arXiv subjects

Behnam Mohammadi

Publications and source records attributed to Behnam Mohammadi.

13 recordsLinked to original sources

arXiv2026

Amplitude analysis and branching fraction calculations of $B_c$ meson decays into $B_sπ$, $DKπ$ and $D_sKK$ final state mesons

In this study, several newly observed decay modes of the $B_c^+$ meson of the form $B_c^+\rightarrow Dh^+h^-$, where $D$ denotes a charmed meson and $h^{\pm}$ represents a charged pion or kaon, have been investigated. The decay channels $B_c^+\rightarrow D^{+}K^+π^{-}$, $B_c^+\rightarrow D^{*+}K^+π^{-}$ and $B_c^+\rightarrow D_s^+K^+K^-$ were observed for the first time. The LHCb Collaboration has measured their branching fractions relative to the reference decay $B_c^+\rightarrow B_s^0π^+$, and reported experimental values including $\mathcal{R}^{\exp}(B_c^+\rightarrow D^{+}K^+π^{-})=(1.96\pm0.23\pm0.08\pm0.10)\times 10^{-3}$ , $\mathcal{R}^{\exp}(B_c^+\rightarrow D^{*+}K^+π^{-})=(3.67\pm0.55\pm0.24\pm0.20)\times10^{-3}$ and $\mathcal{R}^{\exp}(B_c^+\rightarrow D_s^+K^+K^{-})=(1.61\pm0.35\pm0.13\pm0.07)\times 10^{-3}$. In this regard, by performing precise calculations using the factorization approach, we have computed similar branching ratio values, including $\mathcal{R}(B_c^+\rightarrow D^{+}K^+π^{-})=(1.70\pm0.08)\times 10^{-3}$, $\mathcal{R}(B_c^+\rightarrow D^{*+}K^+π^{-})=(3.63\pm0.45)\times 10^{-3}$ and $\mathcal{R}(B_c^+\rightarrow D_s^+K^+K^{-})=(1.09\pm0.08)\times 10^{-3}$. The obtained theoretical results show good consistency with the recent experimental measurements reported by the LHCb collaboration, confirming the effectiveness of the factorization formalism in describing these $B_c^+$ decay modes.

hep-ph↗

arXiv2025

Pel, A Programming Language for Orchestrating AI Agents

The proliferation of Large Language Models (LLMs) has opened new frontiers in computing, yet controlling and orchestrating their capabilities beyond simple text generation remains a challenge. Current methods, such as function/tool calling and direct code generation, suffer from limitations in expressiveness, scalability, cost, security, and the ability to enforce fine-grained control. This paper introduces Pel, a novel programming language specifically designed to bridge this gap. Inspired by the strengths of Lisp, Elixir, Gleam, and Haskell, Pel provides a syntactically simple, homoiconic, and semantically rich platform for LLMs to express complex actions, control flow, and inter-agent communication safely and efficiently. Pel's design emphasizes a minimal, easily modifiable grammar suitable for constrained LLM generation, eliminating the need for complex sandboxing by enabling capability control at the syntax level. Key features include a powerful piping mechanism for linear composition, first-class closures enabling easy partial application and functional patterns, built-in support for natural language conditions evaluated by LLMs, and an advanced Read-Eval-Print-Loop (REPeL) with Common Lisp-style restarts and LLM-powered helper agents for automated error correction. Furthermore, Pel incorporates automatic parallelization of independent operations via static dependency analysis, crucial for performant agentic systems. We argue that Pel offers a more robust, secure, and expressive paradigm for LLM orchestration, paving the way for more sophisticated and reliable AI agentic frameworks.

cs.PL↗

arXiv2024

Explaining Large Language Models Decisions Using Shapley Values

The emergence of large language models (LLMs) has opened up exciting possibilities for simulating human behavior and cognitive processes, with potential applications in various domains, including marketing research and consumer behavior analysis. However, the validity of utilizing LLMs as stand-ins for human subjects remains uncertain due to glaring divergences that suggest fundamentally different underlying processes at play and the sensitivity of LLM responses to prompt variations. This paper presents a novel approach based on Shapley values from cooperative game theory to interpret LLM behavior and quantify the relative contribution of each prompt component to the model's output. Through two applications - a discrete choice experiment and an investigation of cognitive biases - we demonstrate how the Shapley value method can uncover what we term "token noise" effects, a phenomenon where LLM decisions are disproportionately influenced by tokens providing minimal informative content. This phenomenon raises concerns about the robustness and generalizability of insights obtained from LLMs in the context of human behavior simulation. Our model-agnostic approach extends its utility to proprietary LLMs, providing a valuable tool for practitioners and researchers to strategically optimize prompts and mitigate apparent cognitive biases. Our findings underscore the need for a more nuanced understanding of the factors driving LLM responses before relying on them as substitutes for human subjects in survey settings. We emphasize the importance of researchers reporting results conditioned on specific prompt templates and exercising caution when drawing parallels between human behavior and LLMs.

cs.CL↗

arXiv2024

Contributions of $ψ_{2}(3823)$ and $ψ(4040)$ charmonium in $B^+\rightarrow J/ψηK^+$ decay

Recently, a study on the $J/ψη$ mass spectrum from $B^+\rightarrow J/ψηK^+$ decays was reported by the LHCb detector. The results of this study are reported as a ratio of branching fractions as $F_{X}\equiv\frac{\mathcal{B}r(B^+\rightarrow XK^+)\times\mathcal{B}r(X\rightarrow J/ψη)}{\mathcal{B}r(B^+\rightarrow ψ(2S) K^+)\times\mathcal{B}r(ψ(2S)\rightarrow J/ψη)}$ for $X=ψ_2(3823),ψ(4040)$, which are $(5.95^{+3.38}_{-2.55})\times10^{-2}$ and $(40.60\pm11.20)\times10^{-2}$, respectively. Also, the products related to $B_{X}\equiv\mathcal{B}r(B^+\rightarrow XK^+)\times\mathcal{B}r(X\rightarrow J/ψη)$ branching fractions are $B_{ψ_2(3823)}=(1.25^{+0.71}_{-0.53}\pm0.04)\times10^{-6}$ and $B_{ψ(4040)}=(8.53\pm2.35\pm0.30)\times10^{-6}$. For the first time, we calculated this branching fraction using factorization. According to our calculations, $F_X$ to be $F_{ψ_{2}(3823)}=(6.55\pm1.88)\times10^{-2}$ and $F_{ψ(4040)}=(14.33\pm4.15)\times10^{-2}$ at $μ=m_b/2$. We have estimated $B_{ψ_{2}(3823)}=(0.26\pm0.05)\times10^{-6}$ at $μ=m_b/2$ and $B_{ψ(4040)}=(2.88\pm0.64)\times10^{-6}$ at $μ=2m_b$.

hep-ph↗

arXiv2024

Creativity Has Left the Chat: The Price of Debiasing Language Models

Large Language Models (LLMs) have revolutionized natural language processing but can exhibit biases and may generate toxic content. While alignment techniques like Reinforcement Learning from Human Feedback (RLHF) reduce these issues, their impact on creativity, defined as syntactic and semantic diversity, remains unexplored. We investigate the unintended consequences of RLHF on the creativity of LLMs through three experiments focusing on the Llama-2 series. Our findings reveal that aligned models exhibit lower entropy in token predictions, form distinct clusters in the embedding space, and gravitate towards "attractor states", indicating limited output diversity. Our findings have significant implications for marketers who rely on LLMs for creative tasks such as copywriting, ad creation, and customer persona generation. The trade-off between consistency and creativity in aligned models should be carefully considered when selecting the appropriate model for a given application. We also discuss the importance of prompt engineering in harnessing the creative potential of base models.

cs.CL↗

arXiv2024

Regulating eXplainable Artificial Intelligence (XAI) May Harm Consumers

Recent AI algorithms are black box models whose decisions are difficult to interpret. eXplainable AI (XAI) is a class of methods that seek to address lack of AI interpretability and trust by explaining to customers their AI decisions. The common wisdom is that regulating AI by mandating fully transparent XAI leads to greater social welfare. Our paper challenges this notion through a game theoretic model of a policy-maker who maximizes social welfare, firms in a duopoly competition that maximize profits, and heterogenous consumers. The results show that XAI regulation may be redundant. In fact, mandating fully transparent XAI may make firms and consumers worse off. This reveals a tradeoff between maximizing welfare and receiving explainable AI outputs. We extend the existing literature on method and substantive fronts, and we introduce and study the notion of XAI fairness, which may be impossible to guarantee even under mandatory XAI. Finally, the regulatory and managerial implications of our results for policy-makers and businesses are discussed, respectively.

cs.AI↗

arXiv2023

Analysis of $B^0_s\rightarrow χ_{c1}(3872)π^+π^-$ decay

Recently, the LHCb collaboration has analyzed the decay of $B_s^0\rightarrow χ_{c1}(3872)(\rightarrow J/ψπ^+ π^-) π^+ π^-$ and reported the ratio of the branching fractions to the $B_s^0\rightarrow ψ(2S)(\rightarrow J/ψπ^+π^-)π^+π^-$ decay. The results of this study have measured as a ratio of branching fractions as{\setlength\arraycolsep{.75pt} \begin{eqnarray} \mathcal{R}&=&\frac{\mathcal{B}r(B_s^0\rightarrowχ_{c1}(3872)π^+π^-)\times\mathcal{B}r(χ_{c1}(3872)\rightarrow J/ψπ^+π^-)}{\mathcal{B}r(B_s^0\rightarrowψ(2S)π^+π^-)\times\mathcal{B}r(ψ(2S)\rightarrow J/ψπ^+π^-)}\nonumber\\&=&(6.8\pm1.1\pm0.2)\times10^{-2},\nonumber \end{eqnarray}} and{\setlength\arraycolsep{.75pt} \begin{eqnarray} \mathcal{B_X}&=&\mathcal{B}r(B_s^0\rightarrowχ_{c1}(3872)π^+π^-)\times\mathcal{B}r(χ_{c1}(3872)\rightarrow J/ψπ^+π^-)\nonumber\\&=&(1.6\pm0.3\pm0.1\pm0.3)\times10^{-6}.\nonumber \end{eqnarray}} For the first time, we calculated this branching fraction using factorization. According to our calculations, ratio of branching fractions to be $\mathcal{R}=(4.38\pm1.36)\times10^{-2}$ at $μ=m_b/2$ and the products related to branching fractions have been estimated $\mathcal{B_X}=(1.08\pm0.62)\times10^{-6}$ at $μ=m_b$. The results are consistent with the experiment reported.

hep-ph↗

arXiv2023

Measurement of the Quasi-Two-Body B Decays

We study the contributions of the $B\rightarrow ψ(3770)K[ψ(3770)\rightarrow D\bar{D}]$, $B\rightarrow K^*(1410)π[K^*(1410)\rightarrow Kπ]$ and $B\rightarrow X(3872)K[X(3872)\rightarrow J/ψγ, ψ(2S)γ, D\bar{D}π, J/ψω, J/ψππ$ and $D\bar{D}^*π]$ quasi-two-body decays. There are no existing previous measurement of the three-body branching fractions for three final states of the $X(3872)\rightarrow J/ψγ$, $ψ(2S)γ$ and $D\bar{D}π$ but several quasi-two-body modes that can decay to this final state have been seen.

hep-ex↗

arXiv2023

Estimated of $CP$ violation in $B^0$ meson decays into $D^{*+}$ and $D^-$ mesons

The decay $B^0\rightarrow D^{*+}D^-$ is favorable mode for studying $CP$ violation in the interference between mixing and decay for $B^0$ and $\bar{B}^0$ mesons. The latest analysis of the $CP$ parameters has been performed by the LHCb collaboration values of $S_{D^*D}=-0.861\pm0.077\pm0.019$, $C_{D^*D}=-0.059\pm0.092\pm0.020$, $\triangle S_{D^*D}=0.019\pm0.075\pm0.012$, $\triangle C_{D^*D}=-0.031\pm0.092\pm0.016$, and $\mathcal{A}_{D^*D}^{CP}=0.008\pm0.014\pm0.006\pm0.003$. We have been estimated the parameters $S_{D^*D}$ and $C_{D^*D}$ of the $B^0\rightarrow D^{*+}D^-$ decay as $-0.709\pm0.024$ and $-0.051\pm0.004$. In the following, we have obtained the values of $\triangle S_{D^*D}=0.054\pm0.003$ and $\triangle C_{D^*D}=0.020\pm0.001$ and direct $CP$ violation of $0.008\pm0.001$. Also, we have calculated the branching ratio of $B^0\rightarrow D^{*+}D^-$ decay. The values obtained in this work are comparable with the corresponding experimental values.

hep-ph↗

arXiv2023

Study of $B^+_c$ decays to the $K^+K^-π^+$ final state by using $B^0_s$, $χ_{c0}$ and $D^0$ resonances and weak annihilation nonresonant topologys

In this research the weak decay of $B^+_c$ decays to the $K^+K^-π^+$ final state, which is observed by LHCb collaboration for the first time, is calculated in the quasi-two-body decays which takes into account the $B^0_s$, $χ_{c0}$ and $D^0$ resonances and weak annihilation nonresonant contributions. In this process, the $B^+_c$ meson decays first into $B^0_sπ^+$, $χ_{c0}π^+$ and $D^0π^+$ intermediate states, and then the $B^0_s$, $χ_{c0}$ and $D^0$ resonances decay into $K^+K^-$ components, which undergo final state interaction. The mode of the $B^+_c\rightarrow D^0(\rightarrow K^-π^+)K^+$ is also associated to the calculation, in this mode the intermediate resonance $D^0$ decays to the $K^-π^+$ final mesons. The resonances $B^0_s$, $χ_{c0}$ and $D^0$ effects in the $B^+_c\rightarrow B^0_s(\rightarrow K^+K^-)π^+$, $B^+_c\rightarrow χ_{c0}(\rightarrow K^+K^-)π^+$ and $B^+_c\rightarrow D^0(\rightarrow K^+K^-)π^+, D^0(\rightarrow K^-π^+)K^+$ decays are described in terms of the quasi-two-body modes. There is a weak annihilation nonresonant contribution in which $B^+_c$ decays to the $K^+K^-π^+$ directly, so the point-like 3-body matrix element $\langle K^+K^-π^+|u\bar{d}|0\rangle$ is also considered. The decay mode of the $B^+_c\rightarrow \bar{K}^{*0}(892)K^+$ is contributed to the annihilation contribution. The branching ratios of quasi-two-body decays expand in the range from $1.98\times10^{-6}$ to $7.32\times10^{-6}$.

hep-ph↗

arXiv2023

Estimating the branching fraction for $B^0\rightarrow ψ(2S)π^0$ decay

I present estimates of the branching fractions in the non-leptonic charmonium two-body decay rates for $B^0\rightarrow ψ(2S)π^0$ decay and the same decays of $B^+\rightarrow ψ(2S)π^+$, $B^0\rightarrow ψ(2S)K^0$ and $B^+\rightarrow ψ(2S)K^+$. These estimates are based on a generalized factorization approach making use of leading order (LO) and next-to-leading order (NLO) contributions. I find that when the large enhancements from the known NLO contributions by using the QCD factorization approach are taken into account, the branching ratios are the following: $Br(B^0\rightarrow ψ(2S)π^0)=(1.067\pm0.059)\times10^{-5}$, $Br(B^+\rightarrow ψ(2S)π^+)=(2.134\pm0.0.118)\times10^{-5}$, $Br(B^0\rightarrow ψ(2S)K^0)=(6.344\pm0.376)\times10^{-4}$ and $Br(B^+\rightarrow ψ(2S)K^+)=(6.344\pm0.376)\times10^{-4}$, while the experimental results are $(1.17\pm 0.17)\times 10^{-5}$, $(2.44\pm 0.30)\times 10^{-5}$, $(6.20\pm 0.50)\times 10^{-4}$ and $(6.39\pm 0.33)\times 10^{-4}$ respectively. All estimates are in good agreement with the experimental results.

hep-ph↗

arXiv2022

Calculation of branching fraction and $CP$ violation in $B^-\rightarrow D_s^-D^0$ decay

The most precise measurement of the $CP$ asymmetry in the decay $B^-\rightarrow D_s^-D^0$ has been reported by LHCb collaboration with the value of $(-0.4\pm0.5\pm0.5)\%$. In this study, the $CP$ violation in the decay $B^-\rightarrow D_s^-D^0$ has been calculated under the factorization approach. This decay mode includes current-current tree and penguin diagrams and their amplitudes are considered separately. In each of the tree and penguin amplitudes, the strong and weak phases have been introduced. The $CP$ asymmetry has been calculated in this work to be $(-0.35\pm0.03)\%$. Finally, from the sum of the amplitudes, we have calculated the total amplitude and obtained comparable results with experimental value for the branching ratio of $B^-\rightarrow D_s^-D^0$ decay.

hep-ph↗

arXiv2019

Evaluation of the $B^+_c\rightarrow D^0K^+$ decay by the factorization approaches and applying the effects of the final state interaction

In this paper the decay of $B^+_c$ meson, consisting of two b and c heavy quarks, into the $D^0$ and $K^+$ mesons is studied. Given that the experimental branching ratio for this decay is within the range of $3.72\times 10^{-5}$ to $11.16\times10^{-5}$ and in our estimating the theoretical result by using the QCD factorization approaches is $10^2$ times less than experimental one (we have obtained $1.41\times10^{-7}$), it is decided to calculate the theoretical branching ratio by applying the final state interaction (FSI) through the T and cross section channels. In this process, before the $B^+_c$ meson decays into two final state mesons of $D^0K^+$, it first decays into two intermediate mesons like $J/ψD^{*+}_s$, then these two mesons transformed into two final mesons by exchanging another meson like $D^0$. The FSI effects are very sensitive to the changes in the phenomenological parameter that appear in the form factor relation, as in most calculation changing two units in this parameter, makes the final result multiply in the branching ratio, therefor the decision to use FSI is not unexpected. In this study there are nineteen intermediate states in which the contribution of each one is calculated and summed in the final amplitude. Therefore, the numerical value of the branching ratio of $B^+_c\rightarrow D^0K^+$ decay is obtained by calculating the FSI effects from $1.17\times10^{-5}$ to $11.65\times10^{-5}$ which is consistent with the experimental result.

hep-ph↗