND can be tested at LHCb and other Super-Flavour Factories like the projects at KEK near Tokyo and at Tor Vergata/Frascati near Rome.

29 March 2011

Conclusions from CDF Results on CP Violation in $D^0 \to \pi^+\pi^-$, $K^+K^-$ and Future Tasks

JHEP 1106 (2011) 089

Flavour Physics Journal Paper I. I. Bigi, A. Paul and S, Recksiegel

Conclusions from CDF Results on CP Violation in $D^0 \to \pi^+\pi^-$, $K^+K^-$ and Future Tasks

I. I. Bigi, A. Paul and S, Recksiegel

JHEP 1106 (2011) 089

Flavour Physics Journal Paper

Within the Standard Model (SM) one predicts both direct and indirect CP violation in $D^0 \to \pi^+\pi^-$, $K^+K^-$ transitions, although the effects are tiny: Indirect CP asymmetry cannot exceed $O(10^{-4})$, probably even $O(10^{-5})$ direct effects are estimated at not larger than $10^{-4}$. At $B$ factories direct and indirect asymmetries have been studied with $\tau_{D^0} \sim 1$ no CP asymmetry was found with an upper bound of about 1%. CDF has shown intriguing data on CP violation in $D^0 \to \pi^+\pi^-$ $[K^+K^-]$ with $\tau_{D^0} \sim 2.4 [2.65]$. Also, CDF has not seen any CP violation. For direct CP asymmetry, CDF has a sensitivity similar to the combination of the $B$ factories, yet for indirect CP violation it yields a significantly smaller sensitivity of $a_{cp}^{ind}=(-0.01 \pm 0.06_{stat} \pm 0.05_{syst})\%$ due to it being based on longer decay times. New Physics models (NP) like Little Higgs Models with T-Parity (LHT) can produce an indirect CP asymmetry up to 1% CDF's findings thus cover the upper range of realistic NP predictions ~ 0.1 - 1%. One hopes that LHCb and a Super-Flavour Factory will probe the lower range down to ~ 0.01%. Such non-ad-hoc NP like LHT cannot enhance direct CP violation significantly over the SM level in $D^0 \to \pi^+\pi^-$, $K^+K^-$ and $D^{\pm} \to \pi^{\pm}K^+K^-$ transitions, but others might well do so.

31 January 2011

On $D\to X_u l^+ l^-$ within the Standard Model and Frameworks like the Littlest Higgs Model with T Parity

Phys. Rev. D83 (2011) 114006

Flavour Physics Journal Paper I. I. Bigi, A. Paul and S, Recksiegel

On $D\to X_u l^+ l^-$ within the Standard Model and Frameworks like the Littlest Higgs Model with T Parity

I. I. Bigi, A. Paul and S, Recksiegel

Phys. Rev. D83 (2011) 114006

Flavour Physics Journal Paper

The $D\to X_u l^+ l^-$ transitions -- branching ratios, forward-backward asymmetry $A^c_{FB}$, the CP asymmetry $A^c_{CP}$ and the CP asymmetry in the forward-backward asymmetry $A^{CP}_{FB}$ -- have two sources: for $D^{\pm}$ they represent a pure $\Delta C=1$ & $\Delta Q=0$ current interaction whereas neutral $D$ mesons can also communicate via their anti-hadron. Standard Model (SM) contributions to BR$(D\to X_u l^+ l^-)$ come primarily from long distance dynamics, which overshadow short distance contributions by several orders of magnitude; still they fall much below the present upper experimental bounds. Even the SM contributions to $A^c_{FB}$, $A^c_{CP}$ and $A^{CP}_{FB}$ are tiny, quite unlike in beauty hadrons. The branching ratios are hardly dented by contributions from the Littlest Higgs Models with T parity (LHT) even in the short distance regime, let alone in the SM long distances dynamics. Yet the asymmetries $A^c_{FB}$, $A^c_{CP}$ and $A^{CP}_{FB}$ in these New Physics models can be enhanced over SM predictions, as they arise purely from short distance dynamics; this can occur in particular for $A^c_{FB}$ and $A^{CP}_{FB}$ which get enhanced by orders of magnitudes. Even such enhancements hardly reach absolute sizes for observable experimental effects for $A^c_{FB}$ and $A^c_{CP}$. However LHT contributions to $A^{CP}_{FB}$ could be measured in experiments like the LHCb and the SuperB Collaboration. These results lead us to draw further conclusions on FCNCs within LHT-like models through some simple scaling arguments that encapsulate the essence of flavour dynamics in and beyond the Standard Model.

18 August 2010

$D^0 \to \gamma \gamma$ and $D^0 \to \mu^+ \mu^-$ Rates on an Unlikely Impact of the Littlest Higgs Model with T-Parity

Phys.Rev. D82 (2010) 094006

Flavour Physics Journal Paper I. I. Bigi, A. Paul and S, Recksiegel

On $D\to X_u l^+ l^-$ within the Standard Model and Frameworks like the Littlest Higgs Model with T Parity

I. I. Bigi, A. Paul and S, Recksiegel

Phys.Rev. D82 (2010) 094006

Flavour Physics Journal Paper

The decays $D^0 \to \gamma \gamma$, $mu^+ mu^-$ are highly suppressed in the Standard Model (SM) with the lion's share of the rate coming from long distance dynamics $D^0 \to mu^+ mu^-$ is driven predominantly by $D^0 \to \gamma \gamma \to mu^+ mu^-$. Their present experimental bounds are small, yet much larger than SM predictions. New Physics models like the Littlest Higgs models with T parity (LHT) can induce even large indirect CP violation in $D^0$ transitions. One would guess that LHT has a 'fighting chance' to affect these $D^0 \to \gamma \gamma$, $mu^+ mu^-$ rates in an observable way. We have found LHT contributions can be much larger than short distance SM amplitude by orders of magnitude. Yet those can barely compete with the long distance SM effects. If $D^0 \to \gamma \gamma$, $mu^+ mu^-$ modes are observed at greatly enhanced rates, LHT scenarios will not be candidates for generating such signals. LHT-like frameworks will not yield larger $D^0 \rightarrow \gamma \gamma/mu^+ mu^-$ rates as they are constrained by $B$ and $K$ rare decays.

.04

SKILLS

PROGRAMMING
Developer of several open source codes focused on scientific computing: $\texttt{HEPfit}$, $\texttt{BAT}$, etc.
LEVEL : ADVANCEDEXPERIENCE : 14 YEARS
FORTRANC/C++PythonPerlshell scriptingHTML/JS
Machine Learning & Artificial Intelligence
Adept at large scale data analysis, classifications and regressions
LEVEL : ADVANCEDEXPERIENCE : 3 YEARS
DNNLSTMBDTClusteringTensorFlowXGBoostsklearn
PARALLEL COMPUTING
Experienced in parallelizing code and working in large clusters
LEVEL : ADVANCEDEXPERIENCE : 8 YEARS
MPIOpenMP
FUNCTIONAL PROGRAMMING
Widely used several software packages for functional programming
LEVEL : ADVANCEDEXPERIENCE : 15 YEARS
MathematicaMatLabformR
ANALYTICAL METHODS
Highly trained and experienced in Statistical analyses and inferences.
LEVEL : EXPERTEXPERIENCE : 15 YEARS
Bayesian AnalysisMarkov Chain Monte CarloMultivariate Methods
GITHUB HISTORY
.05

GRANTS & AWARDS

RESEARCH AND DEVELOPMENT GRANTS

2020

VolkswagenStiftung, Corona Crisis and Beyond – Perspectives for Science, Scholarship and Society

Talisman: Intelligent Algorithms for COVID-19 mitigation casting virtual safety nets to protect and empower the society.

2020

DESY Stategy Fund (Grant for COVID-19 Research)

CoVis: empowering health decisions, delivered by intelligent algorithms to contain COVID-19.

2012

Fund for GPS Summer Conferences

Raised Funding for the GPS Summer Conferences, 2012 for which I was a founding organizer.

2011

Notebaert Prof. Dev. Fund (II)

Grant for professional development from the Graduate School, University of Notre Dame du Lac.

2011

Notebaert Prof. Dev. Fund (I)

Grant for professional development from the Graduate School, University of Notre Dame du Lac.

2011

Joseph F. Downes Memorial Award,

Fellowship awarded for summer support for research from the Graduate School, Univeristy of Notre Dame du Lac.

2010

W. & L. Stavropoulos Fellowship

Fellowship awarded for summer support for research from the Graduate School, Univeristy of Notre Dame du Lac.

2009

Reilly Fellowship

Fellowship awarded for summer support for research from the Graduate School, Univeristy of Notre Dame du Lac.

2005

CSIR Junior Research Fellowship

Junior and Senior Research grant awarded by the Center for Scientific and Industrial Research, Govt. of India.

2003-2005

Research Fellowship

Junior Research grant awarded by the S N Bose National Center for Basic Sciences.

AWARDS

2020

MIT "Beat the Pandemic I" Hackathon Winning Team

CoVis: Empowering Decisions, Delivered by AI

2020

MIT "Beat the Pandemic II" Hackathon Winning Team

CoVis: Empowering Decisions, Delivered by AI

2012

Research and Dissertation Award

Awarded the Best Thesis award by the Department of Physics, University of Notre Dame du Lac.

2010

Kaneb Outstanding Graduate Teaching Assistant Award

Awarded for outstanding teaching records by the Kaneb Center, University of Notre Dame du Lac.

.06

TEACHING

  • TEACHING EXPERIENCE
  • 2019

    INSTRUCTOR

    Berlin QFT Master Class

    Hands-On Sessions on Electroweak Symmetry Breaking.
  • 2014

    INSTRUCTOR

    Lectures on CP Violation

    Topical lectures at the University of Notre Dame du Lac.
  • 2006
    2010

    TUTOR

    ACADEMIC SERVICES FOR STUDENT ATHLETES

    Taught Physics and Mathematics to the athletes in the University of Notre Dame du Lac.
  • 2006
    20011

    INSTRUCTOR

    FORTRAN FOR REU STUDENTS

    Designed and taught classes on FORTRAN at the University of Notre Dame du Lac.
  • 2006
    20011

    TEACHING ASSISTANT

    UNIVERSITY OF NOTRE DAME DU LAC

    Recipient of Kaneb Outstanding Graduate TA Award Graduate Courses: Classical Mechanics, Special and General relativity, Quantum Field Theory I, Quantum Mechanics, Particle Physics, Atomic Physics, Statistical Mechanics.
  • THESES SUPERVISION
  • 2015

    CLAUDIO FABIANI

    MS Thesis

    The decays of $B_{d,s}$ in the Standard Model.
  • 2014

    MARCO FEDELE

    MS Thesis

    Study of $B\to K^{*}\ell^+\ell^-$ decays in the Standard Model and Beyond.
.07

CONTACT

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