Trends in Astroparticle and Particle Physics

Sep 25, 2024, 7:30 AM → Sep 27, 2024, 5:30 PM Asia/Kolkata

Ramanujan Auditorium (IMSc Chennai)

Manjari Bagchi (The Institute of Mathematical Sceinces), Shankha Banerjee (The Institute of Mathematical Sciences, Chennai), Indumathi D (IMSc Chennai), Shrihari Gopalakrishna (IMSc Chennai), Dhiraj Hazra (IMSc Chennai), Padmanath M (Reader), Ravindran V (IMSc Chennai)

Trends in Astroparticle and Particle Physics (TAPP) is a three-day annual event jointly organized by the High Energy Physics and Astronomy-Cosmology groups at the Institute of Mathematical Sciences, Chennai. The purpose of this workshop is to discuss various recent developments in the fields of astro-particle and particle physics and the implications from experiments in astro-particle physics and cosmology. The format will include invited talks from leading physicists on various aspects of theory and experiment, broadly coming under the scope of Standard Model physics and beyond, along with opportunities for younger researchers to showcase their work in short talks.

This is the first edition of this event scheduled to be held from 25 to 27 September, 2024. The workshop is dedicated in memory of the late Prof. G. Rajasekaran, who was instrumental in shaping the high energy physics group at IMSc. The opening session of this event is planned to commemorate his contributions to science and to IMSc. 

Participation is open, although moderated, to others in the field, with special consideration for PhD students and post-doctoral researchers from Institutions across India. Highly motivated students pursuing masters degrees in Institutes in Chennai are also welcome to participate. Interested persons may register for participation and arrange for a reference letter on their behalf to be sent to tapp@imsc.res.in, clearly mentioning the name of the applicant in the subject header. A few of the selected participants who have submitted abstracts will have an opportunity to present their work in short talks in suitably organised sessions.

Registration Deadline: 31-July-2024

Note that as we have only a limited slots available for contributed talks, we might need to be selective.

Although the number of participants we can host is higher than the number of contributed talks, we might need to be selective for participants also in case of overwhelmingly large registrations.

The list of selected contributed talks and the list of participants will be published in this site.

 

List of confirmed speakers: 

Special lecture:

 M. V. N. Murthy (Prof. G. Rajasekaran: a life in science)

Experiment (alphabetical):

  Jim Libby, Rameez Md, Pratik Majumdar, Kajari Mazumdar

Theory (alphabetical):

Balasubramanian Ananthanarayan, Basudeb Dasgupta, Srubabati Goswami, Rick Sandeepan Gupta, Ranjan Laha, Ritam Mallick, Satyanarayan Mukhopadhyay, Sayantan Sharma, Anurag Tripathi, Sudhir Vempati

 

Live streaming:

YouTube channel: https://youtube.com/@matsciencechannel?si=aAW6OsR3RwVdNXXO

Zoom link: https://zoom.us/j/98048339163

Zoom meeting ID: 980 4833 9163

Zoom passcode: 684048

 

 

TAPP2024_Circular.pdf

TimeTable_allDays_TAPP2024.pdf

Workshop Poster

YouTube Channel streaming

Zoom link (PC: 684048)

Wednesday, September 25

9:00 AM → 9:30 AM Registration

9:30 AM → 11:00 AM Talks

Convener: Chair: V Ravindran (IMSc Chennai)

9:30 AM Rajaji- An Inward bound Journey

For almost six decades, Guruswamy Rajasekaran, fondly called Rajaji, has been an inspiring and leading member of the Physics community of India. In this talk we follow his refreshingly lively and honest career, recalling his contributions to Research. Teaching , Institution building, and public outreach.

Speaker: Mundur V N Murthy (The Institute of Mathematical Sciences, Chennai (Retired))

Murthy_tapp2024.pdf

10:15 AM Are Fractals Behind Flavor Mixing of the SM?

In the Standard Model of particle physics, each generation of fermion is replicated in all quantum numbers but with a higher mass in the next generation. Three chiral generations have been found so far. Using the replication property as an inspiration we look for fractal geometries to be behind the SM flavor mixing. A realistic model based on Sierpinski geometry on a deconstruction model (fractal dimension) is put forward.

Speaker: Aadarsh Singh (IISc Bangalore)

aadarsh_tapp2024.pdf

10:30 AM The role of large collider detectors in distinguishing astrophysical neutrinos from anti-neutrinos and its implications

--NA--

Speaker: Satyanarayan Mukhopadhyay (IACS Kolkata)

SMukhopadhyay_tapp2024.pdf

11:00 AM → 11:30 AM Coffee Break

11:30 AM → 1:00 PM Talks

Convener: Chair: Rahul Sinha (IMSc Chennai)

11:30 AM Feynman Integrals and Hypergeometric Functions: Recent Results and Mathematical Implementations

Hypergeometric function theory and Feynman Integral calculus go hand in hand. A series of recent investigations that culminated in the construction of several Mathematica packages that are based on Mellin-Barnes techniques, Method of Regions, hypergeometric function theory, etc., is reviewed in this talk to encourage the community to explore the use of these packages. The talk will be easily accessible to early Ph. D. students in elementary particle physics and field theory. He mentored a large number of young faculty members in many institutions often collaborating with them in their formative years.

Speaker: Balasubramanian Ananthanarayan

anant_tapp2024.pdf

12:00 PM Jet Substructure Methods for Polarization Measurement of Boosted Hadronic W Bosons

In this work, we introduce a novel technique for measuring the longitudinal and transverse polarization fractions of boosted hadronic $W$ boson decays. We propose a jet substructure observable, $p_\theta$, derived from subjet energies, serving as a proxy for the $W$ boson's parton-level decay polar angle in its rest-frame. This observable is sensitive to $W$ boson polarization and offers lower reconstruction errors than existing proxies, especially for highly boosted $W$ bosons. We demonstrate the effectiveness of our method using vector boson scattering processes at the High Luminosity LHC. With 10 ab$^{-1}$ of data, our technique achieves a 20% error in measuring the transverse $W$ polarization fraction. While detecting longitudinal polarization consistent with the Standard Model at the 2-$\sigma$ level remains challenging, our method could identify enhancements in beyond Standard Model scenarios, aiding in unitarity restoration studies.

Speaker: Songshaptak De (Institute of Physics Bhubaneswar)

SDe_tapp2024.pdf

1:00 PM → 2:30 PM Lunch break

2:30 PM → 4:00 PM Talks

Convener: Chair: Mundur V N Murthy (IMSc Chennai)

2:30 PM The strange case twin neutron stars and its merger

The presentation will be about the occurrence of twin neutron stars due to first order phase transition. I will also discuss its strange behaviors and the observational aspects of twin binary mergers in Gravitational wave signals.

Speaker: Ritam Mallick (IISER Bhopal)

Mallick_tapp2024.pdf

Mallick_tapp2024.pptx

3:00 PM Neutrino Flavor and Anderson Localisation

Random couplings can be generated in low energy theories in certain classes of UV theories like String landscape, dark matter models with high symmetries etc. Low energy clockwork like models can be generated with random mass parameters. It has been shown that such models give rise to Anderson like localisation for all the modes of the clockwork chain. It has been studied for lightness of neutrino masses. We show that for most geometries of Anderson location happens with non-local and local mass terms. A straight frorward extension can be made for three flavors but the limit of strong localiation always has anarchial mixing angles. However there are models with low disorder and weak localisation which can lead to respective mixing angles along with the scale.

Speaker: Sudhir Vempati [ONLINE] (IISc Bangalore)

Sudhir_tapp2024.pdf

3:30 PM Holographic Dark Energy: Possibility of negative dark energy at $z\gtrsim 2$

In holographic dark energy (HDE) models, infrared cut-offs with derivatives of the Hubble parameter, such as the Granda -- Oliveros cut-off, offer a coherent explanation for late-time acceleration while ensuring causal consistency. We show that such HDE will inevitably mimic the dominant energy forms unless we forcefully calibrate the free parameters. This feature reveals the dependency between the model's ability to explain the late-time acceleration and the integration constant, highlighting that one cannot arbitrarily set this constant to zero. We see that the origins of HDE and the Friedmann equations from the first law of horizon thermodynamics offer a natural explanation for this behaviour. Thus, the holographic principle naturally extends to all energy components, diverging from the prevalent notion in HDE models. The model also allows dark energy to transit from an early negative energy to a present positive value, with a singular dark energy equation of state parameter, which can relax the tension in the BAO Lyman-$\alpha$ observations. Furthermore, we present observational constraints utilizing Pantheon$^+$, OHD, CMB Shift parameter, QSO and BAO data, indicating the presence of early negative energy as an unavoidable consequence. Upon using the SH0ES prior, we see that the model accounts for the Hubble parameter at the cost of affecting the matter density while simultaneously relaxing the tensions in BAO Lyman-$\alpha$ observations and the age estimations. This study also underscores notable features stemming from the comprehensive utilization of the covariance matrix within cosmic chronometers, BAO and CMB distance prior and clarifies the implications of negative dark energy density derived from the high redshift Pantheon$^+$ sample. Additionally, we provide a brief overview of the theoretical framework surrounding linear perturbation within the $w$GOHDE model. Abstract Based on (Manoharan, M.T. Insights on Granda–Oliveros holographic dark energy: possibility of negative dark energy at $z\gtrsim 2$. Eur. Phys. J. C 84, 552 (2024). https://doi.org/10.1140/epjc/s10052-024-12926-z)

Speaker: Manosh T. Manoharan (Department of Physics, Cochin University of Science and Technology, Kochi - 682022, India.)

Manosh_tapp2024.pdf

3:45 PM Prospects of Dynamic Radius Jet Clustering Algorithm at the LHC

The emergence of jets, bunches of collimated hadrons, in high-energy colliders is a prevalent phenomenon. In the current LHC context, along with traditional narrow QCD jets, the study of fat jets, which may appear as a result of the decay of a heavy particle, has become an essential part of collider studies. Current jet clustering algorithms, namely kt-type sequential recombination algorithms, use fixed radius parameters for the formation of jets from the hadrons of an event in a collider. The appearance of differently-sized jets in a single event from such algorithms is, therefore, impossible to achieve. In our work, we made an attempt to form differently-sized jets via the dynamic radius chosen during the evolution of each jet. Instead of keeping the constant radius parameter of the standard kt-type sequential recombination algorithms, we allowed the radius to vary dynamically based on the local kinematics and distribution in the eta-phi plane around each evolving jet. In this talk, I will discuss our methodology of the dynamic radius jet algorithm. I will then present the usefulness of the algorithm at the 13 TeV LHC through some example processes from SM and BSM scenarios.

Speaker: Tousik Samui (The Institute of Mathematical Sciences)

Tousik_tapp2024.pdf

4:00 PM → 4:30 PM Coffee break

4:30 PM → 5:30 PM Poster

4:30 PM Application of thermal field theory to dark matter annihilation cross section

Speaker: Prabhat Butola (IMSc Chennai)

prabhat_tapp2024.pdf

4:30 PM Constraints on decaying dark matter and anomalous kolar events

Speaker: Thiru Senthil R (IMSc Chennai)

Senthil_tapp2024.pdf

4:30 PM Dibaryons: Insights from the Heavy Quark Sector

Speaker: Navdeep Singh Dhindsa (IMSc Chennai)

Navdeep_tapp2024.pdf

4:30 PM Indirect detection of dark matter annihilating into long-lived mediators from dwarf spheroidal galaxies

Speaker: Aman Gupta (IIT Roorkee)

aman_tapp2024.pdf

4:30 PM Lattice QCD study of doubly heavy bottom tetraquarks

Speaker: Bhabani Sankar Tripathy (The institute of Mathematical Sciences,Chennai)

Bhabani_tapp2024.pdf

4:30 PM NNLO QCD corrections to semi-inclusive DIS

Speaker: Saurav Goyal (The Institute of Mathematical Sciences, Chennai)

Saurav_tapp2024.pdf

4:30 PM ORIGIN OF COSMIC RAYS

Speaker: HIBA P (PONDICHERRY UNIVERSITY)

Thursday, September 26

9:30 AM → 11:00 AM Talks

Convener: Chair: T R Govindarajan (IMSc Chennai)

9:30 AM Belle II highlights: flavour physics and more

This talk will review the current results from Belle II. These results will cover the core B physics programme related to measurements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. In addition, the impact of the experiment away from B physics is also showcased, with the presentation of recent results related to the tau lepton, charm physics, dark sector and hadronic physics.
The talk concludes with the status and prospects for the experiment and SuperKEKB collider.

Speaker: Jim Libby (IIT Madras)

Jim_tapp2024.pdf

10:15 AM Hunting Primordial Black Hole Dark Matter in Lyman-alpha forest

The question that what constitutes Dark Matter (DM) is one of the most pressing ones in contemporary physics, and one that has not been answered to any degree so far. Primordial Black Holes (PBHs) are one of the most well-motivated dark matter candidates. PBHs which are light enough that the Hawking radiation is substantial have been constrained by either the non-detection of the radiation itself, or by the non-observation of any measurable effects of the radiation on astrophysical and cosmological observables. In this work, we constrain the existence of such PBHs by the effect their Hawking radiation would have had on the temperature of the intergalactic medium (IGM). We use the latest deductions of IGM’s temperature from the Lyman-alpha forest observations. We put constraints on the fraction of dark matter that PBHs can constitute with masses in the range 5 x 10^15 g – 10^17 g, separately for spinning and non-spinning black holes. We derive the constraints by dealing with the heating effects of the astrophysical reionization of the IGM in two ways. In one way, we completely neglect this heating due to astrophysical sources, thus giving us relatively weak constraints, but which are completely robust to the reionization history of the universe. In the second way, we use some modelling of the ionization and temperature history and use them to derive more stringent constraints. We find that for PBHs of mass 10^16 g, the current measurements can constrain the PBH-density to be less than 0.1% of the total dark matter density, both for spinning and non-spinning black holes. Thus, we find that these constraints from the Lyman-alpha measurements are competitive, and hence provide a new observable to probe the nature of dark matter.

Speaker: Abhijeet Singh (IISc)

Abhijeet_tapp2024.pdf

10:30 AM Understanding the role of chiral symmetry in the QCD phase diagram

The strong interactions account for the origin of an overwhelming fraction of the visible matter in the universe. Strongly interacting matter described by quantum chromodynamics (QCD) has a very rich phase diagram in terms of temperature and net baryon-density. Lattice QCD has provided exciting new results from first-principles but still much of it remains unknown. Unraveling the QCD phase diagram is one of the goals of theoretical physics as it accounts for the rich phenomena at myriad length scales--from tiny droplets formed in heavy-ion colliders as well as in the core of neutron stars. In this talk I will focus on aspects of chiral symmetry and its effects on the QCD phase diagram from lattice studies.

Speaker: Sayantan Sharma

ssharma_tapp24.pdf

11:00 AM → 11:30 AM Coffee break

11:30 AM → 1:00 PM Talks

Convener: Chair: Nita Sinha (IMSc Chennai)

11:30 AM The Road to a Deuterated Scintillator-Based Detector

Most neutrino detectors only detect electron-antineutrinos. However, in many situations it would be immensely more useful to detect all neutrino flavors --- e.g., how SNO neutral current data helped solve the solar neutrino problem. I will present some not-fully-ripe ideas towards building such an all-flavor-sensitive scintillator-based detector, leveraging India's unique strength in production of deuterated materials.

Speaker: Basudeb Dasgupta (TIFR Mumbai)

Basu_tapp2024.pdf

12:00 PM Exotic Tccus tetraquark from numerical simulations of QCD

The recent discovery of the exotic Tcc tetraquark by the LHCb collaboration has garnered significant interest in the particle physics community. Building on this discovery, our research investigates the potential existence of another exotic tetraquark, Tccus, which could be within the reach of LHCb, if it exists. Using lattice QCD, a first-principles approach, we simulate scattering of charm D and charm-strange Ds mesons. Finite volume energy spectra, determined using variational procedures, are utilized to extract the coupled channel DDs-DsD scattering amplitudes. Pole singularities in the resultant amplitudes across the complex energy plane are extracted and studied in conjunction with the known hadronic features in the experimental cross sections and/or with potentially yet-to-be-discovered tetraquark candidates.

Speaker: Tanishk Shrimal (IMSc Chennai)

Doubly charm tetraquark

Tanishk_tapp2024.pdf

12:15 PM LHC: always exciting

The physics harvest at the LHC is always rich and interesting. This talk will highlight only a few recent results from the experiments to showcase the breadth of physics scope of the LHC.

Speaker: Kajari Mazumdar (TIFR Mumbai)

Kajari_tapp2024_updated.pdf

1:00 PM → 2:30 PM Lunch break

2:30 PM → 3:30 PM Talks

Convener: Chair: Kajari Mazumdar

2:30 PM Cosmological selection of a small weak scale from a large vacuum energy: a minimal approach

We present a minimal cosmological solution to the hierarchy problem. Our model consists of a light pseudoscalar and an extra Higgs doublet in addition to the field content of the Standard Model. We consider a landscape of vacua with varying values of the electroweak vacuum expectation value (VEV). The vacuum energy in our model peaks in a region of the landscape where the electroweak VEV is small. During inflation such regions of the landscape with maximal vacuum energy, dominate the universe in volume,The pseudoscalar potential in our model is that of a completely generic pseudogoldstone boson −not requiring the clockwork mechanism–and its field value never exceeds its decay constant or the Planck scale. Our mechanism is robust to the variation of other model parameters in the landscape along with the electroweak VEV. It also predicts a precise and falsifiable relationship between the masses and couplings of the different Higgs boson mass-eigenstates. Moreover, the pseudoscalar in our model can account for the observed dark matter relic density.

Speaker: Rick Sandeepan Gupta (TIFR Mumbai)

Rick_tapp2024.pdf

3:00 PM Primordial power spectrum in light of JWST observations of high redshift galaxies

Early data releases of JWST have revealed several high redshift massive galaxy candidates by photometry, and some of them have been confirmed spectroscopically. We study their implications on the primordial power spectrum. In the first part, we use the CEERS photometric survey data, along with respective spectroscopic updates, to compute the cumulative comoving stellar mass density. We find that a very high star formation efficiency (unlikely in various theoretical scenarios) is required to explain these observations within Lambda cold dark matter (ΛCDM) cosmology. We show that the tension can be eased if the primordial power spectrum has a blue tilt. In the second part, we study spectroscopically confirmed galaxies reported in the JADES survey to investigate their implications on a red-tilted primordial power spectrum. We estimate the star formation efficiency from an earlier observation at similar redshift by {\it Spitzer}, and find that the star formation efficiency is an order of magnitude smaller than required to explain the CEERS photometric observations mentioned earlier. Using the estimated star formation efficiency, we find the strongest constraints on the red tilt of the power spectrum over some scales. Our study shows that JWST will be an excellent probe of the power spectrum and can lead to novel discoveries.

Speaker: Ranjan Laha (IISc Bangalore)

RLaha_tapp2024.pdf

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:15 PM Talks

Convener: Chair: Kajari Mazumdar

4:00 PM New Physics with $N_{\rm eff}$ in the CMB

The precise measurement of $N_{\rm eff}$ at the time of cosmic microwave background (CMB) formation by Planck (2018) can be used to understand the new fundamental interactions, in particular those involving light mediators. In this talk, I will discuss the impact of light gauge bosons (order of MeV) originating from various types of $U(1)_X$​ on the $N_{\rm eff}$. In the low-mass region, the bound on $N_{\rm eff}$​ at CMB is more stringent than current experimental constraints.

Speaker: Purusottam Ghosh (IMSc Chennai)

TAPP_IMSc_PurusottamGhosh.pdf

4:15 PM Is the CP violation observed in D decays a signal of new Physics

The observation of CP violation in $D\to K^+K^-$ and $D\to \pi^+\pi^-$ has raised a debate whether the observed CP asymmetries can be regarded as a signal of physics beyond the standard model (SM). We show that the measured observables for $D\to \pi\pi$ unambiguously imply a very large penguin contribution that is greater than $5\%$ of the amplitude for $D^+\to\pi^+ \pi^0$ at a significance greater than $3.6 \sigma$. We present arguments based only on unitarity of re-scattering amplitudes to show that large penguin contribution cannot arise from re-scattering and indicate physics beyond the SM. In a model independent approach, we show how a very small contribution from physics beyond the SM with a weak phase alleviates the problem.

Speaker: Rahul Sinha (IMSc Chennai)

RSinha_tapp2024.pdf

4:45 PM Patterns in Scattering Amplitudes

Scattering amplitudes involving multiple partons are plagued with infrared singularities. The soft singularities of the amplitudes are captured by the soft function which is defined as the vacuum expectation value of Wilson line correlators. Renormalization properties of soft function allows us to write it as an exponential of the finite soft anomalous dimension. An efficient way to study the soft function is through a set of Feynman diagrams known as Cwebs (webs). In this talk I will discuss the progress that has been made by our group in the last couple of years in understanding the structure and the building blocks of Cwebs.

Speaker: Anurag Tripathi (IIT Hyderabad)

ATripathi_tapp2024.pdf

5:30 PM → 6:00 PM High Tea

6:00 PM → 7:30 PM Special Coloquium: TBA

Convener: Chair: D Indumati

6:00 PM The history of Higgs boson

Speaker: Gautam Bhattacharyya (SINP Kolkata)

Higgs_history.pdf

Friday, September 27

9:30 AM → 11:00 AM Talks

Convener: Chair: Srubabati Goswami (PRL)

9:30 AM Multimessenger Astroparticle Physics using photons and neutrinos

--NA--

Speaker: Pratik Majumdar (SINP Kolkata)

Multimessenger_IMSc_2024.pdf

10:15 AM Dark matter cooling during early-matter domination boosts sub-earth halo formation

The existence of an early matter-dominated epoch prior to the big bang nucleosynthesis may lead to a scenario where the thermal dark matter starts to cool faster than the plasma before the onset of reheating. In the standard radiation-dominated epoch, the thermal dark matter free-streams after it decouples both chemically and kinetically from the plasma. In presence of an early matter-dominated epoch, the chemical decoupling of the dark matter may be followed by a partial kinetic decoupling prior to the reheating, depending upon the contribution of different partial wave amplitudes in the elastic scattering of the dark matter. We show that the s-wave scattering is sufficient to keep the dark matter partially decouple from the plasma, provided the entropy injection during the reheating epoch depends on the bath temperature, while p-wave scattering will lead to a full decoupling in such cosmological backdrop. Decoupling during the early matter domination leads to an additional amount of cooling before the commencement of radiation dominated universe, which reduces the free-streaming horizon of dark matter compared to usual radiation-dominated cosmology. The enhanced matter perturbations for scales entering the horizon before, or during reheating, together with the reduced free-steaming horizon of dark matter increases the number density of sub-earth mass halos. As a result the annihilation signatures of the dark matter in the galactic centres may receive a significant boosts, providing an intrguing probe to differentiate non-standard cosmological epoch prior to BBN. Fo illustration we examine two simple dark matter models, one featuring a scalar dark matter with s-wave scattering and the other a fermion dark matter with p-wave scattering.

Speaker: Avik Banerjee (TIFR)

ABanerjee_tapp2024.pdf

10:30 AM Long-lived particles: unconventional signatures in collider experiments

--NA--

Speaker: Biplob Bhattacherjee

Biplob_tapp2024.pdf

11:00 AM → 11:30 AM Coffee break

11:30 AM → 1:00 PM Talks

Convener: Chair: D. Indumathi

11:30 AM The curious case of the sterile neutrino

The framework of three-flavor neutrino oscillation is well-established from different experiments. However results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional light neutrino state characterized by a mass-squared difference of approximately 1  eV^2. The new neutrino state is devoid of all Standard Model interactions, commonly referred to as a “sterile” state. This talk will summarize the current status in the search of the eV scale sterile neutrino and future experiments that can possibly resolve the issue. In addition the possibility of lighter sterile neutrinos and constraining the mass spectra in presence of such species from cosmology, neutrinoless double beta decay and measurement of absolute neutrino mass from beta decay experiments will also be discussed.

Speaker: Srubabati Goswami (PRL Ahmedabad)

sterillle_trend.pdf

12:00 PM Surface magnetic field of neutron stars

Unlike X-ray pulsars, the isolated radio pulsars have a rather ‘quiet’ surface activity where the key forces are the strong surface gravity and the surface magnetic fields. The strong surface magnetic field leads to pair production and subsequent generation of the electron positron plasma and finally the radio beam and other emissions. The observed pulse patterns of the radio pulsars thus depend on the emission mechanism taking place at the polar caps that are highly guided by these surface magnetic field. The surface magnetic field on the other hand depends on the transport properties of a rapidly varying matter of the neutron star crust. We study the decay of the magnetic field of a neutron star assuming the magnetic field of the star is mostly located in the outer crust. We further study the effect of radial oscillation on the surface magnetic field and their relevance to observational features.

Speaker: Subharthi Ray (Astrophysics Research Centre, University of KwaZulu-Natal, Durban)

SRay_tapp2024.pdf

12:30 PM Positivity Bounds on HEFT Operators

The analytic structure and the unitarity of S-matrix enforces non-trivial constraints (known as positivity bounds) on the space of Wilson coefficients of an EFT. The simplest bounds are derived by setting the coefficient of $s^2$ in the amplitude of $2 \to 2$ elastic scattering process in the forward limit, to zero. Meanwhile stronger bounds can be extracted in some occasions by exploiting the positive-definite structure of the $2 \to 2$ scattering amplitude. In this talk, I will discuss how we employ these methods to constrain Wilson coefficients of the 15 $\mathcal{O}(p^4)$ operators of the HEFT Lagrangian. We compare positivity bounds that we derive, with the recent experimental bounds on the 5 QGC operators and show that positivity bounds rule out most of the parameter space. Only $\sim \mathcal{O}(10\%)$ of the total parameter space is consistent with these positivity bounds.

Speaker: Susobhan Chattopadhyay (TIFR Mumbai)

TAPP_Susobhan_Positivity bounds on HEFT operators.pdf

12:45 PM Exploring the Impact of Extra Dimensions on the Equation of State and the Structure of Neutron Stars

In this work, we explore the impact of higher dimensional spacetime on the stellar structure and thermodynamic properties of neutron stars. Utilizing the density-dependent relativistic hadron field theory, we introduce modifications to incorporate the influence of higher dimensionality. Our methodology involves solving the essential stellar structure equations in the $D$-dimensional spacetime ($D \geq 4$), starting with the modification of the Einstein-Hilbert action, derivation of the Einstein field equation in the $D$-dimension, and application of the resulting exterior Schwarzschild spacetime metric for the $D$-dimension. Our findings indicate that with increasing dimensions, the central density $\rho_{c} G_D$ and the central pressure $p_c G_D$ required to achieve the maximum mass for neutron stars progressively increase, resulting in stiffer neutron matter. Incremental dimensionality also results in a gradual increase in the maximum mass attained, limited to our study between $D=4$ and $D=6$, as no maximum mass value is obtained for $D>6$. We consistently observe the criteria $dM/d\rho_c>0$ fulfilled up to the maximum mass point, supported by stability analysis against infinitesimal radial pulsations. The validity of our solution is confirmed through the causality condition, ensuring that the matter sound speed remains within the speed of light for all cases. Additionally, our examination indicates that the total mass-to-radius ratio for all discussed $D$-dimensional cases comfortably resides within the modified Buchdahl limit. Furthermore, by projecting the compactified $D$-dimensional maximum neutron star mass into the four dimensions, our study suggests that the mass of the secondary object observed in GW190814 can be explained.

Speaker: DEBABRATA DEB

DDeb_tapp2024.pdf

1:00 PM → 3:00 PM Lunch break

3:00 PM → 3:45 PM Talks

Convener: Chair: Manjari Bagchi

3:00 PM Anisotropy and the missing rest frame of the Universe falsify standard dark cosmology

--NA--

Speaker: Mohamed Rameez (TIFR Mumbai)

3:45 PM → 4:15 PM Coffee break